**Lignocellulosic Precursors Used in the Elaboration of Activated Carbon**

A. Alicia Peláez-Cid and M.M. Margarita Teutli-León *Benemérita Universidad Autónoma de Puebla México* 

#### **1. Introduction**

VIII Preface

• Chapter 4: Provides an overview of the application of activated carbons obtained from lignocellulosic precursors for wastewater treatment. Analysis and discussion are focused on the performance of different activated carbons obtained from several precursors and their advantages and capabilities for the

• Chapter 5: Analyses the use of pyrolysis for the valorization of two Mexican typical agricultural wastes (orange peel and pecan nut shell) for energy and carbon production. Also, the analysis of pyrolysis yields for various biomasses at different conditions is reported and, finally the composition of the liquid fractions (i.e., bio-oil) obtained from the pyrolysis of orange peel and pecan

I would like to thank all the authors for their excellent contributions to this book and to Instituto Tecnológico de Aguascalientes for the facilities to work in this project.

> **Ph.D Virginia Hernández Montoya** Instituto Tecnológico de Aguascalientes

> > México

removal of relevant toxic compounds and pollutants from water.

nut shell were analysed.

Many authors have defined activated carbon taking into account its most outstanding properties and characteristics. In this chapter, activated carbon will be defined stating that it is an excellent adsorbent which is produced in such a way that it exhibits high specific surface area and porosity. These characteristics, along with the surface's chemical nature (which depends on the raw materials and the activation used in its preparation process), allow it to attract and retain certain compounds in a preferential way, either in liquid or gaseous phase. Activated carbon is one of the most commonly used adsorbents in the removal process of industrial pollutants, organic compounds, heavy metals, herbicides, and dyes, among many others toxic and hazardous compounds.

The world's activated carbon production and consumption in the year 2000 was estimated to be 4 x 108 kg (Marsh, 2001). By 2005, it had doubled (Elizalde-González, 2006) with a production yield of 40%. In the industry, activated carbon is prepared by means of oxidative pyrolysis starting off soft and hardwoods, peat, lignite, mineral carbon, bones, coconut shell, and wastes of vegetable origin (Girgis et al., 2002; Marsh, 2001).

There are two types of carbon activation procedures: Physical (also known as thermal) and chemical. During physical activation, the lignocellulosic material as such or the previously carbonized materials can undergo gasification with water vapor, carbon dioxide, or the same combustion gases produced during the carbonization. Ammonium persulfate, nitric acid, and hydrogen peroxide have also been used as oxidizing agents (Salame & Bandoz, 2001). Chemical activation consists of impregnating the lignocellulosic or carbonaceous raw materials with chemicals such as ZnCl2, H3PO4, HNO3, H2SO4, NaOH, or KOH (Elizalde-González & Hernández-Montoya, 2007; Girgis et al., 2002). Then, they are carbonized (a process now called "pyrolysis") and, finally, washed to eliminate the activating agent. The application of a gaseous stream such as air, nitrogen, or argon is a common practice during pyrolysis which generates a better development of the material's porosity. Although not commonly, compounds such as potassium carbonate, a cleaner chemical agent (Tsai et al., 2001b; 2001c) or formamide (Cossarutto et al., 2001) have been also used as activating agents.

**2. Characteristics of the selected raw materials for activated carbon production**  The materials selected nowadays to be potential precursors of activated carbons must fulfill

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 3

1) They must be materials with high carbon contents and low inorganic compound levels (Tsai et al., 1998) in order to obtain a better yield during the carbonization processes. This is valid for practically every lignocellulosic wastes. They must be plentiful in the region or country where they will be used to solve any specific environmental issue. For example, corncob has been used to produce activated carbon and, according to Tsai et al. (1997), corn grain is a very important agricultural product in Taiwan. The same condition applies for the avocado, mango, orange, and guava seeds in Mexico (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2007, 2008, 2009a, 2009b, 2009c; Dávila-Jiménez et al., 2009). Specifically, Mexico has ranked number one in the world for avocado production, number two for mango, and number four for orange (Salunkhe & Kadam, 1995). On the other hand, jute stick is abundantly available in Bangladesh and India (Asadullah et al., 2007), from which bio-oil is obtained, and the process's residue has been used to produce activated carbon. Bamboo, an abundant and inexpensive natural resource in Malaysia, was also used to prepare activated carbon (Hameed et al., 2007). Cherry pits are an industrial byproduct abundantly generated in the Jerte valley at Spain's Caceres province (Olivares-Marín et al., 2006). Other important wastes generated in Spain that have also been proposed with satisfying results in the production of activated carbon with high porosity and specific surface area are: olive-mill waste generated in large amounts during the manufacture of olive oil (Moreno-Castilla et al., 2001) and olive-tree wood generated during the trimming process of olive trees done to make their development adequate (Ould-Idriss et al., 2011).

2) The residue generated during consumption or industrial use of lignocellulosic materials regularly represents a high percentage of the source from which it is obtained. For example, mango seed is around 15 to 20 % of manila mango from which it is obtained (Salunkhe & Kadam, 1995). In the case of avocado, 10 to 13 % of the fruit weight corresponds to the kernel seed and it is garbage after consumption (Elizalde-González et al., 2007). Corn cob is approximately 18 % of corn grain (Tsai et al., 2001b). Orange seeds constitute only about 0.3 % of the fresh mature fruit (Elizalde-González & Hernández-Montoya, 2009c), but orange is the most produced and most consumed fruit worldwide (Salunkhe & Kadam, 1995). Sawdust does not constitute a net percentage of tree residue, rather, it is a waste obtained from wood applications conditioning. However, it has proven to be a good precursor when

3) They must be an effective and economic material to be used as an adsorbent for the removal of pollutants from both gaseous and liquid systems. Specifically, carbons produced from lignocellulosic precursors have been used to eliminate basic dyes (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2007; Girgis et al., 2002; Hameed et al., 2007; Rajeshwarisivaraj et al., 2001), acid dyes (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2008, 2009a, 2009b, 2009c; Malik, 2003; Rajeshwarisivaraj et al., 2001; Tsai et al., 2001a), reactive dyes (Elizalde-González et al., 2007; Senthilkumaara et al., 2006), direct dyes (Kamal, 2009; Namasivayam & Kavitha, 2002; Rajeshwarisivaraj et al., 2001), metallic ions such as Cr4+, Hg2+ and Fe2+ (Rajeshwarisivaraj et al., 2001), Eu3+

the following demands:

it is obtained from mahogany (Malik, 2003).

Commercial activated carbon is produced as powder (PAC), fibers (FAC), or granules (GAC) depending on its application. It regularly exhibits BET specific surface magnitudes between 500 and 2000 m2g-1. However, the so-called "super-activated carbons" exhibit surfaces areas above 3000 m2g-1. Activated carbon's macro, meso, and micropore volumes may range from 0.5 to 2.5 cm3g-1 (Marsh, 2001).

The adsorption capabilities of activated carbon are very high because of its high specific surface, originated by porosity. Also, depending on what type of activation was used, the carbon's surface may exhibit numerous functional groups, which favor the specific interactions that allow it to act as an ionic interchanger with the different kinds of pollutants. an

The activated carbon is commonly considered an expensive material because of the chemical and physical treatments used in its synthesis, its low yield, its production's high energy consumption, or the thermal treatments used for its regeneration and the losses generated meanwhile. However, if its high removal capacity compared to other adsorbents is considered, the cost of production does not turn out to be very high. The search for the appropriate mechanism for its pyrolysis process is an important factor for tackling production costs.

The exhausted material's thermal regeneration (Robinson et al., 2001) consists of drying the wet carbon, pyrolysis of the adsorbed organic compounds, and reactivating the carbon, which generates mass losses up to 15 %. The carbon's regeneration can also be accomplished by using water vapor or solvents to desorb the absorbed substances, which, in turn, leads to a new problem regarding pollution. Because of these environmental inconveniences as well as the loss in adsorption capacity and the increase in costs which the regeneration process implies, using new carbon once the old one's surface has been saturated is often preferred.

With the goal of diminishing the cost of producing activated carbon, contemporary research is taking a turn towards industrial or vegetable (lignocellulosic) wastes to be used as raw material, and, then, lessen the cost of production (Konstantinou & Pashalidis, 2010). Besides, the use of these precursors reduces residue generation in both rural and urban areas.

This chapter presents a twenty-year (1992 – 2011) worldwide research review regarding a large amount of lignocellulosic materials proposed as potential precursors in the production of activated carbon. The most common characteristics that lignocellulosic wastes used in carbon production and the parameters that control porosity development and, hence, the increase in specific surface during carbonization are also mentioned. A comparison between countries whose scientists are interested in carbon preparation from alternative waste lignocellulosic materials by continent is made. The most commonly used agents for chemical, physical, or a combination of both activations methods which precursors undergo are shown.

2 Characterization Techniques and Applications in the Wastewater Treatment

Commercial activated carbon is produced as powder (PAC), fibers (FAC), or granules (GAC) depending on its application. It regularly exhibits BET specific surface magnitudes between 500 and 2000 m2g-1. However, the so-called "super-activated carbons" exhibit surfaces areas above 3000 m2g-1. Activated carbon's macro, meso, and micropore volumes

The adsorption capabilities of activated carbon are very high because of its high specific surface, originated by porosity. Also, depending on what type of activation was used, the carbon's surface may exhibit numerous functional groups, which favor the specific interactions that allow it to act as an ionic interchanger with the different kinds of

The activated carbon is commonly considered an expensive material because of the chemical and physical treatments used in its synthesis, its low yield, its production's high energy consumption, or the thermal treatments used for its regeneration and the losses generated meanwhile. However, if its high removal capacity compared to other adsorbents is considered, the cost of production does not turn out to be very high. The search for the appropriate mechanism for its pyrolysis process is an important factor for tackling

The exhausted material's thermal regeneration (Robinson et al., 2001) consists of drying the wet carbon, pyrolysis of the adsorbed organic compounds, and reactivating the carbon, which generates mass losses up to 15 %. The carbon's regeneration can also be accomplished by using water vapor or solvents to desorb the absorbed substances, which, in turn, leads to a new problem regarding pollution. Because of these environmental inconveniences as well as the loss in adsorption capacity and the increase in costs which the regeneration process implies, using new carbon once the old one's surface has been saturated is often preferred.

With the goal of diminishing the cost of producing activated carbon, contemporary research is taking a turn towards industrial or vegetable (lignocellulosic) wastes to be used as raw material, and, then, lessen the cost of production (Konstantinou & Pashalidis, 2010). Besides,

This chapter presents a twenty-year (1992 – 2011) worldwide research review regarding a large amount of lignocellulosic materials proposed as potential precursors in the production of activated carbon. The most common characteristics that lignocellulosic wastes used in carbon production and the parameters that control porosity development and, hence, the increase in specific surface during carbonization are also mentioned. A comparison between countries whose scientists are interested in carbon preparation from alternative waste lignocellulosic materials by continent is made. The most commonly used agents for chemical, physical, or a combination of both activations methods which precursors undergo

the use of these precursors reduces residue generation in both rural and urban areas.

may range from 0.5 to 2.5 cm3g-1 (Marsh, 2001).

pollutants.

production costs.

are shown.

#### **2. Characteristics of the selected raw materials for activated carbon production**

The materials selected nowadays to be potential precursors of activated carbons must fulfill the following demands:

1) They must be materials with high carbon contents and low inorganic compound levels (Tsai et al., 1998) in order to obtain a better yield during the carbonization processes. This is valid for practically every lignocellulosic wastes. They must be plentiful in the region or country where they will be used to solve any specific environmental issue. For example, corncob has been used to produce activated carbon and, according to Tsai et al. (1997), corn grain is a very important agricultural product in Taiwan. The same condition applies for the avocado, mango, orange, and guava seeds in Mexico (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2007, 2008, 2009a, 2009b, 2009c; Dávila-Jiménez et al., 2009). Specifically, Mexico has ranked number one in the world for avocado production, number two for mango, and number four for orange (Salunkhe & Kadam, 1995). On the other hand, jute stick is abundantly available in Bangladesh and India (Asadullah et al., 2007), from which bio-oil is obtained, and the process's residue has been used to produce activated carbon. Bamboo, an abundant and inexpensive natural resource in Malaysia, was also used to prepare activated carbon (Hameed et al., 2007). Cherry pits are an industrial byproduct abundantly generated in the Jerte valley at Spain's Caceres province (Olivares-Marín et al., 2006). Other important wastes generated in Spain that have also been proposed with satisfying results in the production of activated carbon with high porosity and specific surface area are: olive-mill waste generated in large amounts during the manufacture of olive oil (Moreno-Castilla et al., 2001) and olive-tree wood generated during the trimming process of olive trees done to make their development adequate (Ould-Idriss et al., 2011).

2) The residue generated during consumption or industrial use of lignocellulosic materials regularly represents a high percentage of the source from which it is obtained. For example, mango seed is around 15 to 20 % of manila mango from which it is obtained (Salunkhe & Kadam, 1995). In the case of avocado, 10 to 13 % of the fruit weight corresponds to the kernel seed and it is garbage after consumption (Elizalde-González et al., 2007). Corn cob is approximately 18 % of corn grain (Tsai et al., 2001b). Orange seeds constitute only about 0.3 % of the fresh mature fruit (Elizalde-González & Hernández-Montoya, 2009c), but orange is the most produced and most consumed fruit worldwide (Salunkhe & Kadam, 1995). Sawdust does not constitute a net percentage of tree residue, rather, it is a waste obtained from wood applications conditioning. However, it has proven to be a good precursor when it is obtained from mahogany (Malik, 2003).

3) They must be an effective and economic material to be used as an adsorbent for the removal of pollutants from both gaseous and liquid systems. Specifically, carbons produced from lignocellulosic precursors have been used to eliminate basic dyes (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2007; Girgis et al., 2002; Hameed et al., 2007; Rajeshwarisivaraj et al., 2001), acid dyes (Elizalde-González et al., 2007; Elizalde-González & Hernández-Montoya, 2008, 2009a, 2009b, 2009c; Malik, 2003; Rajeshwarisivaraj et al., 2001; Tsai et al., 2001a), reactive dyes (Elizalde-González et al., 2007; Senthilkumaara et al., 2006), direct dyes (Kamal, 2009; Namasivayam & Kavitha, 2002; Rajeshwarisivaraj et al., 2001), metallic ions such as Cr4+, Hg2+ and Fe2+ (Rajeshwarisivaraj et al., 2001), Eu3+

**3.4 Carbonizing temperature** 

Quinn, 1996).

**3.5 Carbonizing time** 

**3.6 Gas flow speed** 

**3.7 Effect of washing process** 

**4. Worldwide studied precursors** 

It has the most influence over the activated carbon's quality during the activating process. It must be at least 400 °C to ensure the complete transformation of organic compounds (present in lignocellulosic precursors) into graphene structures. The degree of specific surface area development and porosity is incremented on par with the carbonizing temperature (Olivares-Marín et al., 2006b). During physical activation, carbonization temperatures are greater than those needed for chemical activation (Lussier et al., 1994). However, carbonization temperatures used in activated carbon production are generally greater than 400 °C and temperatures ranging from 120 to 1000 °C have been used. (Elizalde et al., 2007; Elizalde-González & Hernández-Montoya, 2008; Rajeshwarisivaraj et al., 2001; Salame & Bandosz, 2001). It has been reported that carbon obtained from peach pits with temperatures below 700 °C still have a high content of hydrogen and oxygen (MacDonald &

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 5

This parameter must be optimized to obtain the maximum porosity development while still minimizing the material's loss due to an excessive combustion. Bouchelta et al. (2008) have shown that the yield percentage decreases with increase of activation temperature and hold time. Carbonization times ranging from 1 h (Rajeshwarisivaraj et al., 2001; Wu et al., 1999)

It has been observed that during pyrolysis, the passing on an inert gas, such as N2 or Ar, favors the development in the carbon's porosity. In this case, the flow and the gas type may affect the final properties of the activated carbon. CO2 flow-rate had a significant influence

During the lignocellulosic residue's pyrolysis, the presence of chemical activating agents generates carbons with a more orderly structure. The later elimination of chemical activating agents, by means of successive washings, will allow a better development of porosity.

Numerous lignocellulosic residues have been selected as potential activated carbon precursors. Among them, there is the wood obtained from several kinds of tree species such as *Eucalyptus* (Bello et al., 2002; Ngernyen et al., 2006; Rodrígez-Mirasol et al., 1993), pine (Giraldo & Moreno-Piraján, 2007; Sun et al., 2008), *Quercus agrifolia* (Robau-Sánchez et al., 2001), wattle (Ngernyen et al., 2006), china fir (Zuo et al., 2010), acacia (Kumar et al., 1992), olive tree (Ould-Idriss et al., 2011), softwood bark (Cao et al., 2002), mahogany sawdust (Malik, 2003), sawdust flash ash (Aworn et al., 2008), and sawdust (Giraldo & Moreno-Piraján, 2008; Zhang et al., 2010), coconut shell (Cossarutto et al., 2001; Giraldo & Moreno-Piraján, 2007; Hayashi et al., 2002; Heschel & Klose, 1995; Hu et al., 2001; Kannan & Sundaram, 2001), coconut fiber (Namasivayam & Kavitha, 2002; Phan et al., 2006; Senthilkumaara et al., 2006), corn cob (Aworn et al., 2008; Tsai et al., 1997; 1998; 2001a;

up to 14 h (Rajeshwarisivaraj et al., 2001) have been used in charcoal production.

on the development of the surface area of oil palm stones (Lua & Guo, 2000).

(Konstantinou & Pashalidis, 2010), Cu2+ (Dastgheib & Rockstraw, 2001; Konstantinou & Pashalidis, 2010; Toles et al., 1997) or Pb2+ (Giraldo & Moreno-Piraján, 2008), and low molecular mass organic compounds such as phenol (Giraldo & Moreno-Piraján, 2007; Wu et al., 1999, 2001), chlorophenol (Wu et al., 2001), and nitro phenol (Giraldo & Moreno-Piraján, 2008). For example, bamboo powder charcoal has demonstrated being an attractive option for treatment of superficial and subterranean water polluted by nitrate-nitrogen (Mizuta et al., 2004). Carbon produced from bamboo waste (Ahmad & Hammed, 2010) as well as the one obtained from avocado peel (Singh & Kumar, 2008) have proven effective in diminishing COD during the treatment of cotton textile mill wastewater and wastewater from coffee processing plant, respectively. Carbon molecular sieves for separating gaseous mixtures are another application of activated carbons prepared from lignocellulosic precursors (Ahmad et al., 2007; Bello et al., 2002).

#### **3. Parameters for activated carbon preparation**

Research has shown that carbons's properties such as specific surface area, porosity, density and mechanical resistance depend greatly on the raw material used. However, it may be possible to modify these parameters changing the conditions in the pyrolysis process of the lignocellulosic materials.

In particular, the most important parameters to be considered while preparing activated carbons from lignocellulosic materials are described below.

#### **3.1 Activating agent**

H3PO4 is the most commonly used chemical agent for synthesis of activated carbon. The use of ZnCl2 has declined because of the environmental pollution problems with zinc disposal (Girgis et al., 2002). In the case of physical activation, the use of water vapor and carbon dioxide is preferred to promote the partial oxidation of the surface instead of oxygen, which is too reactive.

#### **3.2 Mass ratio of precursor and activating agent**

The complete saturation of lignocellulosic precursor must be ensured to develop the adsorbent porosity with the minimum activating agent consumption. This leads a minor consumption of chemical compounds and a better elimination of the excess during the carbon washing process. The effect of the increase in proportion of the impregnation over the carbon porous structure is greater than the one obtained with the increase of carbonizing temperature (Olivares-Marín et al., 2006a).

#### **3.3 Heating speed**

Regularly, heating ramps with a low speed are used for preparation of activated carbon. This approach allows the complete combustion of material precursor and favors a better porosity development. Rapid heating during pyrolysis produces macroporous residue (Heschel & Klose, 1995).

#### **3.4 Carbonizing temperature**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

4 Characterization Techniques and Applications in the Wastewater Treatment

(Konstantinou & Pashalidis, 2010), Cu2+ (Dastgheib & Rockstraw, 2001; Konstantinou & Pashalidis, 2010; Toles et al., 1997) or Pb2+ (Giraldo & Moreno-Piraján, 2008), and low molecular mass organic compounds such as phenol (Giraldo & Moreno-Piraján, 2007; Wu et al., 1999, 2001), chlorophenol (Wu et al., 2001), and nitro phenol (Giraldo & Moreno-Piraján, 2008). For example, bamboo powder charcoal has demonstrated being an attractive option for treatment of superficial and subterranean water polluted by nitrate-nitrogen (Mizuta et al., 2004). Carbon produced from bamboo waste (Ahmad & Hammed, 2010) as well as the one obtained from avocado peel (Singh & Kumar, 2008) have proven effective in diminishing COD during the treatment of cotton textile mill wastewater and wastewater from coffee processing plant, respectively. Carbon molecular sieves for separating gaseous mixtures are another application of activated carbons prepared from lignocellulosic

Research has shown that carbons's properties such as specific surface area, porosity, density and mechanical resistance depend greatly on the raw material used. However, it may be possible to modify these parameters changing the conditions in the pyrolysis process of the

In particular, the most important parameters to be considered while preparing activated

H3PO4 is the most commonly used chemical agent for synthesis of activated carbon. The use of ZnCl2 has declined because of the environmental pollution problems with zinc disposal (Girgis et al., 2002). In the case of physical activation, the use of water vapor and carbon dioxide is preferred to promote the partial oxidation of the surface instead of oxygen, which

The complete saturation of lignocellulosic precursor must be ensured to develop the adsorbent porosity with the minimum activating agent consumption. This leads a minor consumption of chemical compounds and a better elimination of the excess during the carbon washing process. The effect of the increase in proportion of the impregnation over the carbon porous structure is greater than the one obtained with the increase of carbonizing

Regularly, heating ramps with a low speed are used for preparation of activated carbon. This approach allows the complete combustion of material precursor and favors a better porosity development. Rapid heating during pyrolysis produces macroporous residue

precursors (Ahmad et al., 2007; Bello et al., 2002).

lignocellulosic materials.

**3.1 Activating agent** 

is too reactive.

**3.3 Heating speed** 

(Heschel & Klose, 1995).

**3. Parameters for activated carbon preparation** 

carbons from lignocellulosic materials are described below.

**3.2 Mass ratio of precursor and activating agent** 

temperature (Olivares-Marín et al., 2006a).

It has the most influence over the activated carbon's quality during the activating process. It must be at least 400 °C to ensure the complete transformation of organic compounds (present in lignocellulosic precursors) into graphene structures. The degree of specific surface area development and porosity is incremented on par with the carbonizing temperature (Olivares-Marín et al., 2006b). During physical activation, carbonization temperatures are greater than those needed for chemical activation (Lussier et al., 1994). However, carbonization temperatures used in activated carbon production are generally greater than 400 °C and temperatures ranging from 120 to 1000 °C have been used. (Elizalde et al., 2007; Elizalde-González & Hernández-Montoya, 2008; Rajeshwarisivaraj et al., 2001; Salame & Bandosz, 2001). It has been reported that carbon obtained from peach pits with temperatures below 700 °C still have a high content of hydrogen and oxygen (MacDonald & Quinn, 1996).

#### **3.5 Carbonizing time**

This parameter must be optimized to obtain the maximum porosity development while still minimizing the material's loss due to an excessive combustion. Bouchelta et al. (2008) have shown that the yield percentage decreases with increase of activation temperature and hold time. Carbonization times ranging from 1 h (Rajeshwarisivaraj et al., 2001; Wu et al., 1999) up to 14 h (Rajeshwarisivaraj et al., 2001) have been used in charcoal production.

#### **3.6 Gas flow speed**

It has been observed that during pyrolysis, the passing on an inert gas, such as N2 or Ar, favors the development in the carbon's porosity. In this case, the flow and the gas type may affect the final properties of the activated carbon. CO2 flow-rate had a significant influence on the development of the surface area of oil palm stones (Lua & Guo, 2000).

#### **3.7 Effect of washing process**

During the lignocellulosic residue's pyrolysis, the presence of chemical activating agents generates carbons with a more orderly structure. The later elimination of chemical activating agents, by means of successive washings, will allow a better development of porosity.

#### **4. Worldwide studied precursors**

Numerous lignocellulosic residues have been selected as potential activated carbon precursors. Among them, there is the wood obtained from several kinds of tree species such as *Eucalyptus* (Bello et al., 2002; Ngernyen et al., 2006; Rodrígez-Mirasol et al., 1993), pine (Giraldo & Moreno-Piraján, 2007; Sun et al., 2008), *Quercus agrifolia* (Robau-Sánchez et al., 2001), wattle (Ngernyen et al., 2006), china fir (Zuo et al., 2010), acacia (Kumar et al., 1992), olive tree (Ould-Idriss et al., 2011), softwood bark (Cao et al., 2002), mahogany sawdust (Malik, 2003), sawdust flash ash (Aworn et al., 2008), and sawdust (Giraldo & Moreno-Piraján, 2008; Zhang et al., 2010), coconut shell (Cossarutto et al., 2001; Giraldo & Moreno-Piraján, 2007; Hayashi et al., 2002; Heschel & Klose, 1995; Hu et al., 2001; Kannan & Sundaram, 2001), coconut fiber (Namasivayam & Kavitha, 2002; Phan et al., 2006; Senthilkumaara et al., 2006), corn cob (Aworn et al., 2008; Tsai et al., 1997; 1998; 2001a;

are called coal. Both kinds are susceptible to chemical, physical, or a combination of both

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 7

It has been found that the activated carbon's properties depend greatly on the composition of their raw materials (Gergova et al., 1993; Girgis et al., 2002). Development of porosity and active sites with a specific character is aided by physical activation because a partial oxidation occurs, and the carbon's surface is enriched with several functional groups (Salame & Bandoz, 2001). Chemical activation further develops these characteristics. Additionally, chemical activation has several advantages over physical activation. Besides, it is done at lower temperatures. Some authors have chosen a combination of both methods to produce their activated carbons for fitting specific applications. For example, it can be cited the activated carbon obtained from coconut peel activated with water vapor and then treated with formamide to accomplish the adsorption of the vapor (Cossarutto et al., 2001). On the other hand, there are wood carbons chemically activated with H3PO4 and KOH, and then treated with ammonia persulfate, nitric acid, or hydrogen peroxide (as oxidating agents) with the objective of obtaining carbons either with the nitro- group with positive charges on the nitrogen atom or with negative charges on the oxygen atoms, making them

Pecan

Wattle Cedar Stem of date China fir Hazelnut Seeds Acacia Pistachio Stones Olive tree Walnut Coconut Shell

Pine Almond Pit *Quercus agrifolia* Macadamia Shell

Mahogany sawdust Apricot Straw Rice Sawdust flash ash Peach Wheat

Peach Date Cassava Plum Olive Pomegranate

Grape Coffee bean Stick Orange Mango Coffee Ground Guava *Moringa Oleifera* Residue Mango Corncob Peanut hull Rapeseed Cork waste *Macuna musitana* Kenaf Cotton stalks Flamboyant pods

Table 1. Waste materials used in activated carbon production grouped according to their source.

Although some carbons obtained from corn cob with a BET specific surface up to 2595 m2g-1 have been prepared via chemical activation with KOH (Tseng & Tseng, 2005), high surface areas can be obtained by means of physical activation. These carbons reach values of 1400 m2g-1 or more using *Eucaliptus* as the precursor and CO2 as an oxydating agent (Ngernyen et

Sugarcane bagasse Vine shoot Olive cake Bamboo powder

Palm

Cherry Fiber

Peel

Rice Jute Fibers

Fiber

Avocado

activation types to produce the outstanding activated carbons.

better adsorbents for ionic species (Salame & Bandoz, 2001).

Nuts Shells

Stones

Husks

Sawdust Plum

Wood

Seeds

*Eucalyptus*

Softwood bark

Avocado

2001b; Tseng & Tseng, 2005; Wu et al., 2001), cherry stones (Gergova et al., 1993; 1994; Heschel & Klose, 1995; Lussier et al., 1994; Olivares-Marín et al., 2006a; 2006b), apricot stones (Gergova et al., 1993; 1994), peach stones (Heschel & Klose, 1995; MacDonald & Quinn, 1996; Molina-Sabio et al., 1995; 1996; Rodríguez-Reinoso & Molina-Sabio, 1992) and peach seed (Giraldo & Moreno-Piraján, 2007), mixture of apricot and peach stones (Puziy et al., 2005), wheat straw (Kannan & Sundaram, 2001), rice straw (Ahmedna et al., 2000) and rice husks (Ahmedna et al., 2000; Aworn et al., 2008; Kalderis et al., 2008; Kannan & Sundaram, 2001; Malik, 2003; Swarnalatha et al., 2009), sugarcane bagasse (Ahmedna et al., 2000; Aworn et al., 2008; Giraldo & Moreno-Piraján, 2007; Juang et al., 2002; 2008; Kalderis et al., 2008; Tsai et al., 2001;), palm fiber (Guo et al., 2008), palm pit (Giraldo & Moreno-Piraján, 2007; 2008), palm shell (Ahmad et al., 2007; Arami-Niya et al., 2010; Hayashi et al., 2002), stem of date palm (Jibril et al., 2008), and palm seeds (Gou et al., 2008; Hu et al., 2001), palm stones (Lua & Guo, 2000), pecan shells (Ahmedna et al., 2000; Dastgheib & Rockstraw, 2001; Toles et al., 1997), almond shells (Gergova et al., 1994; Hayashi et al., 2002; Iniesta et al., 2001; Mourao et al., 2011; Nabais et al., 2011; Rodríguez-Reinoso & Molina-Sabio, 1992; Toles et al., 1997), macadamia shells (Aworn et al., 2008; Evans et al., 1999), cedar nut shells (Baklanova et al., 2003), hazelnut shells (Heschel & Klose, 1995), pistachio shell (Hayashi et al., 2002), and walnut shells (Hayashi et al., 2002; Heschel & Klose, 1995), bamboo powder (Ahmad & Hameed, 2010; Hammed et al., 2007; Kannan & Sundaram, 2001; Mizuta et al., 2004), jute fibers (Asadullah et al., 2007; Phan et al., 2006; Senthilkumaara et al., 2006), plum kernels (Heschel & Klose, 1995; Wu et al., 1999), avocado kernel seeds (Elizalde-González et al., 2007) and avocado peel (Devi et al., 2008), coffee bean husks (Baquero et al., 2003), coffee residue (Boudrahem et al., 2009), and coffee ground (Evans et al., 1999), date stones (Bouchelta et al., 2008; Hazourli et al., 2009), grape seeds (Gergova et al., 1993, 1994), vine shoot (Mourao et al., 2011), orange seeds (Elizalde-González & Hernández-Montoya, 2008, 2009c) and guava seeds (Elizalde-González & Hernández-Montoya, 2008, 2009a, 2009b), mango pit (husk and seed) (Dávila-Jimenez et al., 2009; Elizalde-González & Hernández-Montoya, 2007; 2008), olive stones (Rodríguez-Reinoso & Molina-Sabio, 1992; Yavuz et al., 2010) and olive cake (Konstantinou & Pashalidis, 2010; Moreno-Castilla et al., 2001), peanut hull (Girgis et al., 2002; Kannan & Sundaram, 2001), cassava peel (Rajeshwarisivaraj et al., 2001), pomegranate peel (Amin, 2009), cotton stalks (Girgis & Ishak, 1999), kenaf (Valente-Nabais et al., 2009), cork waste (Carvalho et al., 2004), flamboyant pods (A.M.M. Vargas et al., 2011), rapeseed (Valente-Nabais et al., 2009), *Macuna musitana* (Vargas et al., 2010), and seed husks of *Moringa Oleifera* (Warhurst et al., 1997). Table 1 shows clearly the lignocellulosic precursors used in activated carbon production classified according to the source they were obtained from.

Figure 1 shows the great variety of lignocellulosic residues used in worldwide production of activated carbon. It can be observed that wood from several tree species, several kinds of nuts, or different coconut parts are among the most commonly used along with the traditional raw materials used for the preparation of activated carbon. This figure shows that from a single vegetable, different parts have been tested as precursors. For example, the seed and peel of avocado have been studied (Elizalde et al., 2007; Singh & Kumar, 2008). The same condition applies for the rice straw (Ahmedna et al., 2000) and the rice husk (Kalderis et al., 2008; Swarnalatha et al., 2009). Note that when carbons are prepared with lignocellulosic precursors, they are called charcoal. If they are of mineral origin, then they

6 Characterization Techniques and Applications in the Wastewater Treatment

2001b; Tseng & Tseng, 2005; Wu et al., 2001), cherry stones (Gergova et al., 1993; 1994; Heschel & Klose, 1995; Lussier et al., 1994; Olivares-Marín et al., 2006a; 2006b), apricot stones (Gergova et al., 1993; 1994), peach stones (Heschel & Klose, 1995; MacDonald & Quinn, 1996; Molina-Sabio et al., 1995; 1996; Rodríguez-Reinoso & Molina-Sabio, 1992) and peach seed (Giraldo & Moreno-Piraján, 2007), mixture of apricot and peach stones (Puziy et al., 2005), wheat straw (Kannan & Sundaram, 2001), rice straw (Ahmedna et al., 2000) and rice husks (Ahmedna et al., 2000; Aworn et al., 2008; Kalderis et al., 2008; Kannan & Sundaram, 2001; Malik, 2003; Swarnalatha et al., 2009), sugarcane bagasse (Ahmedna et al., 2000; Aworn et al., 2008; Giraldo & Moreno-Piraján, 2007; Juang et al., 2002; 2008; Kalderis et al., 2008; Tsai et al., 2001;), palm fiber (Guo et al., 2008), palm pit (Giraldo & Moreno-Piraján, 2007; 2008), palm shell (Ahmad et al., 2007; Arami-Niya et al., 2010; Hayashi et al., 2002), stem of date palm (Jibril et al., 2008), and palm seeds (Gou et al., 2008; Hu et al., 2001), palm stones (Lua & Guo, 2000), pecan shells (Ahmedna et al., 2000; Dastgheib & Rockstraw, 2001; Toles et al., 1997), almond shells (Gergova et al., 1994; Hayashi et al., 2002; Iniesta et al., 2001; Mourao et al., 2011; Nabais et al., 2011; Rodríguez-Reinoso & Molina-Sabio, 1992; Toles et al., 1997), macadamia shells (Aworn et al., 2008; Evans et al., 1999), cedar nut shells (Baklanova et al., 2003), hazelnut shells (Heschel & Klose, 1995), pistachio shell (Hayashi et al., 2002), and walnut shells (Hayashi et al., 2002; Heschel & Klose, 1995), bamboo powder (Ahmad & Hameed, 2010; Hammed et al., 2007; Kannan & Sundaram, 2001; Mizuta et al., 2004), jute fibers (Asadullah et al., 2007; Phan et al., 2006; Senthilkumaara et al., 2006), plum kernels (Heschel & Klose, 1995; Wu et al., 1999), avocado kernel seeds (Elizalde-González et al., 2007) and avocado peel (Devi et al., 2008), coffee bean husks (Baquero et al., 2003), coffee residue (Boudrahem et al., 2009), and coffee ground (Evans et al., 1999), date stones (Bouchelta et al., 2008; Hazourli et al., 2009), grape seeds (Gergova et al., 1993, 1994), vine shoot (Mourao et al., 2011), orange seeds (Elizalde-González & Hernández-Montoya, 2008, 2009c) and guava seeds (Elizalde-González & Hernández-Montoya, 2008, 2009a, 2009b), mango pit (husk and seed) (Dávila-Jimenez et al., 2009; Elizalde-González & Hernández-Montoya, 2007; 2008), olive stones (Rodríguez-Reinoso & Molina-Sabio, 1992; Yavuz et al., 2010) and olive cake (Konstantinou & Pashalidis, 2010; Moreno-Castilla et al., 2001), peanut hull (Girgis et al., 2002; Kannan & Sundaram, 2001), cassava peel (Rajeshwarisivaraj et al., 2001), pomegranate peel (Amin, 2009), cotton stalks (Girgis & Ishak, 1999), kenaf (Valente-Nabais et al., 2009), cork waste (Carvalho et al., 2004), flamboyant pods (A.M.M. Vargas et al., 2011), rapeseed (Valente-Nabais et al., 2009), *Macuna musitana* (Vargas et al., 2010), and seed husks of *Moringa Oleifera* (Warhurst et al., 1997). Table 1 shows clearly the lignocellulosic precursors used in activated carbon production classified according to the

Figure 1 shows the great variety of lignocellulosic residues used in worldwide production of activated carbon. It can be observed that wood from several tree species, several kinds of nuts, or different coconut parts are among the most commonly used along with the traditional raw materials used for the preparation of activated carbon. This figure shows that from a single vegetable, different parts have been tested as precursors. For example, the seed and peel of avocado have been studied (Elizalde et al., 2007; Singh & Kumar, 2008). The same condition applies for the rice straw (Ahmedna et al., 2000) and the rice husk (Kalderis et al., 2008; Swarnalatha et al., 2009). Note that when carbons are prepared with lignocellulosic precursors, they are called charcoal. If they are of mineral origin, then they

source they were obtained from.

are called coal. Both kinds are susceptible to chemical, physical, or a combination of both activation types to produce the outstanding activated carbons.

It has been found that the activated carbon's properties depend greatly on the composition of their raw materials (Gergova et al., 1993; Girgis et al., 2002). Development of porosity and active sites with a specific character is aided by physical activation because a partial oxidation occurs, and the carbon's surface is enriched with several functional groups (Salame & Bandoz, 2001). Chemical activation further develops these characteristics. Additionally, chemical activation has several advantages over physical activation. Besides, it is done at lower temperatures. Some authors have chosen a combination of both methods to produce their activated carbons for fitting specific applications. For example, it can be cited the activated carbon obtained from coconut peel activated with water vapor and then treated with formamide to accomplish the adsorption of the vapor (Cossarutto et al., 2001). On the other hand, there are wood carbons chemically activated with H3PO4 and KOH, and then treated with ammonia persulfate, nitric acid, or hydrogen peroxide (as oxidating agents) with the objective of obtaining carbons either with the nitro- group with positive charges on the nitrogen atom or with negative charges on the oxygen atoms, making them better adsorbents for ionic species (Salame & Bandoz, 2001).


Table 1. Waste materials used in activated carbon production grouped according to their source.

Although some carbons obtained from corn cob with a BET specific surface up to 2595 m2g-1 have been prepared via chemical activation with KOH (Tseng & Tseng, 2005), high surface areas can be obtained by means of physical activation. These carbons reach values of 1400 m2g-1 or more using *Eucaliptus* as the precursor and CO2 as an oxydating agent (Ngernyen et al., 2006; Rodríguez-Mirasol et al., 1993). Figure 2 shows that the worldwide tendency in relationship with the activation type indicates that activated carbons are physically prepared in greater amounts. This tendency may be due to the fact that the best activated carbons for adsorbing of species with positive charges are those oxidized with acid functional groups. The development of these acid groups can be done via oxidation with oxygen present in the air or using some other oxidating materials such as water vapor or carbon dioxide (Dastgheib & Rockstraw, 2001). Besides, with physical activation, there is no consumption of chemical activating agents. This simplifies the preparation of activated carbons in terms of avoiding the washing procedure involved in the chemical activation and the pollution caused by this procedure. air

Figure 2. Comparison between the different types of activation and activating agents used in

H PO3

H PO3

H PO3

H PO3 H PO3

4 + H

HNO3 + Steam

KOH + (NH4

)

S

O2 8

2

KOH + CO2

ZnCl2 + CO2

K CO 2

3 + CO2

O2 2

4 + HNO3

4 +(NH4

)

S

O2 8

2

4 + CO2

4 + Air

 Physical Chemical

Physicochemical

As a result of the review done, see Figure 3, the different countries' participation in the production of activated carbon was established for this chapter. Asia is the continent with the most research done for the reduction of costs in the production of activated carbon, followed by Europe and America. In Asia, with the exception of Japan, all the countries that participated in the research can be considered underdeveloped, same as America, with the exception of the USA and Canada. It could be thought that the USA has a high degree of research because it is a leading country in terms of technological development in many areas of knowledge. Regarding Europe, it is clear its low participation in this research field. Only Spanish researchers seem to be interested in the activated carbon production problem and they have reported the use of the diverse residues generated in their country for activated carbon preparation. In Africa, because of its underdeveloped economies, only Egypt,

Even though the generalized tendency regarding the production of activated carbon leads towards the use of lignocellulosic materials, these can be produced from any carbon-based material (Girgis et al., 2002). Other non-conventional materials that have also been tested are the following: waste slurry of fertilizer plants and blast furnace waste (Gupta et al., 1997), bituminous coal (H. Teng et al., 1997, 1998), paper mill sludge (Khalili et al., 2000), bagasse fly ash (Gupta et al., 2000), waste tires (H. Teng et al., 2000), anthracite (Lillo-Ródenas et al., 2001; Lozano-Castelló et al., 2001), sewage sludge plus coconut husk (Graham et al., 2001;

the preparation of activated carbons from lignocellulosic residues.

H PO3 4 ZnCl2

KOH

NaOH

K CO 2

3

HNO3

H2SO4

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 9

0

Steam

CO2

Thermal

5

10

Publications

15

20

Algeria and Moroco participate in this research topic.

Figure 1. Lignocellulosic raw materials used in the production of activated carbon. Wood includes several varieties such as Acacia, *Eucalyptus*, fir, mahogany, olive, pine, and wattle. Almond, cedar, hazelnut, macadamia, pecan, pistachio, and, walnut are included in the nuts shells class.

Figure 2 also shows that some authors have also opted for combining activation methods. They use some of the most common chemical agents and then employ streams of diverse oxidating agents in place of inert gases.

8 Characterization Techniques and Applications in the Wastewater Treatment

al., 2006; Rodríguez-Mirasol et al., 1993). Figure 2 shows that the worldwide tendency in relationship with the activation type indicates that activated carbons are physically prepared in greater amounts. This tendency may be due to the fact that the best activated carbons for adsorbing of species with positive charges are those oxidized with acid functional groups. The development of these acid groups can be done via oxidation with oxygen present in the air or using some other oxidating materials such as water vapor or carbon dioxide (Dastgheib & Rockstraw, 2001). Besides, with physical activation, there is no consumption of chemical activating agents. This simplifies the preparation of activated carbons in terms of avoiding the washing procedure involved in the chemical activation and

Figure 1. Lignocellulosic raw materials used in the production of activated carbon. Wood includes several varieties such as Acacia, *Eucalyptus*, fir, mahogany, olive, pine, and wattle. Almond, cedar, hazelnut, macadamia, pecan, pistachio, and, walnut are included in the nuts

0 2 4 6 8 10 12 14 16 18 Publications

Figure 2 also shows that some authors have also opted for combining activation methods. They use some of the most common chemical agents and then employ streams of diverse

the pollution caused by this procedure.

Kenaf Pomegranate peel Rapeseed Seed husks of Moringa Oleifera

Seeds of Macuna mutisiana Wheat straw Mixture of apricot & peach stones

shells class.

Precursors

oxidating agents in place of inert gases.

Nuts shells

Bamboo

Orange seeds Plum kernel & stones

Peanut hull Date stones Cassava peel Cotton stalks Flamboyant pods

Vine shoot Cork waste

Rice straw & husk Sugarcane bagasse Corncob Cherry stones Peach stones & seed

Wood & sawdust Coconut shell, fibers & peel Palm fiber, pit, shell & seeds

Olive stones & cake Jute fibers & stick Mango pit (husk & seed)

Guava seed Coffe bean husk & ground Apricot stones Avocado kernel seeds & peel Grape seeds

Figure 2. Comparison between the different types of activation and activating agents used in the preparation of activated carbons from lignocellulosic residues.

As a result of the review done, see Figure 3, the different countries' participation in the production of activated carbon was established for this chapter. Asia is the continent with the most research done for the reduction of costs in the production of activated carbon, followed by Europe and America. In Asia, with the exception of Japan, all the countries that participated in the research can be considered underdeveloped, same as America, with the exception of the USA and Canada. It could be thought that the USA has a high degree of research because it is a leading country in terms of technological development in many areas of knowledge. Regarding Europe, it is clear its low participation in this research field. Only Spanish researchers seem to be interested in the activated carbon production problem and they have reported the use of the diverse residues generated in their country for activated carbon preparation. In Africa, because of its underdeveloped economies, only Egypt, Algeria and Moroco participate in this research topic.

Even though the generalized tendency regarding the production of activated carbon leads towards the use of lignocellulosic materials, these can be produced from any carbon-based material (Girgis et al., 2002). Other non-conventional materials that have also been tested are the following: waste slurry of fertilizer plants and blast furnace waste (Gupta et al., 1997), bituminous coal (H. Teng et al., 1997, 1998), paper mill sludge (Khalili et al., 2000), bagasse fly ash (Gupta et al., 2000), waste tires (H. Teng et al., 2000), anthracite (Lillo-Ródenas et al., 2001; Lozano-Castelló et al., 2001), sewage sludge plus coconut husk (Graham et al., 2001;

[3] Ahmedna, M., Marshall, W.E. & Rao, R.M. (2000). Production of granular activated carbons from select agricultural by-products and evaluation of their physical, chemical and adsorption properties. *Bioresource Technology*, Vol. 71, No. 2, (January 2000), pp.

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 11

[4] Amin, N.K. (2009). Removal of direct blue-106 dye from aqueous solution using new activated carbons developed from pomegranate peel: Adsorption equilibrium and kinetics. *Journal of Hazardous Materials*, Vol. 165, No. 1-3, (June 2009), pp. (52–62), ISSN 0304-3894. [5] Arami-Niya, A., Daud, W.M.A.W. & Mjalli, F.S. (2010). Using granular activated carbon prepared from oil palm shell by ZnCl2 and physical activation for methane adsorption. *Journal of Analytical and Applied Pyrolys*is, Vol. 89, No. 2, (November 2010), pp. (197–203),

[6] Asadullah, M., Rahman, M.A., Motin, M.A. & Sultan, M.B. (2007). Adsorption studies on activated carbon derived from steam activation of jute stick char. *Journal of Surface* 

[7] Aworn, A., Thiravetyan, P. & Nakbanpote W. (2008). Preparation and characteristics of agricultural waste activated carbon by physical activation having micro- and mesopores. *Journal of Analytical and Applied Pyrolysis*, Vol. 82, No. 2, (July 2008), pp.

[8] Bagreev, A., Bandosz, T. J. & Locke, D.L. (2001). Pore structure and surface chemistry of adsorbents obtained by pyrolysis of sewage sludge-derived fertilizer. *Carbon*, Vol. 39,

[9] Baklanova, O.N., Plaksin, G.V., Drozdov, V.A., Duplyakin, V.K., Chesnokov, N.V., Kuznetsov, B.N. (2003). Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin. *Carbon*, Vol. 41, No. 9, (June 2003), pp. (1793–1800), ISSN 0008-6223. [10] Baquero, M.C., Giraldo, L., Moreno, J.C., Suárez-García, F., Martínez-Alonso, A. & Tascón, J.M.D. (2003), Activated Carbons by pyrolysis of coffee bean husks in presence of phosphoric acid. *Analytical Applied Pyrolysis*, Vol. 70, No. 2, (December 2003) pp.

[11] Bello, G., García, R., Arriagada, R., Sepúlveda-Escribano, A., Rodríguez-Reinoso, F. (2002). Carbon molecular sieves from Eucalyptus globulus charcoal. *Microporous and Mesoporous Materials*, Vol. 56, No. 2, (November 2002), pp. (139–145), ISSN 1387-1811. [12] Bouchelta, C., Medjram, M.S., Bertrand, O. & Bellat, J.P. (2008). Preparation and characterization of activated carbon from date stones by physical activation with steam. *Journal of Analytical and Applied Pyrolysis*, Vol. 82, No. 1, (July 2008), pp. (70–77), ISSN

[13] Boudrahem, F., Aissani-Benissad, F. & Aït-Amar, H. (2009). Batch sorption dynamics and equilibrium for the removal of lead ions from aqueous phase using activated carbon developed from coffee residue activated with zinc chloride. *Journal of Environmental Management*, Vol. 90, No. 10, (July 2009), pp. (3031–3039), ISSN 0301-4797. [14] Cao, N., Darmstadt, H., Soutric, F. & Roy, Ch. (2002). Thermogravimetric study on the steam activation of charcoals obtained by vacuum and atmospheric pyrolysis of softwood

bark residues. *Carbon*, Vol. 40, No. 4, (April 2002), pp. (471–479), ISSN 0008-6223. [15] Carvalho, A.P., Gomes, M., Mestre, A.S., Pires, J. & Brotas de Carvalho, M. (2004). Activated carbons from cork waste by chemical activation with K2CO3. Application to adsorption of natural gas components. *Carbon*, Vol. 42, No. 3, (January 2004), pp. (667–

*Science & Technology*, Vol. 23, No. 1-2, pp. (73–80), ISSN 0970-1893.

No. 13, (November 2001), pp. (1971–1979), ISSN 0008-6223.

(113–123) ISSN 0960-8524.

(279–285), ISSN 0165-2370.

(779–784), ISSN 0165-2370.

0165-2370.

69), ISSN 0008-6223.

ISSN 0165-2370.

Tay et al., 2001), sewage sludge (Graham et al., 2001), sewage sludge plus peanut shell (Graham et al., 2001), sewage sludge of derived fertilizer (Bagreev et al., 2001), viscose rayon (Ko et al., 2002), corrugated paper plus silica (Okada et al., 2005), resorcinol-formaldehyde resin (Elsayed et al., 2007), cattle manure compost (Kian et al., 2008), among others.

Figure 3. Worldwide distribution and production of activated carbon obtained from lignocellulosic wastes.

#### **5. Conclusion**

The literature review (1992 – 2011) indicates that worldwide researchers try to propose new sources to obtain raw materials for the production of activated carbon. They have in mind not only to lessen its cost of production, but also to diminish environmental impact of agricultural and industrial wastes. The way to enhance the adsorptive qualities of the carbons produced is also being studied to make its production more profitable, and, hence, solve specific environmental issues.

#### **6. References**


Continent Publications

Asia 40 America 26 Europe 28 Africa 7

10 Characterization Techniques and Applications in the Wastewater Treatment

Tay et al., 2001), sewage sludge (Graham et al., 2001), sewage sludge plus peanut shell (Graham et al., 2001), sewage sludge of derived fertilizer (Bagreev et al., 2001), viscose rayon (Ko et al., 2002), corrugated paper plus silica (Okada et al., 2005), resorcinol-formaldehyde

Figure 3. Worldwide distribution and production of activated carbon obtained from

USA

Mexico

Colombia

Canada

Brazil

Chile

Cuba

Spain

Portugal

France

Bulgaria

Germany

Greece

Poland

Ukraine

UK

Egypt

Algeria

Moroco

The literature review (1992 – 2011) indicates that worldwide researchers try to propose new sources to obtain raw materials for the production of activated carbon. They have in mind not only to lessen its cost of production, but also to diminish environmental impact of agricultural and industrial wastes. The way to enhance the adsorptive qualities of the carbons produced is also being studied to make its production more profitable, and, hence,

[1] Ahmad, A.A. & Hameed, B.H. (2010). Effect of preparation conditions of activated carbon from bamboo waste for real textile wastewater. *Journal of Hazardous Materials*,

[2] Ahmad, M.A., Wan-Daud, W.M.A. & Aroua, M.K. (2007). Synthesis of carbon molecular sieves from palm shell by carbon vapor deposition. *Journal of Porous Mater*, Vol. 14, No.

Vol. 173, No. 1-3, (January 2010), pp. (487–493), ISSN 0304-3894.

4, (March 2007), pp. (393-399), ISSN 0165-2370.

lignocellulosic wastes.

Taiwan India China Malaysia Singapore Japan Thailand

0

3

6

Publications

9

12

15

Asia

America

solve specific environmental issues.

Bangladesh

 Cyprus Oman Russia Vietnam Turkey

**5. Conclusion** 

**6. References** 

resin (Elsayed et al., 2007), cattle manure compost (Kian et al., 2008), among others.

Europa

africa


[31] Giraldo, L. & Moreno-Piraján, J.C. (2007). Calorimetric determinations of activated carbons in aqueous solution. *Journal of Thermal Analysis and Calorimetry*, Vol. 89, No.2,

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 13

[32] Giraldo, L. & Moreno-Piraján, J. C. (2008). Pb2+ adsorption from aqueous solutions on activated carbons obtained from lignocellulosic residues. *Brazilian Journal of Chemical* 

[33] Girgis, B.S. & Ishak, M.F. (1999). Activated carbon from cotton stalks by impregnation with phosphoric acid. *Materials Letters*, Vol. 39, No. 2, (April 1999), pp. (107–114), ISSN

[34] Girgis, B.S., Yunis, S.S. & Soliman, A.M. (2002). Characteristics of activated carbon from peanut hulls in relation to conditions of preparation. *Materials Letters*, Vol. 57, No. 1,

[35] Graham, N., Chen, X.G. & Jayaseelan, S. (2001). The potential application of activated carbon from sewage sludge to organic dyes removal. *Water Science and Technology*, Vol.

[36] Guo, J., Gui, B., Xiang, S., Bao, X., Zhang, H., Lua, A.C. (2008). Preparation of activated carbons by utilizing solid wastes from palm oil processing mills. *Journal of Porous Mater*,

[37] Gupta, V.K., Srivastava, S.K. & Mohan, D. (1997). Equilibrium uptake, sorption dynamics, process optimization, and column operation for the removal and recovery of malachite green from wastewater using activated carbon and activated slag. *Industrial and Engineering Chemistry Research*, Vol. 36, No.6, (June 1997), pp. (2207–2218), ISSN

[38] Gupta, V.K., Mohan, D., Sharma, S. & Sharma M. (2000). Removal of basic dyes (Rhodamine B and Methylene Blue) from aqueous solution using bagasse fly ash. *Separation Science & Technology*, Vol. 35, No. 13, pp. (2097 – 2113), ISSN 0149-6395. [39] Hameed, B.H., Din, A.T.M. & Ahmad, A.L. (2007). Adsorption of methylene blue onto bamboo-based activated carbon: Kinetics and equilibrium studies. *Journal of Hazardous* 

[40] Hayashi, J., Horikawa, T., Takeda, I., Muroyama, K. & Ani, F.N. (2002). Preparing activated carbon from various nutshells by chemical activation with K2CO3. *Carbon*,

[41] Hazourli, S., Ziati, M. & Hazourli A. (2009). Characterization of activated carbon prepared from lignocellulosic natural residue:-Example of date stones-. *Physics Procedia*,

[42] Heschel, W. & Klose, E. (1995). On the suitability of agricultural by-products for the manufacture of granular activated carbon. *Fuel*, Vol. 74, No. 12, (December 1995), pp.

[43] Hu, Z., Srinivasan, M.P. & Ni, Y. (2001). Novel activation process for preparing highly microporous and meso porous activated carbons. *Carbon*, Vol. 39, No. 6 (May 2001), pp.

[44] Iniesta, E., Sánchez, F., García, A.N. & Marcilla, A. (2001).Yields and CO2 reactivity of chars from almond shells obtained by a two heating step carbonisation process. Effect of different chemical pre-treatments and ash content. *Journal of Analytical and Applied* 

*Engineering*, Vol. 25, No.1, (Jan./Mar. 2008), ISSN 0104-6632.

Vol. 15, No. 5, (December 2003), pp. (535–540), ISSN 0165-2370.

*Materials*, Vol. 141, No.3, (March 2007), pp. (819–825), ISSN 0304-3894.

Vol. 40, No. 13, (November 2002), pp. (2381-2386), ISSN 0008-6223.

*Pyrolysis*, Vol. 58–59 (April 2001), pp. (983–994), ISSN 0165-2370.

Vol. 2, No.3, pp. (1039–1043), ISSN 1875-3892.

(1786–1791), ISSN 0016-2361.

(877–886), ISSN 0008-6223.

(November 2002), pp. (164–172), ISSN 0167-577X.

43, No. 2, pp. (245–252), ISSN 0273-1223.

pp. (589–594), ISSN 1388-6150.

0167-577X.

0888-5885.


12 Characterization Techniques and Applications in the Wastewater Treatment

[16] Cossarutto, L., Zimny, T., Kaczmarczyk, J., Siemieniewska, T., Bimer, J., & Weber, J.V. (2001). Transport and sorption of water vapour in activated carbons. *Carbon,* Vol. 39,

[17] Dastgheib, S.A. & Rockstraw, D.A. (2001). Pecan shell activated carbon: synthesis, characterization, and application for the removal of copper from aqueous solution.

[18] Dávila-Jiménez, M.M., Elizalde-González, M.P. & Hernández-Montoya V. (2009). Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions. *Bioresource Technology*, Vol. 100, No.

[19] Devi, R., Singh, V. & Kumar, A. (2008). COD and BOD reduction from coffee processing wastewater using Avocado peel carbon. *Bioresource Technology*, Vol. 99, No. 1, (April

[20] Elizalde-González, M.P. & Hernández-Montoya, V. (2007). Characterization of mango pit as a raw material in the preparation of activated carbon for wastewater treatment. *Biochemical* 

[22] Elizalde-González, M.P. & Hernández-Montoya, V. (2009). Guava seed as adsorbent and as precursor of carbon for the adsorption of acid dyes. *Bioresource Technology*, Vol.

[23] Elizalde-González, M.P. & Hernández-Montoya, V. (2009). Removal of acid orange 7 by guava seed carbon: A four parameter optimization study. *Journal of Hazardous Materials*,

[24] Elizalde-González, M.P. & Hernández-Montoya, V. (2009). Use of wide-pore carbons to examine intermolecular interactions during adsorption of anthraquinone dyes from aqueous solution. *Adsorption Science & Technology,* Vol. 27, No. 5, (June 2009), pp. (447–

[25] Elizalde-González, M.P. (2006). Development of non-carbonised natural adsorbents for removal of textile dyes. *Trends in Chemical Engineering*, Vol. 10, pp. (55–66), ISSN 0972-4478. [26] Elizalde-González, M.P., Mattusch, J., Peláez-Cid, A.A. & Wennrich, R. (2007). Characterization of adsorbent materials prepared from avocado kernel seeds: Natural, activated and carbonized forms. *Journal of Analytical and Applied Pyrolysis*, Vol. 78, No. 1,

[27] Elsayed, M.A., Hall, P.J. & Heslop, M.J. (2007). Preparation and structure characterization of carbons prepared from resorcinol-formaldehyde resin by CO2

[28] Evans, M.J.B., MacDonald, J.A.F. & Halliop, E. (1999). The production of chemicallyactivated carbon. *Carbon*, Vol. 37, No. 2, (February 1999), pp. (269–274), ISSN 0008-6223. [29] Gergova, K., Petrov, N. & Minkova, V. (1993). A comparison of adsorption characteristics of various activated carbons. *Journal of Chemical Technology and* 

*Biotechnology,* Vol. 56, No. 1, (April 2007 on line), pp. (77–82), ISSN 1097-4660. [30] Gergova, K., Petrov, N. & Eser, S. (1994). Adsorption properties and microstructure of activated carbons produced from agricultural by-products by steam pyrolysis. *Carbon*,

*Engineering Journal,* Vol. 36, No. 3, (October 2007), pp. (230–238), ISSN 1369-703X. [21] Elizalde-González, M.P. & Hernández-Montoya, V. (2008). Fruit seeds as adsorbents and precursors of carbon for the removal of anthraquinone dyes. *International Journal of* 

*Chemical Engineering*, Vol. 1, No. 2-3, pp. (243-253), ISSN 0974-5793.

100, No. 7, (April 2009), pp. (2111–2117), ISSN 0960-8524.

(January 2007), pp. (185–193), ISSN 0165-2370.

activation. *Adsorption*, Vol. 13, No. 3-4, pp. (299–306).

Vol. 32, No. 4, (May 1994), pp. (693–702), ISSN 0008-6223.

Vol. 168, No. 1, (August 2009), pp. (515 – 522), ISSN 0304-3894.

*Carbon*, Vol. 39, No. 12, (October 2001), pp. (1849–1855), ISSN 0008-6223.

No. 15, (December 2001), pp. (2339–2346), ISSN 0008-6232.

24, (December 2009), pp. (6199–6206), ISSN 0960-8524.

2008), pp. (1853–1860), ISSN 0960-8524.

459), ISSN 0263-6174.


[60] Mizuta, K., Matsumoto, T., Hatate, Y., Nishihara, K. & Nakanishi, T. (2004). Removal of nitrate-nitrogen from drinking water using bamboo powder charcoal. *Bioresource* 

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 15

[61] Molina-Sabio, M., Rodríguez-Reinoso, F., Caturla, F. & Sellés, M.J. (1995). Porosity in granular carbons activated with phosphoric acid. *Carbon*, Vol. 33, No. 8, (August 1998),

[62] Molina-Sabio, M., Rodríguez-Reinoso, F., Caturla, F. & Sellés, M.J. (1996). Development of porosity in combined phosphoric acid-carbon dioxide activation. *Carbon*, Vol. 34, No.

[63] Moreno-Castilla, C., Carrasco-Marín, F., López-Ramón, M.V. & Álvarez-Merino, M.A. (2001). Chemical and physical activation of olive-mill waste water to produce activated

[65] Nabais, J.M.V., Laginhas, C.E.C., Carrott, P.J.M. & Ribeiro-Carrott M.M.L. (2011). Production of activated carbons from almond shell. *Fuel Processing Technology*, Vol. 92,

[66] Namasivayam, C. & Kavitha, D. (2002). Removal of Congo Red from water by adsorption onto activated carbon prepared from coir pith, an agricultural solid waste.

[67] Ngernyen, Y., Tangsathitkulchai, C. & Tangsathitkulchai, M. (2006). Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation. *Korean Journal of Chemical Engineering*, Vol. 23, No. 6, pp. (1046–1054), ISSN 0256-1115. [68] Okada, K., Shimizu, Y.I., Kameshima, Y. & Nakajima, A. (2005). Preparation and Properties of Carbon/Zeolite Composites with Corrugated Structure. *Journal of Porous* 

[69] Olivares-Marín, M., Fernández-González, C., Macías-García, A. & Gómez-Serrano, V. (2006). Preparation of activated carbon from cherry stones by chemical activation with ZnCl2.

[71] Ould-Idriss, A., Stitou, M., Cuerda-Correa, E.M., Fernández-González, C.A., Macías-García, A., Alexandre-Franco, M.F. & Gómez-Serrano V. (2011). Preparation of activated carbons from olive-tree wood revisited. II. Physical activation with air. *Fuel Processing* 

[72] Phan, N.H., Rio, S., Faur, C., Le Coq L., Le Cloirec, P. & Nguyen, T.H. (2006). Production of fibrous activated carbons from natural cellulose (jute, coconut) fibers for water treatment applications. *Carbon*, Vol. 44, No. 12, (October 2006), pp. (2569–2577),

[73] Puziy, A.M., Poddubnaya, O.I., Martínez-Alonso, A., Suárez-García, F. & Tascón, J.M.D. (2005). Surface chemistry of phosphorus-containing carbons of lignocellulosic origin.

*Carbon*, Vol. 43, No. 14, (November 2005), pp. (2857-2868), ISSN 0008-6223.

*Technology*, Vol. 92, No. (July 2010), pp. (266–270), ISSN 0378-3820.

*Applied Surface Science*, Vol. 252, No. 17, (June 2006), pp. (5967–5971), ISSN 0169-4332. [70] Olivares-Marín, M., Fernández-González, C., Macías-García, A. & Gómez-Serrano, V. (2006). Preparation of activated carbons from cherry stones by activation with potassium hydroxide. *Applied Surface Science*, Vol. 252, No. 17, (June 2006), pp. (5980–

*Dyes and Pigments*, Vol. 54, No. 1, (July 2002), pp. (47–58), ISSN 0143-7208 .

carbons. *Carbon*, Vol. 39, No. 9, (August 2001), pp. (1415-1420), ISSN 0008-6223. [64] Mourão, P.A.M., Laginhas, C., Custódio, F., Nabais, J.M.V., Carrott, P.J.M. & Ribeiro-Carrott M.M.L. (2011). Influence of oxidation process on the adsorption capacity of activated carbons from lignocellulosic precursors. *Fuel Processing Technology*, Vol. 92,

*Technology*, Vol. 95, No. 3, (December 2004), pp. (255–257), ISSN 0960-8524.

pp. (1105–1113), ISSN 0008-6223.

4, (April 1996), pp. (457–462), ISSN 0008-6223.

No. 2, (February 2011), pp. (241–246), ISSN 0378-3820.

No. 2, (February 2011), pp. (234–240), ISSN 0378-3820.

*Materials*, Vol. 12, No. 4, pp. (281–291), ISSN 1380-2224.

5983), ISSN 0169-4332.

ISSN 0008-6223.


14 Characterization Techniques and Applications in the Wastewater Treatment

[45] Jibril, B., Houache, O., Al-Maamari, R. & Al-Rashidi B. (2008). Effects of H3PO4 and KOH in carbonization of lignocellulosic material. Journal of Analytical and Applied

[46] Juang, R.-S., Wu F.-C. & Tseng, R.-L. (2002). Characterization and use of activated carbons prepared from bagasses for liquid-phase adsorption. *Colloids and Surfaces A*,

[47] Kalderis, D., Bethanis, S., Paraskeva, P. & Diamadopoulos, E. (2008). Production of activated carbon from bagasse and rice husk by a single-stage chemical activation method at low retention times. *Bioresource Technology*, Vol. 99, No. 15, (October 2008),

[48] Kannan, N. & Sundaram, M.M. (2001). Kinetics and mechanism of removal of methylene blue by adsorption on various carbons–a comparative study. *Dyes and* 

[49] Khalili, N.R., Campbell, M., Sandi, G. & Golas, J. (2000). Production of micro-and mesoporous activated carbon from paper mill sludge. I. Effect of zinc chloride activation. *Carbon*, Vol. 38, No. 14, (November 2000), pp. (1905–1915), ISSN 0008-6223. [50] Ko, Y.G., Choi, U.S., Kim, J.S. & Park, Y.S. (2002). Novel synthesis and characterization of activated carbon fiber and dye adsorption modeling. *Carbon*, Vol. 40, No. 14,

[51] Konstantinou, M. & Pashalidis, I. (2010). Competitive sorption of Cu(II) and Eu(III) ions on olive-cake carbon in aqueous solutions—a potentiometric study. *Adsorption,* Vol. 16,

[52] Kumar, M., Gupta, R.C. & Sharma, T. (1992). Influence of carbonisation temperature on the gasification of Acacia wood chars by carbon dioxide. *Fuel Processing Technology*, Vol.

[53] Lillo-Ródenas, M.A., Lozano-Castelló, D., Cazorla-Amorós, D. & Linares-Solano, A. (2001). Preparation of activated carbons from Spanish anthracite, II. Activation by

[54] Lozano-Castelló, D., Lillo-Ródenas, M.A., Cazorla-Amorós, D. & Linares-Solano, A. (2001). Preparation of activated carbons from Spanish anthracite, I. Activation by KOH.

[55] Lua, A.C. & Guo, J. (2000). Activated carbon prepared from oil palm stone by one-step CO2 activation for gaseous pollutant removal. *Carbon*, Vol. 38, No. 7, (June 2000), pp.

[56] Lussier, M.G., Shull, J.C. & Miller, D.J. (1994). Activated carbon from cherry stones.

[57] MacDonald, J.A.F. & Quinn, D.F. (1996). Adsorbents for methane storage made by phosphoric acid activation of peach pits. *Carbon*, Vol. 34, No. 9, (September 1996), pp.

[58] Malik, P.K. (2003). Use of activated carbons prepared from sawdust and rice husk for adsorption of acid dyes: a case study of Acid Yellow 36. *Dyes and Pigments*, Vol. 56, No.

[59] Marsh H. (Editor). (2001). *Activated carbon compendium*, Elsevier Science Ltd, ISBN: 0-08-

NaOH. *Carbon*, Vol. 39, No. 5, (April 2001), pp. (751–759), ISSN 0008-6223.

*Carbon*, Vol. 32, No. 8, (November 1994), pp. (1493–1498), ISSN 0008-6223.

*Carbon*, Vol. 39, No. 5, (April 2001), pp. (741–749), ISSN 0008-6223.

Pyrolysis, Vol. 83, No. 2, (November 2008), pp. (151–156), ISSN 0165-2370.

Vol. 201, No. 1-3, (March 2002),pp. (191–199), ISSN 0927-7757.

*Pigments*, Vol. 51, No. 1, (October 2001), pp. (25–40), ISSN 0143-7208.

(November 2000), pp. (2661–2672), ISSN 0008-6223.

No. 3, (June 2010), pp. (167–171), ISSN 10450-010-9218-1.

32, No. 1-2, (November 1992), pp. (69-76), ISSN 0378-3820.

pp. (6809–6816), ISSN 0960-8524.

(1089-1097), ISSN 0008-6223.

(1103–1108), ISSN 0008-6223.

044030-4, UK.

3, (March 2003), pp. (239–249) ISSN 0143-7208.


[88] Teng, Y.C., Lin, L.Y. & Hsu, H. (2000). Production of activated carbons from pyrolysis of waste tires impregnated with potassium hydroxide. *Journal of Air Waste Management* 

Lignocellulosic Precursors Used in the Elaboration of Activated Carbon 17

[89] Toles, C.A., Marshall, W.E., Johns, M.M. (1997). Granular activated carbons from nutshells for the uptake of metals and organic compounds. *Carbon*, Vol. 35, No. 9,

[90] Tsai, W.T., Chang, C.Y. & Lee, S.L. (1997). Preparation and characterization of activated carbons from corn cob. *Carbon.* Vol. 35, No. 8, (November 1997), pp. (1198–1200), ISSN

[91] Tsai, W.T., Chang, C.Y. & Lee, S.L. (1998). A low cost adsorbent from agricultural waste corn cob by zinc chloride activation. *Bioresource Technology*, Vol. 64, No. 3, (June 1998),

[92] Tsai, W.T., Chang, C.Y., Lin, M.C., Chien, S.F., Sun, H.F. & Hsieh, M.F. (2001a). Adsorption of acid dye onto activated carbons prepared from agricultural waste bagasse by ZnCl2 activation. *Chemosphere,* Vol. 45, No. 1, (October 2001), pp. (51–58),

[93] Tsai, W.T., Chang, C.Y., Wang, S.Y., Chang, C.F., Chien, S.F. & Sun, H.F. (2001b). Preparation of activated carbons from corn cob, catalyzed by potassium salts and subsequent gasification with CO2, *Bioresource Technology*, Vol. 78, No. 2, (June 2001), pp.

[94] Tsai, W.T., Chang, C.Y., Wang, S.Y., Chang, C.F., Chien, S.F. & Sun, H.F. (2001c). Cleaner production of carbon adsorbents by utilizing agricultural waste corn cob. *Resources,* 

[96] Valente-Nabais, J.M., Gomes, J.A., Suhas, Carrott, P.J.M., Laginhas, C. & Roman, S. (2009). Phenol removal onto novel activated carbons made from lignocellulosic precursors: influence of surface properties, *Journal of Hazardous Materials*, Vol. 167, No.

[97] Vargas, A.M.M., Cazetta, A.L., Garcia, C.A., Moraes, J.C.G., Nogami, E.M., Lenzi, E., Costa, W.F. & Almeida, V.C. (2011). Preparation and characterization of activated carbon from a new raw lignocellulosic material: flamboyant (*Delonix Regia*) pods. *Journal of Environmental Management*, Vol. 92, No. 1, (January 2011), pp. (178-184), ISSN 0301-4797. [98] Vargas, J.E., Giraldo, L. & Moreno-Piraján, J.C. (2010). Preparation of activated carbons from seeds of Macuna mutisiana by physical activation with steam. *Journal of Analytical and Applied Pyrolisis*, Vol. 89, No. 2, (November 2010), pp. (307-312), ISSN 0165-2370. [99] Warhurst, A.M., Fowler, G.D., McConnachie, G.L. & Pollard, S.J.T. (1997). Pore structure and adsorption characteristics of steam pyrolysis carbons from *Moringa* 

*oleifera*. *Carbon*, Vol. 35, No. 8, (August 1997), pp. (1039–1045), ISSN 0008-6223. [100] Wu, F.C., Tseng, R.L. & Juang, R.S. (1999). Pore structure and adsorption performance of the activated carbons prepared from plum kernels. *Journal of Hazardous Materials*, Vol.

[101] Wu, F.C., Tseng, R.L. & Juang, R.S. (2001). Adsorption of dyes and phenol from water on the activated carbons prepared from corncob wastes. *Environmental Technology*, Vol.

*Conservation and Recycling*, Vol. 32, No. 1, (May 2001), pp. (43–53), ISSN 0921-3449. [95] Tseng, R.-L. & Tseng, S.-K. (2005). Pore structure and adsorption performance of the KOH-activated carbons prepared from corncob. *Journal of Colloid and Interface Science*,

Vol. 287, No. 2, (July 2005), pp. (428–437), ISSN 0021-9797.

69, No. 3, (November 1999), pp. (287–302), ISSN 0304-3894.

22, No. 2, (February 2001), pp. (205–213), ISSN 0959-3330.

1-3, (August 2009), pp. (904–910), ISSN 0304-3894.

*Association*, Vol. 50, (November 2000), pp. (1940–1946), ISSN 1047-3289.

(September 1997), pp. (1407-1414), ISSN 0008-6223.

0008-6223.

ISSN 0045-6535.

pp. (211–217), ISSN 0960-8524.

(203–208), ISSN 0960-8524.


16 Characterization Techniques and Applications in the Wastewater Treatment

[74] Qian, Q., Machida, M., Aikawa, M. & Tatsumoto, H. (2008). Effect of ZnCl2 impregnation ratio on pore structure of activated carbons prepared from cattle manure compost: Application of N2 adsorption desorption isotherms. *Journal of Material Cycles* 

[75] Rajeshwarisivaraj, Sivakumar, S., Senthilkumar, P. & Subburam, V. (2001). Carbon from Cassava peel, an agricultural waste, as an adsorbent in the removal of dyes and metal ions from aqueous solution. *Bioresource Technology*, Vol. 80, No. 3, (December 2001), pp.

[76] Robau-Sánchez, A., Aguilar-Elguézabal, A. & De La Torre-Saenz, L. (2001). CO2 activation of char from quercus agrifolia wood waste. *Carbon*, Vol. 39, No. 9, (August

[77] Robinson, T., McMullan, G., Marchant, R & Nigam, P. (2001). Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative,

[78] Rodríguez-Mirasol, J., Cordero, T. & Rodríguez J.J. (1993). Preparation and characterization of activated carbons from eucalyptus kraft lignin. *Carbon*, Vol. 31, No.

[79] Rodríguez-Reinoso, R. & Molina-Sabio, M. (1992), Activated carbons from lignocellulosic materials by chemical and/or physical activation: An overview. *Carbon*,

[80] Salame, I.I. & Bandosz, T.J. (2001). Surface chemistry of Activated Carbons: Combining the results of Temperature-Programmed Desorption, Boehm and Potentiometric Titrations. *Journal of Colloids and Interface Science*, Vol. 240, No. 1, (August 2001), pp.

[81] Salunkhe, D.K., & Kadam, S.S. (Editors). (1995). *Handbook of fruit science and technology, production, composition, storage and processing*, Marcel Dekker, Inc., ISBN: 0-8247-9643-8, USA. [82] Senthilkumaar, S., Kalaamani, P., Porkodi, K., Varadarajan, P.R. & Subburaam, C.V. (2006). Adsorption of dissolved Reactive red dye from aqueous phase onto activated carbon prepared from agricultural waste. *Bioresource Technology,* Vol. 97, No. 14,

[83] Sun, R.Q., Sun, L.B., Chun, Y. & Xu, Q.H. (2008). Catalytic performance of porous carbons obtained by chemical activation. *Carbon*, Vol. 46, No. 13, (November 2008), pp.

[84] Swarnalatha, S., Ganesh-Kumar, A. & Sekaran, G. (2009). Electron rich porous carbon/silica matrix from rice husk and its characterization. *Journal of Porous Mater*, Vol.

[85] Tay, J.H., Chen, X.G., Jeyaseelan, S. & Graham, N. (2001). Optimising the preparation of activated carbon from digested sewage sludge and coconut husk. *Chemosphere*, Vol. 44,

[86] Teng, H., Ho, J.A. & Hsu, Y.F. (1997). Preparation of activated carbons from bituminous coals with CO2 activation-influence of coal oxidation. *Carbon*, Vol. 35, No. 2, (February

[87] Teng, H., Yeh, T.S. & Hsu, L.Y. (1998). Preparation of activated carbon from bituminous coals with phosphoric acid activation. *Carbon*, Vol. 36, No. 9, (September 1998), pp.

*Bioresource Technology*, Vol. 77, No. 3, (May 2001), pp. (247–255), ISSN 0960-8524.

*Waste Management*, Vol. 10, No. 1, pp. (53–61), ISSN 1438-4957.

Vol. 30, No. 7, (October 1992), pp. (1111–1118), ISSN 0008-6223.

(233–235), ISSN 0960-8524.

(252–258), ISSN 0021-9797.

(1757–1764) ISSN 0008-6223.

16, No. 3, pp. (239–245), ISSN 1380-2224.

1997), pp. (275–283), ISSN 0008-6223.

(1387–1395), ISSN 0008-6223.

No. 1, (July 2001), pp. (45–51), ISSN 0045-6535.

2001), pp. (1367–1377) ISSN 0008-6223.

1, (January 1993), pp. (87–95), ISSN 0008-6223.

(September 2006), pp. (1618–1625), ISSN 0960-8524.


[102] Yavuz, R.; Akyildiz, H.; Karatepe, N. & Çetinkaya, E. (2010). Influence of preparation conditions on porous structures of olive stone activated by H3PO4. Fuel Processing Technology, Vol. 91, No. 1, (January 2010), pp. (80–87), ISSN 0378-3820.

**2** 

*México* 

*Instituto Tecnológico de Aguascalientes* 

**Thermal Treatments and Activation Procedures** 

Virginia Hernández-Montoya, Josafat García-Servin and José Iván Bueno-López

The preparation of activated carbons (ACs) generally comprises two steps, the first is the carbonization of a raw material or precursor and the second is the carbon activation. The carbonization consists of a thermal decomposition of raw materials, eliminating non-carbon species and producing a fixed carbon mass with a rudimentary pore structure (very small and closed pores are created during this step). On the other hand, the purpose of activation is to enlarge the diameters of the small pores and to create new pores and it can be carried out by chemical or physical means. During chemical activation, carbonization and activation are accomplished in a single step by carrying out thermal decomposition of the raw material impregnated with certain chemical agents such as H3PO4, H2SO4, HNO3, NaOH, KOH and ZnCl2 (Hu et al., 2001; Mohamed et al., 2010). Physical or thermal activation uses an oxidizing gas (CO2, steam, air, etc.) for the activation of carbons after carbonization, in the temperature range from 800 to 1100 ºC. The carbonization can be carried out using tubular furnaces, reactors, muffle furnace and, more recently, in glass reactor placed in a modified microwave oven (Foo & Hameed, 2011; Tongpoothorn et al., 2011; Vargas et al., 2010).

Nowadays, the raw materials more used in the preparation of carbons are of lignocellulosic origin. Wood and coconut shells are the major precursors and responsible for the world production of more than 300, 000 tons/year of ACs (Mouräo et al., 2011). However, the precursor selection depends of their availability, cost and purity, but the manufacturing process and the application of the product are also important considerations (Yavuz et al., 2010). Figure 1 shows the number of publications studied in this chapter, related with the preparation of activated carbons from lignocellulosic materials in last two decades. A clear trend can be observed: the number of works increased in the years from 2000 to 2010. The

In the present chapter the principal methods used in the preparation of activated carbons from lignocellulosic materials by chemical and physical procedures are discussed. An analysis of the experimental conditions used in the synthesis of ACs has been made attending to the carbon specific surface area. Also the advantages and disadvantages of each

obtained carbons were mainly employed in the removal of water pollutants.

**1. Introduction** 

method are discussed.

**Used in the Preparation of Activated Carbons** 


## **Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons**

Virginia Hernández-Montoya, Josafat García-Servin and José Iván Bueno-López *Instituto Tecnológico de Aguascalientes México* 

#### **1. Introduction**

[102] Yavuz, R.; Akyildiz, H.; Karatepe, N. & Çetinkaya, E. (2010). Influence of preparation conditions on porous structures of olive stone activated by H3PO4. Fuel Processing

[103] Zhang, H., Yan, Y. & Yang, L. (2010). Preparation of activated carbon from sawdust by zinc chloride activation. *Adsorption*, Vol. 16, No. 3, (August 2010), pp. (161–166). [104] Zuo, S., Yang, J. & Liu, J. (2010). Effects of the heating history of impregnated lignocellulosic material on pore development during phosphoric acid activation.

Technology, Vol. 91, No. 1, (January 2010), pp. (80–87), ISSN 0378-3820.

*Carbon*, Vol. 48, No. 11, (September 2010), pp. (3293–3295), ISSN 0008-6223.

The preparation of activated carbons (ACs) generally comprises two steps, the first is the carbonization of a raw material or precursor and the second is the carbon activation. The carbonization consists of a thermal decomposition of raw materials, eliminating non-carbon species and producing a fixed carbon mass with a rudimentary pore structure (very small and closed pores are created during this step). On the other hand, the purpose of activation is to enlarge the diameters of the small pores and to create new pores and it can be carried out by chemical or physical means. During chemical activation, carbonization and activation are accomplished in a single step by carrying out thermal decomposition of the raw material impregnated with certain chemical agents such as H3PO4, H2SO4, HNO3, NaOH, KOH and ZnCl2 (Hu et al., 2001; Mohamed et al., 2010). Physical or thermal activation uses an oxidizing gas (CO2, steam, air, etc.) for the activation of carbons after carbonization, in the temperature range from 800 to 1100 ºC. The carbonization can be carried out using tubular furnaces, reactors, muffle furnace and, more recently, in glass reactor placed in a modified microwave oven (Foo & Hameed, 2011; Tongpoothorn et al., 2011; Vargas et al., 2010). raw

Nowadays, the raw materials more used in the preparation of carbons are of lignocellulosic origin. Wood and coconut shells are the major precursors and responsible for the world production of more than 300, 000 tons/year of ACs (Mouräo et al., 2011). However, the precursor selection depends of their availability, cost and purity, but the manufacturing process and the application of the product are also important considerations (Yavuz et al., 2010). Figure 1 shows the number of publications studied in this chapter, related with the preparation of activated carbons from lignocellulosic materials in last two decades. A clear trend can be observed: the number of works increased in the years from 2000 to 2010. The obtained carbons were mainly employed in the removal of water pollutants.

In the present chapter the principal methods used in the preparation of activated carbons from lignocellulosic materials by chemical and physical procedures are discussed. An analysis of the experimental conditions used in the synthesis of ACs has been made attending to the carbon specific surface area. Also the advantages and disadvantages of each method are discussed. 

precursor is carbonized under an inert atmosphere, and the resulting carbon is subjected to a partial and controlled gasification at high temperature (Rodriguez–Reinoso & Molina-

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 21

In the following sections the principal characteristics of the procedures used in the preparation of activated carbons from lignocellulosic precursors by physical and chemical

The carbonization step and the activation step simultaneously progress in the chemical activation (Hayashi et al., 2002a). In this case, the lignocellulosic precursor is treated primarily with a chemical agent, such as H3PO4, H2SO4, HNO3, NaOH, KOH or ZnCl2 by impregnation or physical mixture and the resulting precursor is carbonized at temperatures between 400 and 800 ºC under a controlled atmosphere. The function of the dehydrating agents is to inhibit the formation of tar and other undesired products during the carbonization process. Also, the pore size distribution and surface area are determined by the ratio between the mass of the chemical agent and the raw material. Besides, activation time, carbonization temperature and heating rate are important preparation variables for obtaining ACs with specific characteristics (Mohamed et al., 2010). The effects of all these parameters in the textural characteristics of ACs employing different activating agents are

In the last 20 years, the activation of lignocellulosic materials with H3PO4 has become an increasingly used method for the large-scale manufacture of ACs because the use of this reagent has some environmental advantages such as ease of recovery, low energy cost and high carbon yield. H3PO4 plays two roles during the preparation of ACs: i) H3PO4 acts as an acid catalyst to promote bond cleavage, hydrolysis, dehydration and condensation, accompanied by cross-linking reactions between phosphoric acid and biopolymers; ii) H3PO4 may function as a template because the volume occupied by phosphoric acid in the interior of the activated precursor is coincident with the micropore volume of the activated

The chemical and physical properties of ACs obtained by chemical activation with H3PO4 are affected by the experimental conditions of preparation such as acid concentration, time of activation, impregnation ratio, carbonization temperature and heating rate. Also some recent works have shown that the atmosphere used in the carbonization process has an obvious effect on the physicochemical properties of ACs (Zuo et al., 2009). Table 1 collects some experimental conditions used in the preparation of activated carbons from

Sabio, 1992).

methods are described.

**2.1 Chemical activation** 

discussed in the following sections.

**2.1.1 Phosphoric acid (H3PO4)** 

carbon obtained (Zuo et al., 2009).

lignocellulosic materials using N2 as activation atmosphere.

Figure 1. Number of publications related with the preparation of activated carbons from lignocellulosic precursors in the last two decades

#### **2. Preparation of activated carbons**

The preparation of ACs from lignocellulosic materials involved two processes, the carbonization and the activation, which can be performed in one or two steps depending on the activation method (physical or chemical, respectively). Specifically, when the carbonization is carried out in an inert atmosphere the process is called *pyrolysis*. According to the literature, the pyrolysis of lignocellulosic materials as coconut shells, olive stones, walnut shells, etc., gives rise to three phases: the char, oils (tars) and gases. The relative amount of each phase is a function of parameters such as temperature of pyrolysis, nitrogen flow rate and heating rate. For example, slow heating rates promote high yields of the carbon residue while flash pyrolysis is recommended for high liquid (oil) ratios (Mohamed et al., 2010). stones, Besides, carbonization

During the pyrolysis of lignocellulosic precursors, a rudimentary porosity is obtained on the char fraction as a consequence of the release of most of the non-carbon elements such as hydrogen, oxygen and nitrogen in form of gases and tars, leaving a rigid carbon skeleton formed by aromatic structures.

There are two conventional methods for activating carbons: physical (or thermal) and chemical activation. During the chemical activation, the precursor is first impregnated or physically mixed with a chemical compound, generally a dehydrating agent. The impregnated carbon or the mixture is then heated in an inert atmosphere (Moreno-Castilla et al., 2001). On the other hand, during a physical activation process the lignocellulosic precursor is carbonized under an inert atmosphere, and the resulting carbon is subjected to a partial and controlled gasification at high temperature (Rodriguez–Reinoso & Molina-Sabio, 1992). resulting

In the following sections the principal characteristics of the procedures used in the preparation of activated carbons from lignocellulosic precursors by physical and chemical methods are described.

#### **2.1 Chemical activation**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

20 Characterization Techniques and Applications in the Wastewater Treatment

Figure 1. Number of publications related with the preparation of activated carbons from

1985 1990 1995 2000 2005 2010

Year

The preparation of ACs from lignocellulosic materials involved two processes, the carbonization and the activation, which can be performed in one or two steps depending on the activation method (physical or chemical, respectively). Specifically, when the carbonization is carried out in an inert atmosphere the process is called *pyrolysis*. According to the literature, the pyrolysis of lignocellulosic materials as coconut shells, olive stones, walnut shells, etc., gives rise to three phases: the char, oils (tars) and gases. The relative amount of each phase is a function of parameters such as temperature of pyrolysis, nitrogen flow rate and heating rate. For example, slow heating rates promote high yields of the carbon residue while flash pyrolysis is recommended for high liquid (oil) ratios (Mohamed

During the pyrolysis of lignocellulosic precursors, a rudimentary porosity is obtained on the char fraction as a consequence of the release of most of the non-carbon elements such as hydrogen, oxygen and nitrogen in form of gases and tars, leaving a rigid carbon skeleton

There are two conventional methods for activating carbons: physical (or thermal) and chemical activation. During the chemical activation, the precursor is first impregnated or physically mixed with a chemical compound, generally a dehydrating agent. The impregnated carbon or the mixture is then heated in an inert atmosphere (Moreno-Castilla et al., 2001). On the other hand, during a physical activation process the lignocellulosic

lignocellulosic precursors in the last two decades

**2. Preparation of activated carbons** 

0

2

4

6

Publications

8

10

12

et al., 2010).

formed by aromatic structures.

The carbonization step and the activation step simultaneously progress in the chemical activation (Hayashi et al., 2002a). In this case, the lignocellulosic precursor is treated primarily with a chemical agent, such as H3PO4, H2SO4, HNO3, NaOH, KOH or ZnCl2 by impregnation or physical mixture and the resulting precursor is carbonized at temperatures between 400 and 800 ºC under a controlled atmosphere. The function of the dehydrating agents is to inhibit the formation of tar and other undesired products during the carbonization process. Also, the pore size distribution and surface area are determined by the ratio between the mass of the chemical agent and the raw material. Besides, activation time, carbonization temperature and heating rate are important preparation variables for obtaining ACs with specific characteristics (Mohamed et al., 2010). The effects of all these parameters in the textural characteristics of ACs employing different activating agents are discussed in the following sections.

#### **2.1.1 Phosphoric acid (H3PO4)**

In the last 20 years, the activation of lignocellulosic materials with H3PO4 has become an increasingly used method for the large-scale manufacture of ACs because the use of this reagent has some environmental advantages such as ease of recovery, low energy cost and high carbon yield. H3PO4 plays two roles during the preparation of ACs: i) H3PO4 acts as an acid catalyst to promote bond cleavage, hydrolysis, dehydration and condensation, accompanied by cross-linking reactions between phosphoric acid and biopolymers; ii) H3PO4 may function as a template because the volume occupied by phosphoric acid in the interior of the activated precursor is coincident with the micropore volume of the activated carbon obtained (Zuo et al., 2009).

The chemical and physical properties of ACs obtained by chemical activation with H3PO4 are affected by the experimental conditions of preparation such as acid concentration, time of activation, impregnation ratio, carbonization temperature and heating rate. Also some recent works have shown that the atmosphere used in the carbonization process has an obvious effect on the physicochemical properties of ACs (Zuo et al., 2009). Table 1 collects some experimental conditions used in the preparation of activated carbons from lignocellulosic materials using N2 as activation atmosphere.

Figure 2. Specific surface area of activated carbons obtained by chemical activation of

Jackfruit peel waste

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 23

Almond shell

Oil palm shell

Pistachio-nut shells

Licorice residues

shells

Sea-buckthorn stones

China fir

Olive stone

Avocado kernel seed

Chemical activation of lignocellulosic materials with ZnCl2 leads to the production of activated carbons with good yield a well-developed porosity in only one step. Impregnation with ZnCl2 first results in degradation of the material and, on carbonization, produces dehydration that results in charring and aromatization of the carbon skeleton and creation of the pore structure (Caturla et al., 1991). In this case, the precursor is impregnated with a concentrated ZnCl2 solution during a given contact time, followed by evaporation of the solution and, finally, the precursor is carbonized in an inert atmosphere and thoroughly washed to extract the excess of ZnCl2. The amount of ZnCl2 incorporated in the precursor and the temperature of heat treatment are the two variables with a direct incidence in the development of the porosity. Table 2 shows the experimental conditions used in the preparation of ACs by chemical activation with ZnCl2 using N2 as activation atmosphere.

The specific surface areas of the carbons reported in the papers of Table 2 are shown in Figure 3. Carbons obtained using the highest impregnation ratios (2 and 2.5) and an activation temperature of 800 ºC are the materials with the largest SBET (Caturla et al., 1991; Hu et al., 2001). The carbon obtained from coconout shells reaches an SBET value of 2400 m2 g-1, whereas for the carbon prepared from peach stones the SBET was 2000 m2 g-1. Other carbons prepared from coconut shells using an impregnation ratio of 1 and an activation temperature of 500 ºC show lower specific surface areas (1200 m2 g-1). In any case, all the carbons prepared by chemical activation with ZnCl2 attain SBET greater than 750 m2 g-1 (Azevedo et al., 2007). The principal disadvantage of this activation is the environmental

lignocellulosic materials with H3PO4 (black bars: ACs with greater SBET)

Tea plant

Pine wood

Pecan shell

Stem of date palm

**2.1.2 Zinc Chloride (ZnCl2)** 

Fruit stones

0

500

1000

Specific surface (m2 g-1

)

1500

2000

Jute

 H3 PO4

Coconut Fibers

Olive-mill waste water

risks related to zinc compounds.


Table 1. Experimental conditions of activated carbons obtained by chemical activation with H3PO4 using different lignocellulosic precursors carbons obtained

In most of the cited papers, the concentration of acid is greater than 50% (w/w) and the activation temperature for 75 % of these studies is between 350 and 600 ºC (see Table 1). Figure 2 shows the specific surface area calculated by the Brunauer, Emmett and Teller method (SBET) of the ACs prepared in the contributions collected in Table 1. Carbons obtained with the highest phosphoric impregnation ratio (China Fir and avocado kernel seeds) are the materials with the largest SBET (1785 and 1802 m2 g-1). Additionally, the carbon obtained from Oil palm shell and activated using a rather low impregnation ratio (0.09) was one of the materials with a lower specific surface area (356 m2 g-1).

Figure 2. Specific surface area of activated carbons obtained by chemical activation of lignocellulosic materials with H3PO4 (black bars: ACs with greater SBET)

#### **2.1.2 Zinc Chloride (ZnCl2)**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

Heating rate (ºC min-1)

Reference

(2007)

(2008)

(2010)

(2011)

(2010)

(2000)

(2007)

(2010)

(2008)

al. (2010)

et al. (2001)

González et al.

22 Characterization Techniques and Applications in the Wastewater Treatment

(ºC)

China fir 50 4.6 475 5 Zuo et al. (2009)

Fruit stones 60 1.02 800 - Puziy et al. (2005)

Jute 30 4 900 20 Phan et al. (2006)

Oil palm shell 85 0.09 450 5 Arami-Niya et al.

Olive waste 75 2.4 500 10 Moreno-Castilla

Pecan shell 50 - 450 - Ahmedna et al.

Pine Wood 85 1.5 400 - Hared et al.

Tea plant 85 3 350 - Yagmur et al.

10 et plant chemical

Table 1. Experimental conditions of activated carbons obtained by chemical activation with

In most of the cited papers, the concentration of acid is greater than 50% (w/w) and the activation temperature for 75 % of these studies is between 350 and 600 ºC (see Table 1). Figure 2 shows the specific surface area calculated by the Brunauer, Emmett and Teller method (SBET) of the ACs prepared in the contributions collected in Table 1. Carbons obtained with the highest phosphoric impregnation ratio (China Fir and avocado kernel seeds) are the materials with the largest SBET (1785 and 1802 m2 g-1). Additionally, the carbon obtained from Oil palm shell and activated using a rather low impregnation ratio (0.09) was

Olive Stone 50 2 400 5 Yavuz et al.

85 6 800 5 Elizalde-

30 4 900 20 Phan et al. (2006)

85 4 550 - Prahas et al.

89 1.5 400 2.5 Kaghazchi et al.

89 0.5 400 5 Kaghazchi et al.

5 Moreno-Castilla Ahmedna 1.5

85 0.5 550 10 Mohammadi et

85 5 600 10 Jibril et al. (2008)

Activation temperature

Impregnation

ratio

Precursor H3PO4

Avocado kernel seed

Coconut Fibers

Licorice residues

Jackfruit peel waste

Pistachio-nut

Sea-buckthorn

Stem of date palm

H3PO4 using different lignocellulosic precursors

one of the materials with a lower specific surface area (356 m2 g-1).

shells

stones

(%)

Chemical activation of lignocellulosic materials with ZnCl2 leads to the production of activated carbons with good yield a well-developed porosity in only one step. Impregnation with ZnCl2 first results in degradation of the material and, on carbonization, produces dehydration that results in charring and aromatization of the carbon skeleton and creation of the pore structure (Caturla et al., 1991). In this case, the precursor is impregnated with a concentrated ZnCl2 solution during a given contact time, followed by evaporation of the solution and, finally, the precursor is carbonized in an inert atmosphere and thoroughly washed to extract the excess of ZnCl2. The amount of ZnCl2 incorporated in the precursor and the temperature of heat treatment are the two variables with a direct incidence in the development of the porosity. Table 2 shows the experimental conditions used in the preparation of ACs by chemical activation with ZnCl2 using N2 as activation atmosphere.

The specific surface areas of the carbons reported in the papers of Table 2 are shown in Figure 3. Carbons obtained using the highest impregnation ratios (2 and 2.5) and an activation temperature of 800 ºC are the materials with the largest SBET (Caturla et al., 1991; Hu et al., 2001). The carbon obtained from coconout shells reaches an SBET value of 2400 m2 g-1, whereas for the carbon prepared from peach stones the SBET was 2000 m2 g-1. Other carbons prepared from coconut shells using an impregnation ratio of 1 and an activation temperature of 500 ºC show lower specific surface areas (1200 m2 g-1). In any case, all the carbons prepared by chemical activation with ZnCl2 attain SBET greater than 750 m2 g-1 (Azevedo et al., 2007). The principal disadvantage of this activation is the environmental risks related to zinc compounds.

Figure 3. Specific surface area of activated carbons obtained by chemical activation of

Alkaline hidroxides (KOH, NaOH) and carbonates (K2CO3, Na2CO3) have been used as activation reagents in the preparation of activated carbons with high specific surface. In general terms, chemical activation by KOH and NaOH consists in a solid-solid or solidliquid reaction involving the hydroxide reduction and carbon oxidation to generate porosity (Adinata et al., 2007). The activation with KOH was first reported in the late 1970s by AMOCO Corporation; since then many studies have been devoted to the preparation of ACs by chemical activation with KOH (Lua & Yang, 2004). In this context, two procedures have been used. The carbon precursor can be mixed with powder of KOH or impregnated with a concentrated solution of KOH and then the solid mixture or impregnated precursor is thermally treated under nitrogen (Bagheri & Abedi, 2009; Moreno-Castilla et al., 2001). Alternatively, the preparation of ACs by alkaline activation is made in two steps, in which the precursor is first pyrolyzed and the obtained carbon is activated with a solution of KOH (Bagheri & Abedi, 2009) or with pellets of KOH and finally thermally treated again. The activation step can be conducted in a glass reactor placed in a modified micro wave oven

Sodium hidroxide has been also shown to be more interesting activation agent due to the possibility of reducing chemical activation costs and environmental load when compared with KOH activation (Tongpoothorn et al., 2011). The activation procedure with NaOH is

lignocellulosic materials with ZnCl2 (black bars: ACs with greater SBET)

Coir Pith

Oil palm shells

Coffee residue

coconut shells

Walnut shells

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 25

Oil palm shell

 shells

residues

Cherry stones

Coconut shells

Peach stones

Sea-buckthorn stones

Licorice

Pistachio-nut

with a frequency of 2.45 GHz (Foo & Hameed, 2011).

similar to KOH (Tseng, 2007; Vargas et al., 2011).

**2.1.3 Alkalis** 

Almond shells

0

500

1000

1500

Specific surface (m2 g-1

)

2000

2500 ZnCl2

Sargassum longifolium

Hypnea valentiae


Table 2. Experimental conditions of activated carbons obtained by chemical activation with ZnCl2 using different lignocellulosic precursors obtained

Figure 3. Specific surface area of activated carbons obtained by chemical activation of lignocellulosic materials with ZnCl2 (black bars: ACs with greater SBET)

#### **2.1.3 Alkalis**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

Heating rate (ºC min-1)

Reference

al. (2006)

(2007)

(2009)

(2009)

(2010)

(2011)

(2010)

(1991)

(2010)

(2009)

(2010)

Kadirvelu (1997)

&Martín (1991)

24 Characterization Techniques and Applications in the Wastewater Treatment

Coir Pith 1 700 - Namasivayam &

Peach stones 2.5 800 - Caturla et al.

2 600 - Torregrosa

3 500 10 Olivares-Marín et

1 500 4 Azevedo et al.

2 800 10 Hu et al. (2001)

1 600 10 Boudrahem et al.


1 500 2.5 Kaghazchi et al.



1.5 500 5 Kaghazchi et al.


0.5 550 - Mohammadi et al.

2 450 5 Yang & Qiu (2010)

Table 2. Experimental conditions of activated carbons obtained by chemical activation with

Activation temperature (ºC)

Precursor Impregnation

Almond shells

Cherry stones

Coconut shells

Coconut shells\*

Coffee residue

Hypnea valentiae

Licorice residues

Oil palm shell

Oil palm shells

Pistachio-nut

Sargassum longifolium

longifolium

shells

Seabuckthorn stones

Walnut shells

ZnCl2 using different lignocellulosic precursors

ratio (IR)

Alkaline hidroxides (KOH, NaOH) and carbonates (K2CO3, Na2CO3) have been used as activation reagents in the preparation of activated carbons with high specific surface. In general terms, chemical activation by KOH and NaOH consists in a solid-solid or solidliquid reaction involving the hydroxide reduction and carbon oxidation to generate porosity (Adinata et al., 2007). The activation with KOH was first reported in the late 1970s by AMOCO Corporation; since then many studies have been devoted to the preparation of ACs by chemical activation with KOH (Lua & Yang, 2004). In this context, two procedures have been used. The carbon precursor can be mixed with powder of KOH or impregnated with a concentrated solution of KOH and then the solid mixture or impregnated precursor is thermally treated under nitrogen (Bagheri & Abedi, 2009; Moreno-Castilla et al., 2001). Alternatively, the preparation of ACs by alkaline activation is made in two steps, in which the precursor is first pyrolyzed and the obtained carbon is activated with a solution of KOH (Bagheri & Abedi, 2009) or with pellets of KOH and finally thermally treated again. The activation step can be conducted in a glass reactor placed in a modified micro wave oven with a frequency of 2.45 GHz (Foo & Hameed, 2011).

Sodium hidroxide has been also shown to be more interesting activation agent due to the possibility of reducing chemical activation costs and environmental load when compared with KOH activation (Tongpoothorn et al., 2011). The activation procedure with NaOH is similar to KOH (Tseng, 2007; Vargas et al., 2011).

Precursor Activating

Coffee endocarp

Olive-mill waste water

shell

Pistachio nut

Pistachio nut shell\*

Soybean oil cake

Stem of date palm

*NaOH*

*K2CO3* Chickpea husk

Pistachio shell

Soybean oil cake

Jatropha curcas

state

IR Carbonization

Solution 1.75 Frequency of 2.45 GHz.

temperature (ºC)

Corn cobs Solution 2 550 10 Bagheri & Abedi

*KOH* Cassava peel - 2.5 750 10 Sudaryanto et al.

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 27

Powder 1:2 850 5 Nabais et al. (2008)

Solution 2 800 10 Moreno-Castilla et

Pellets 0.5 300 10 Lua & Yang (2004)

Solution 0.95 800 5 Tay et al. (2009)

Solution 3 600 50 Jibril et al. (20089

Solution 4 400 - Tongpoothorn et al.

Solution - 800 10 Hayashi et al.

Solution - 800 10 Hayashi et al.

Solution 1 800 5 Tay et al. (2009)

Flamboyant Pellets 3 700 20 Vargas et al. (2011)

Plum kernels Solution 4 780 - Tseng (2007)

Cork waste Solution 3 800 10 Carvalho et al.

Palm shell Solution 2 800 10 Adinata et al.

Waste apricot Solution 1 900 10 Erdoğan et al.

NaOH and KOH using different lignocellulosic precursors

Table 3. Experimental conditions of activated carbons obtained by chemical activation with

Heating rate (ºC min-1)

Reference

(2006)

(2009)

(2011)

(2002b)

(2004)

(2007)

(2002a)

(2005)

600 W Foo & Hameed (2011)

al. (2001)

In general, the preparation of ACs by chemical activation with KOH and NaOH allows to obtain carbons with high specific surface areas (>1000 m2 g-1). However, KOH and NaOH are corrosive and deleterious chemicals (Hayashi et al., 2002a). For this reason, recent studies have proposed the preparation of activated carbons by chemical activation with K2CO3 in one step, in which the lignocellulosic materials is impregnated with a K2CO3 solution and finally the impregnated precursor is thermally treated. K2CO3 is a not deleterious reagent and it is broadly used for food additives (Hayashi et al., 2002a).

Table 3 summarizes the experimental conditions used in the preparation of ACs from lignocellulosic materials by chemical activation with NaOH, KOH and K2CO3. Carbons obtained by activation with NaOH are the materials showing higher SBET (see Figure 4), for example, the carbon obtained from flamboyant exhibiting a SBET near to 2500 m2 g-1. Also, the activation with K2CO3 renders carbons with a competitive SBET (between 1200 and 1800 m2 g-1) compared with those obtained by activation with KOH or NaOH.

Other interesting observation is that the specific surface areas of two ACs obtained from pistachio nut shells activated with KOH and treated in two different thermal configurations (a conventional electric oven and a modified microwave oven), were very similar (700 and 796 m2 g-1), thus suggesting that the two methods (conventional and non-conventional) are effective for the preparation of ACs.

Figure 4. Specific surface area of activated carbons obtained by chemical activation of lignocellulosic materials with KOH, NaOH and K2CO3

26 Characterization Techniques and Applications in the Wastewater Treatment

In general, the preparation of ACs by chemical activation with KOH and NaOH allows to obtain carbons with high specific surface areas (>1000 m2 g-1). However, KOH and NaOH are corrosive and deleterious chemicals (Hayashi et al., 2002a). For this reason, recent studies have proposed the preparation of activated carbons by chemical activation with K2CO3 in one step, in which the lignocellulosic materials is impregnated with a K2CO3 solution and finally the impregnated precursor is thermally treated. K2CO3 is a not

Table 3 summarizes the experimental conditions used in the preparation of ACs from lignocellulosic materials by chemical activation with NaOH, KOH and K2CO3. Carbons obtained by activation with NaOH are the materials showing higher SBET (see Figure 4), for example, the carbon obtained from flamboyant exhibiting a SBET near to 2500 m2 g-1. Also, the activation with K2CO3 renders carbons with a competitive SBET (between 1200 and 1800

Other interesting observation is that the specific surface areas of two ACs obtained from pistachio nut shells activated with KOH and treated in two different thermal configurations (a conventional electric oven and a modified microwave oven), were very similar (700 and 796 m2 g-1), thus suggesting that the two methods (conventional and non-conventional) are

Figure 4. Specific surface area of activated carbons obtained by chemical activation of

Flamboyant

Plum kernels

Jatropha curcas

Pistachio shell

Cork waste

Soybean oil cake

Palm shell

Chickpea husk

Waste apricot

 K2 CO3

NaOH

lignocellulosic materials with KOH, NaOH and K2CO3

deleterious reagent and it is broadly used for food additives (Hayashi et al., 2002a).

m2 g-1) compared with those obtained by activation with KOH or NaOH.

KOH

effective for the preparation of ACs.

Olive-mill waste water

Soybean oil cake

0

500

1000

1500

Specific surface (m2 g-1

)

2000

2500

3000

Cassava peel

Stem of

endocarp

date palm

Corn cobs

\*

Pistachio nut shell

Pistachio nut shell\*

Coffee


#### **2.2 Physical or thermal activation**

In a physical activation process, the lignocellulosic precursor is carbonized under an inert atmosphere, and the resulting carbon is subjected to a partial and controlled gasification at high temperature with steam, carbon dioxide, air or a mixture of these (Rodriguez-Reinoso & Molina-Sabio, 1992). Steam and CO2 are the two activating gases more used in the physical activation of carbons. According to the literature, steam or CO2 react with the carbon structures to produce CO, CO2, H2 or CH4. The degree of activation is normally referred to as "burn-off" and it is defined as the weight difference between the carbon and the activated carbon divided by the weight of the original carbon on dry basis according with the following equation,

$$Burn\,off = \frac{W\_0 - W\_1}{W\_0} X100\% \tag{1}$$

Precursor Carbonization Conditions Activation conditions Reference

Atm. Temperature

Heating rate

Atm. Flow

(cm3 min-1)

(ºC min-1)

N2 800 10 CO2 85 Mourão et al. (2011)

N2 800 10 CO2 85 Nabais et al. (2011)

N2 950 - CO2 250 Phan et al. (20069

N2 800 5 CO2 85 Nabais et al. (2008)

N2 800 20 CO2 200 Aworn et al. (2008)

N2 800 10 CO2 150 Rodriguez-Mirasol et

N2 950 - CO2 250 Phan et al. (2006)

N2 800 20 CO2 200 Aworn et al. (2008)

N2 900 10 CO2 - Lua et al. (2006)

350 - Air 850 - CO2 300 Moreno-Castilla et al.

N2 900 10 CO2 100 Lua et al. (2004)

N2 800 10 CO2 100 Yang & Lua (2003)

(2001)

al. (19939

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 29

200 Aworn et al. (2008)

(ºC)

Temperature

Heating rate

(ºC min-1 )

(ºC)

Almond shell 400 10

Almond shell 400 10

Bagasse bottom

500 20

N2

800 20 CO2

ash

Coconut Fibers 950 -

Coffee

700 5

endocarp

Corncob 500 20

Eucalyptus

350 10

kraft lignin

Jute 950 -

500 500 500 500

Macadamia

500 20

nut-shell

Oil-palm-shell 600 10

Olive-mill

waste

Pistachio-nut

500 10

shells

Pistachio-nut

500 10

shells

Sawdust fly ash 500 20

Vine shoots 400 10

N2

800 20 CO2

N2 800 10 CO2 85 Mourão et al. (2011)

Table 4. Experimental conditions of activated carbons obtained from different lignocellulosic precursors by physical activation with CO2

200 Aworn et al. (2008)

where W0 is the weight of the original carbon and W1 refers to the mass of the activated carbon. The use of CO2 during the activation process of a carbon material develops narrow micropores, while steam widens the initial micropores of the carbon. At high degrees of burn-off, steam generates activated carbons with larger meso and macropore volumes than those prepared by CO2. Consequently, CO2 creates activated carbons with larger micropore volumes and narrower micropore size distributions than those activated by steam (Mohamed et al., 2010) micropores,

Tables 4 and 5 show the experimental conditions used in the preparation of activated carbons from lignocellulosic materials by physical activation with CO2, steam and steam-N2 admixtures. Normally, in these experiments the lignocellulosic precursor is carbonized in an inert atmosphere (N2) at temperatures ranging from 400 to 950 ºC to produce carbons with rudimentary pore structures. These carbons are then activated with the selected gasification agent at temperatures around 800-1000 ºC to produce the final activated carbons.

Some additional studies combine the thermal or physical activation with chemical activation (also known as physicochemical activation, Table 6). Normally, physicochemical activation is performed by changing the activation atmosphere of the chemical activation by a gasification atmosphere (i.e., steam) at higher temperatures. In other cases, the chemical activation is carried out directly under the presence of a gasifying agent. The combination of both types of carbon activation renders ACs with textural and chemical properties which are different from those obtained by any of the activations alone. For example, steam reduces the occurrence of heteroatoms into the carbon structures. Also, combination of oxidizing reagents in the liquid phase (i.e., nitric or sulfuric acids) with gasification agents improves the development of porosity on the final carbons.

Figure 5 shows the specific surface area of activated carbons obtained by physical and physiochemical activation according with the experimental conditions cited in Tables 4, 5 and 6. In general, the ACs obtained by physical activation with CO2 show a higher specific surface area that those obtained by activation with steam. Additionally, the ACs obtained by physical activation with CO2 using high heating rates (20 ºC min-1) are the adsorbents showing lower SBET (Corncob, Bagasse bottom ash and Sawdust fly ash).


ܺͳͲͲΨ (1)

28 Characterization Techniques and Applications in the Wastewater Treatment

In a physical activation process, the lignocellulosic precursor is carbonized under an inert atmosphere, and the resulting carbon is subjected to a partial and controlled gasification at high temperature with steam, carbon dioxide, air or a mixture of these (Rodriguez-Reinoso & Molina-Sabio, 1992). Steam and CO2 are the two activating gases more used in the physical activation of carbons. According to the literature, steam or CO2 react with the carbon structures to produce CO, CO2, H2 or CH4. The degree of activation is normally referred to as "burn-off" and it is defined as the weight difference between the carbon and the activated carbon divided by the weight of the original carbon on dry basis according

ݎݑܤ݂݂݊ ൌ ௐబିௐభ

ௐబ

a

where W0 is the weight of the original carbon and W1 refers to the mass of the activated carbon. The use of CO2 during the activation process of a carbon material develops narrow micropores, while steam widens the initial micropores of the carbon. At high degrees of burn-off, steam generates activated carbons with larger meso and macropore volumes than those prepared by CO2. Consequently, CO2 creates activated carbons with larger micropore volumes and narrower micropore size distributions than those activated by steam

Tables 4 and 5 show the experimental conditions used in the preparation of activated carbons from lignocellulosic materials by physical activation with CO2, steam and steam-N2 admixtures. Normally, in these experiments the lignocellulosic precursor is carbonized in an inert atmosphere (N2) at temperatures ranging from 400 to 950 ºC to produce carbons with rudimentary pore structures. These carbons are then activated with the selected gasification

Some additional studies combine the thermal or physical activation with chemical activation (also known as physicochemical activation, Table 6). Normally, physicochemical activation is performed by changing the activation atmosphere of the chemical activation by a gasification atmosphere (i.e., steam) at higher temperatures. In other cases, the chemical activation is carried out directly under the presence of a gasifying agent. The combination of both types of carbon activation renders ACs with textural and chemical properties which are different from those obtained by any of the activations alone. For example, steam reduces the occurrence of heteroatoms into the carbon structures. Also, combination of oxidizing reagents in the liquid phase (i.e., nitric or sulfuric acids) with gasification agents improves

Figure 5 shows the specific surface area of activated carbons obtained by physical and physiochemical activation according with the experimental conditions cited in Tables 4, 5 and 6. In general, the ACs obtained by physical activation with CO2 show a higher specific surface area that those obtained by activation with steam. Additionally, the ACs obtained by physical activation with CO2 using high heating rates (20 ºC min-1) are the adsorbents

showing lower SBET (Corncob, Bagasse bottom ash and Sawdust fly ash).

agent at temperatures around 800-1000 ºC to produce the final activated carbons.

the development of porosity on the final carbons.

**2.2 Physical or thermal activation** 

with the following equation,

(Mohamed et al., 2010)


Table 6. Experimental conditions of activated carbons obtained from different lignocellulosic precursors by physiochemical activation

Figure 5. Specific surface of activated carbons obtained by physical activation with CO2 and

The advantages and drawbacks of the different types of carbon activation are discussed in

water vapor and by physiochemical activation

Eucalyptus kraft lignin

Olive-mill waste

Pistachio-nut shells

Coffee endocarp

CO2

Pistachio-nut shells

Macadamia

Oil-palm-shell

nut-shell

Bagasse bottom ash

Corncob

Sawdust fly ash

Almond tree

Water vapor

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 31

Walnut shell

Almond shell Olive stone

pruning

Date stones

Olive stones

Sugarcane bagasse

Physiochemical

Date stones

 Date stones

M. oleiferu seed

M.

Activated carbons are obtained in one step

Better control of textural properties

 High surface area of the ACs Well-developed microporosity Narrow micropore size distributions Reduction of the mineral matter content

Lower temperatures of pyrolysis (600 an 800 ºC)

the following points.

Almond shell

0

500

1000

Specific surface (m2 g-1

)

1500

2000

shoots.

Vine

Almond shell Jute Coconut Fibers

**3.1 Chemical method** 

Shorter activation times

Advantages

High yield

**3. Analysis of the methods used in the preparation of ACs** 

Figure 5. Specific surface of activated carbons obtained by physical activation with CO2 and water vapor and by physiochemical activation

#### **3. Analysis of the methods used in the preparation of ACs**

The advantages and drawbacks of the different types of carbon activation are discussed in the following points.

#### **3.1 Chemical method**

Advantages

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

(2009)

(2009)

(2009)

30 Characterization Techniques and Applications in the Wastewater Treatment

(2009)

Precursor Carbonization Conditions Activation conditions Reference Temperature (ºC) Heating rate (ºC min-1 ) Atm. Temperature

(ºC) Heating rate (ºC min-1) Atm. Flow (cm3 min-1) Almond shell 600 -

Almond tree

600 -

pruning

Date stones 700 10

M. oleiferu

seed

Olive stone 600 -

stone

Walnut shell 600 -

Precursor Activating

Temperature

Heating rate

Atm. Flow (cm3 min-1) Reference

(ºC min-1)

H3PO4 600 - Steam - Hazourli et al.

Date stones HNO3 600 - Steam - Hazourli et al.

Olive stones CaCl2 800 - CO2 100 Juárez-Galán et al.

H2SO4 160 10 Air 2000 Valix et al. (2004)

Table 6. Experimental conditions of activated carbons obtained from different lignocellulosic precursors by physiochemical activation

Sugarcane bagasse

agent

Date stones

(ºC)

N2 850 - Steam -N2

N2 850 - Steam -N2

N2 700 10 Steam 100 Bouchelta et al.


N2 850 - Steam -N2

N2 850 - Steam -N2 150 González et al.

Table 5. Experimental conditions of activated carbons obtained from various lignocellulosic precursors by physical activation with steam

150 González et al.

(2009)

150 González et al.

(2009)

(2008)

(1997)

150 González et al.

(2009)


**6. References** 

0165-2370.

691), ISSN 0008-6223.

(999-1007), ISSN 0008-6223.

pp. (185-193), ISSN 0165-2370.

[1] Adinata, D., Wan-Daud, W.M. & Kheireddine-Aroua, M. (2007). Preparation and characterization of activated carbon from palm shell by chemical activation with K2CO3. *Bioresource Technology,* Vol. 98, No. 1, (January 2007), pp. (145–149), ISSN 0960-8524. [2] Ahmedna, M., Marshall, W.E. & Rao, R.M. (2000). Production of granular activated carbons from select agricultural by-products and evaluation of their physical, chemical and adsorption properties. *Bioresource Technology,* Vol. 71, No. 2, (January 2000), pp. (113-1239, ISSN 0960-8524. Arami-Niya, A., Daud, W.M.A.W. & Mjalli, F.S. (2010). Using granular activated carbon prepared from oil palm shell by ZnCl2 and physical activation for methane adsorption. *Journal of Analytical and Applied Pyrolysis,* Vol. 89, No.

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 33

[3] Arami-Niya, A., Daud, W.M.A.W. & Mjalli, F.S. (2011). Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption. *Chemical Engineering Research and Design,* 

[4] Aravindhan, R., Raghava-Rao, J. & Unni-Nair, B. (2009). Preparation and characterization of activated carbon from marine macro-algal biomass. *Journal of Hazardous Materials,* Vol. 162, No. 2-3, (March 2009), pp. (688–694), ISSN 0304-3894. [5] Aworn, A., Thiravetyan, P. & Nakbanpote, W. (2008). Preparation and characteristics of agricultural waste activated carbon by physical activation having micro and mesopores. *Journal of Analytical and Applied Pyrolysis,* Vol. 82, No. 2, (July 2008), pp. (279–285), ISSN

[6] Azevedo, D.C.S., Araújo, J.C.S., Bastos-Neto, M., Torres, A.E.B., Jaguaribe, E.E. & Cavalcante C.L. (2007). Microporous activated carbon prepared from coconut shells using chemical activation with zinc chloride. *Microporous and Mesoporous Materials,* Vol.

[7] Bagheri, N. & Abedi, J. (2009). Preparation of high surface area activated carbon from corn by chemical activation using potassium hydroxide. *Chemical Engineering Research* 

[8] Boudrahem, F., Aissani-Benissad, F. & Aït-Amar, H. (2009). Batch sorption dynamics and equilibrium for the removal of lead ions from aqueous phase using activated carbon developed from coffee residue activated with zinc chloride. *Journal of Environmental Management,* Vol. 90, No. 10, (July 2009), pp. (3031–3039), ISSN 0301-4797. [9] Carvalho, A., Gomes, M., Mestre, A.S., Pires, J. & Brotas de Carvalho, M. (2004). Activated carbons from cork waste by chemical activation with K2CO3. Application to adsorption of natural gas components. *Carbon,* Vol. 42, No. 3, (January 2004), pp. (667–

[10] Caturla, F., Molina-Sabio, M., & Rodríguez-Reynoso, F. (1991). Preparation of activated carbon by Chemical activation with ZnCl2. *Carbon,* Vol. 29, No. 7, (February 1991), pp.

[11] Elizalde-González, M.P., Mattusch, J., Peláez-Cid, A.A. & Wennrich, R. (2007). Characterization of adsorbent materials preparaed from avocado kernel sedes: Natural, activated and carbonized forms. *Journal of Analytical and Applied Pyrolysis,* Vol. 78, No. 1,

*and Design,* Vol. 87, No. 8, (August 2009), pp. (1059–1064), ISSN 0263-8762.

2, (November 2010), pp. (197-203), ISSN 0165-2370.

Vol. 89, No. 6, (June 2011), pp. (657–664), ISSN 0263-8762.

100, No. 1-3, (March 2007), pp. (361-364), ISSN 1387-1811.

Disadvantages


#### **3.2 Physical method**

Advantages


#### Disadvantages


### **4. Conclusions**

Attending to the works considered in this chapter, chemical activation is the most used method for the preparation of ACs (~60 %) from lignocellulosic precursors. Physical activation methods is used in 28% of the studies and a low quantity of studies combine both methods (i.e., physicochemical) to produce ACs. H3PO4 and ZnCl2 are the two more employed activating agents in the impregnation of lignocellulosic materials (30% and 24 %, respectively), whereas alkaline reagents such as KOH, NaOH and K2CO3 have been considered because ACs with high specific surface can be obtained (1500-2500 m2 g-1). Physical activation of lignocellulosic precursors normally renders carbons with lower specific surface area. However, when compared with chemical activation, this method is not corrosive and does not require a washing step.

#### **5. Acknowledgments**

The author thanks the support of CONACYT (AGS-2010-C02-143917), DGEST (4220.11-P), Instituto Tecnológico de Aguascalientes (México) and Instituto Nacional del Carbón (Oviedo, España).

#### **6. References**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

32 Characterization Techniques and Applications in the Wastewater Treatment

Avoids the incorporation of impurities coming from the activating agent

Attending to the works considered in this chapter, chemical activation is the most used method for the preparation of ACs (~60 %) from lignocellulosic precursors. Physical activation methods is used in 28% of the studies and a low quantity of studies combine both methods (i.e., physicochemical) to produce ACs. H3PO4 and ZnCl2 are the two more employed activating agents in the impregnation of lignocellulosic materials (30% and 24 %, respectively), whereas alkaline reagents such as KOH, NaOH and K2CO3 have been considered because ACs with high specific surface can be obtained (1500-2500 m2 g-1). Physical activation of lignocellulosic precursors normally renders carbons with lower specific surface area. However, when compared with chemical activation, this method is not

The author thanks the support of CONACYT (AGS-2010-C02-143917), DGEST (4220.11-P), Instituto Tecnológico de Aguascalientes (México) and Instituto Nacional del Carbón

Disadvantages

**3.2 Physical method** 

Advantages

Cheaper

Disadvantages

**4. Conclusions** 

**5. Acknowledgments** 

(Oviedo, España).

 Corrosiveness of the process Requires a washing stage Inorganic impurities More expensive

 The process is not corrosive A washing stage is not required

Poorer control of the porosity

 The activated carbons are obtained in two steps Higher temperatures of activation (800-1000 ºC)

corrosive and does not require a washing step.


[25] Mohamed, A. R., Mohammadi, M. & Darzi, G.N. (2010). Preparation of carbon molecular sieve from lignocellulosic biomass: A review. *Renewable and Sustainable* 

Thermal Treatments and Activation Procedures Used in the Preparation of Activated Carbons 35

*Energy Reviews,* Vol. 14, No. 6, (August 2010), pp. (1591-1599), ISSN 1364-0321. [26] Mohammadi, S.Z., Karimi, M.A., Afzali, D. & Mansouri, F. (2010). Removal of Pb(II) from aqueous solutions using activated carbon from Sea-buckthorn stones by chemical activation. *Desalination,* Vol. 262, No. 1-3, (November 2010), pp. (86–93), ISSN 0011-9164. [27] Moreno-Castilla, C., Carrasco-Marín, F., López-Ramón, M.V. & Alvarez-Merino, M.A. (2001). Chemical and physical activation of olive-mill waste water to produce activated

carbons. *Carbon,* Vol. 39, No. 9, (August 2001), pp. (1415–1420), ISSN 0008-6223. [28] Mourão, P.A.M., Laginhas, C., Custódio, F., Nabais, J.M.V., Carrott, M.M.L. & Ribeiro-Carrot, M.M.L. (2011). Influence of oxidation process on the adsorption capacity of activated carbons from lignocellulosic precursors. *Fuel Processing Technology,* Vol. 92,

[29] Nabais, J.V., Carrott, P., Ribeiro-Carrott, M.M.L., Luz, V. & Ortiz, A.L. (2008). Influence of preparation conditions in the textural and chemical properties of activated carbons from a novel biomass precursor: The coffee endocarp. *Bioresource Technology,* Vol. 99,

[30] Namasivayam, C. & Kadirvelu, K. (1997). Activated carbons prepared from coir pith by Physical and Chemical activation methods. *Bioresource Technology,* Vol. 62, No. 3,

[31] Olivares-Marín, M., Fernández-González, C., Macías-García, A. & Gómez-Serrano, V. (2006). Preparation of activated carbon from cherry stones by chemical activation with ZnCl2. *Applied Surface Science,* Vol. 252, No. 17, (June 2006), pp. (5967–5971), ISSN 0169-

[32] Phan, N.H., Rio, S., Faur, C., Le Coq, L., Le Cloirec, P. & Nguyen, T.H. (2006). Production of fibrous activated carbons from natural cellulose (jute, coconut) fibers for water treatment applications. *Carbon,* Vol. 44, No. 12, (October 2006), pp. (2569–2577,

[33] Prahas, D., Kartika, Y., Indraswati, N. & Ismadji, S. (2008). Activated carbon from jackfruit peel waste by H3PO4 chemical activation: Pore structure and surface chemistry characterization. *Chemical Engineering Journal,* Vol. 140, No. 1-3, (July 2008), pp. (32-42),

[34] Puziy, A.M., Poddubnaya, O.I., Martínez-Alonso, A., Suárez-García, F. & Tascón, J. (2005). Surface chemistry of phosphorus-containing carbons of lignocellulosic origin.

[35] Rodriguez-Mirasol, J., Cordero, T. & Rodríguez, J.J. (1993). Preparation and characterization of activated Carbons from eucalyptus krafl- lignin. *Carbon,* Vol. 31, No.

**[36]** Rodríguez-Reinoso, F. & Molina-Sabio, M. (1992). Activated carbons from lignocellulosic materials by chemical and/or physical activation: an overview. *Carbon,* 

[37] Sudaryanto, Y., Hartono, S.B., Irawaty, W., Hindarso, H. & Ismadji, S. (2006). High surface area activated carbon prepared from cassava peel by chemical activation. *Bioresource Technology,* Vol. 97, No. 5, (March 2006), pp. (734–739), ISSN 0960-8524.

*Carbon,* Vol. 43, No. 14, (November 2005), pp. (2857-2868), ISSN 0008-6223.

No. 2, (February 2011), pp. ( 241-246), ISSN 0378-3820.

No. 15, (October 2008), pp. (7224–7231), ISSN 0960-8524.

(December 1997), pp. (123-127), ISSN 0960-8524.

1, (May 1992), pp. (87-95), ISSN 0008-6223.

Vol. 30, No. 7, (1992), pp. (1111-1118), ISSN 0008-6223

4332.

ISSN 0008-6223).

ISSN 1385-8947.


34 Characterization Techniques and Applications in the Wastewater Treatment

[12] Erdoğan, S., Önal, Y., Akmil-Başar, C., Bilmez-Erdemoğlu, S., Sarc-Özdemir, Ç., Köseoğlu, E. & İçduygu, G. (2005). Optimization of nickel adsorption from aqueous solution by using activated carbon prepared from waste apricot by chemical activation. *Applied Surface Science,* Vol. 252, No. 5, (December 2005), pp. (1324–1331), ISSN 0169-

[13] Foo, K.Y. & Hameed, B.H. (2011). Preparation and characterization of activated carbon from pistachio nut shells via microwave-induced chemical activation. *Biomass and* 

[14] González, J.F., Román, S., Encinar, J.M. & Martínez, G. (2009). Pyrolysis of various biomass residues and char utilization for the production of activated carbons. *Journal of Analytical and Applied Pyrolysis,* Vol. 85, No. 1-2, (MAy 2009), pp. (134–141), ISSN 0165-

[15] Hared, I.A., Dirion, J.L., Salvador, S., Lacroix, M. & Rio, S. (2007). Pyrolysis of wood impregnated with phosphoric acid for the production of activated carbon: Kinetics and porosity development studies. *Journal of Analytical and Applied Pyrolysis,* Vol. 79, No. 1-2,

[16] Hayashi, J., Horikawa, T., Takeda, I., Muroyama, K. & Ani, F.N. (2002a). Preparing activated carbon from various nutshells by chemical activation with K2CO3. *Carbon,* Vol.

[17] Hayashi, J., Horikawa, T., Takeda, I., Muroyama, K. & Ani, F.N. (2002b). Activated carbon from chickpea husk by chemical activation with K2CO3: preparation and characterization. *Microporous and Mesoporous Materials,* Vol. 55, No. 1, (August 2002), pp.

[18] Hazourli S., Ziati M. & Hazourli A. (2009). Characterization of activated carbon prepared from lignocellulosic natural residue:-Example of date stones-. *Physics Procedia,* 

[19] Hu, Z., Srinivasan, M.P. & Ni, Y. (2001). Novel activation process for preparing highly microporous and mesoporous activated carbons. *Carbon,* Vol. 39, No. 6, (May 2001), pp.

[20] Jibril, B., Houache, O., Al-Maamari, R. & Al-Rashidi, B. (2008). Effects of H3PO4 and KOH in carbonization of lignocellulosic material. *Journal of Analytical and Applied* 

[21] Juárez-Galán, J., Silvestre-Albero, A., Silvestre-Albero, J. & Rodríguez-Reinoso, F. (2009). Synthesis of activated carbon with highly developed ''mesoporosity". *Microporous and Mesoporous Materials,* Vol. 117, No. 1-2, (January 2009) pp. 519-521, ISSN

[22] Kaghazchi, T., Asasian-Kolur, N. & Soleimani, M. (2010). Licorice residue and Pistachionut shell mixture: A promising precursor for activated carbon. *Journal of Industrial and* 

[24] Lua, A.C., Lau, F.Y. & Guo, J. (2006). Influence of pyrolysis conditions on pore development of oil-palm-shell activated carbons. *Journal of Analytical and Applied* 

*Pyrolysis,* Vol. 76, No. 1-2, (June 2006), pp. (96–102), ISSN 0165-2370.

*Engineering Chemistry,* Vol. 16, No. 3, (May 2010), pp. (368–374), ISSN 1226-086X. [23] Lua, A.C. & Yang, T. (2004). Effect of activation temperature on the textural and chemical properties of potassium hydroxide activated carbon prepared from pistachionut shell. *Journal of Colloid and Interface Science,* Vol. 274, No. 2, (June 2004), pp. (594–

*Pyrolysis,* Vol. 83, No. 2, (November 2008), pp. (151-156), ISSN 0165-2370.

*Energy,* Vol. 35, No. 7, (July 2011), pp. (3257-3261), ISSN 0961-9534.

(May 2007), pp. (101–105), ISSN 0165-2370.

(63-68), ISSN 1387-1811.

(877-886), ISSN 0008-6223.

1387-1811.

601), ISSN 0021-9797.

40, No. 13, (April 2002), pp. (2381–2386), ISSN 0008-6223.

Vol. 2, No. 3, (November 2009), pp. 1039-1043, ISSN 1875-3892.

4332.

2370.


**3** 

*Spain* 

Carlos J. Durán-Valle *Universidad de Extremadura* 

**Techniques Employed in the Physicochemical** 

Activated carbons have been widely used as adsorbents, catalyst supports, catalysts, and electronic materials due to its properties: high surface area, large pore volume, and

Porous solids are materials full of pores; when the main type of pore is microporous, these materials have large internal surfaces. This property is of great importance in adsorption, and its study is essential in the characterization of activated carbons. Pore structure and specific surface can be controlled by several factors: carbonization atmosphere, activation agent, precursor, time and temperature of thermal treatment, the use of templates to synthesize the precursor, particle size, and chemical treatment. The same factors, but with different intensity, control the functional groups in the surface. Also, the functional groups in activated carbons were found to be responsible for the variety in physical and chemical properties (Bandosz, 2009). So, a great amount research has focused on how to modify and characterize the surface functional groups of activated carbons in order to improve their applications or understand their properties (Calvino-Casilda et al., 2010; Moreno-Castilla, 2004; Shen et al., 2008). In the last decades, a large number of techniques have been developed to study various surface properties in solids (Somorjai, 1994). The frontiers of instrumentation are constantly being pushed toward better conditions: finer detail (spatial resolution, energy resolution, and composition accuracy), better sensibility, automation, and cheaper equipment. Activated carbon presents some peculiarities: it is a non-crystalline material (amorphous), is a non-stoichiometric solid with variable composition, and it is opaque to most wavelengths and species used in a characterization laboratory. The chemistry of carbon is extremely complex (Schlogl, 1997; Do, 1998); the main reason for this complexity lies in the pronounced tendency of this element to form homonuclear bonds in three bonding geometries (*sp*, *sp2*, and *sp3*) and in the moderate electronegativity of carbon, which allows strong covalent interactions with other elements. Because of the use of only one technique does not provide all the necessary information about surfaces, the tendency is to use a combination of techniques. In this chapter, some of the more common techniques

chemical-modifiable surface (Do, 1998). These properties determine its application.

used in the characterization of activated carbons are shown.

**1. Introduction** 

**Characterization of Activated Carbons** 


## **Techniques Employed in the Physicochemical Characterization of Activated Carbons**

Carlos J. Durán-Valle *Universidad de Extremadura Spain* 

#### **1. Introduction**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

36 Characterization Techniques and Applications in the Wastewater Treatment

[38] Tay, T., Ucar, S. & Karagöz, S. (2009). Preparation and characterization of activated carbon from waste biomass. *Journal of Hazardous Materials,* Vol. 165, No. 1-3, (June 2009),

[39] Tongpoothorn, W., Sriuttha, M., Homchan, P., Chanthai, S. & Ruangviriyachai, C. (2011). Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties *Chemical Engineering Research and Design,* Vol. 89, No. 3, (March 2011), pp.

[40] Torregrosa, R. & Martín-Martínez, J.M. (1991). Activation of lignocellulosic materials: a comparison between chemoical, physical and combined activation in terms of porous

[42] Valix, M., Cheung, W.H. & McKay, G. (2004). Preparation of activated carbon using low temperature carbonisation and physical activation of high ash raw bagasse for acid dye adsorption. *Chemosphere,* Vol. 56, No. 5, (August 2004) pp. (493–501), ISSN 0045-6535. [43] Vargas, J.E., Gutierrez, L.G. & Moreno-Piraján, J.C. (2010). Preparation of activated carbons from seeds of Mucuna mutisiana by physical activation with steam. *Journal of Analytical and Applied Pyrolysis,* Vol. 89, No. 2, (April 2001), pp. (307–312), ISSN 0165-

[44] Vargas, A.M.M., Cazetta, A.L., Garcia, C.A., Moraes, J.C.G., Nogami, E.M., Lenzi, E., Costa W.F. & Almeida, V.C. (2011). Preparation and characterization of activated carbon from a new raw lignocellulosic material: Flamboyant (Delonix regia) pods. *Journal of Environmental Management,* Vol. 92, No. 1, (January 2011), pp. (178-184), ISSN

[45] Warhurst, A.M., Fowler, G.D., McConnachie, G.L. & Pollard, S.J.T. (1997). Pore structure and adsorption characteristics of steam pyrolysis carbons from Moringa Oleifera. *Carbon,* Vol. 35, No. 8, (February 1997), pp. (1039-1045), ISSN 0008-6223. [46] Yagmur, E., Ozmak, M. & Aktas, Z. (2008). A novel method for production of activated carbon from waste tea by chemical activation with microwave energy. *Fuel,* Vol. 87, No.

[47] Yang, J. & Qiu, K. (2010). Preparation of activated carbons from walnut shells via vacuum chemical activation and their application for methylene blue removal. *Chemical Engineering Journal,* Vol. 165, No. 1, (November 2010), pp. (209-217), ISSN 1385-8947. [48] Yavuz, R., Akyildiz, H., Karatepe N. & Çetinkaya, E. (2010). Influence of preparation conditions on porous structures of olive stone activated by H3PO4. *Fuel Processing* 

[49] Zuo, S., Yang, J., Liu, J. & Cai, X. (2009). Significance of the carbonization of volatile pyrolytic products on the properties of activated carbons from phosphoric acid activation of lignocellulosic material. *Fuel Processing Technology,* Vol. 90, No. 7-8, (July-

texture. *Fuel*, Vol. 70, No. 10, (October 1991), pp. (1173-1180), ISSN 0016-2361. [41] Tseng, R. (2007). Physical and chemical properties and adsorption type of activated carbon prepared from plum kernels by NaOH activation. *Journal of Hazardous Materials,* 

Vol. 147, No. 3, (August 2007), pp. (1020–1027), ISSN 0304-3894.

15-16, (November 2008), pp. (3278–3285), ISSN 0016-2361.

August 2009), pp. (994-1001), ISSN 0378-3820.

*Technology,* Vol. 91, No. 1, (January 2010), pp. (80-87), ISSN 0378-3820.

pp. (481–485), ISSN 0304-3894.

(335–340), ISSN 0263-8762.

2370.

0301-4797.

Activated carbons have been widely used as adsorbents, catalyst supports, catalysts, and electronic materials due to its properties: high surface area, large pore volume, and chemical-modifiable surface (Do, 1998). These properties determine its application.

Porous solids are materials full of pores; when the main type of pore is microporous, these materials have large internal surfaces. This property is of great importance in adsorption, and its study is essential in the characterization of activated carbons. Pore structure and specific surface can be controlled by several factors: carbonization atmosphere, activation agent, precursor, time and temperature of thermal treatment, the use of templates to synthesize the precursor, particle size, and chemical treatment. The same factors, but with different intensity, control the functional groups in the surface. Also, the functional groups in activated carbons were found to be responsible for the variety in physical and chemical properties (Bandosz, 2009). So, a great amount research has focused on how to modify and characterize the surface functional groups of activated carbons in order to improve their applications or understand their properties (Calvino-Casilda et al., 2010; Moreno-Castilla, 2004; Shen et al., 2008). In the last decades, a large number of techniques have been developed to study various surface properties in solids (Somorjai, 1994). The frontiers of instrumentation are constantly being pushed toward better conditions: finer detail (spatial resolution, energy resolution, and composition accuracy), better sensibility, automation, and cheaper equipment. Activated carbon presents some peculiarities: it is a non-crystalline material (amorphous), is a non-stoichiometric solid with variable composition, and it is opaque to most wavelengths and species used in a characterization laboratory. The chemistry of carbon is extremely complex (Schlogl, 1997; Do, 1998); the main reason for this complexity lies in the pronounced tendency of this element to form homonuclear bonds in three bonding geometries (*sp*, *sp2*, and *sp3*) and in the moderate electronegativity of carbon, which allows strong covalent interactions with other elements. Because of the use of only one technique does not provide all the necessary information about surfaces, the tendency is to use a combination of techniques. In this chapter, some of the more common techniques used in the characterization of activated carbons are shown. resolution, and with

range of 0.1 to 0.4 cm3 g-1, and the surface area is in the range of 10-100 m2 g-1. Their contribution to adsorption is significant, and they act as transport to micropores. Micropores have a similar volume, but the surface area is the most important, sometimes near to 1000

Techniques Employed in the Physicochemical Characterization of Activated Carbons 39

Type Width (nm)

Mesopores >2 and < 50

The characterization of porous activated carbon and its derivatives has been a subject of great interest for many decades. Two main experimental tools are used for this study:

Micropores Mesopores Macropores many for

Mercury porosimetry is a technique that was originally developed to determine pore sizes in the macropore range, where the gas adsorption is not adequate (Gregg & Sing, 1982). Since the contact angle of mercury with solids is >90º, an excess pressure *p* is required to force the liquid mercury into a pore of radius *r*. Washburn (1921) suggested the following basic

*p*

The technique of mercury porosimetry consists of measuring the extent of mercury penetration into the pores of a solid as a function of the applied pressure. Automatic porosimeters are now in use for the routine examination of pore structures for catalysts, adsorbents, cements, refractory materials, and other materials. The measure range of porosimeters application extends from macropores to near of the limit between micropores and mesopores. Thus, there is an overlap with the gas adsorption method in the mesopore

The ability to adsorb and desorb gases from the coals has been known for a long time (Scheele, 1780). A large amount of the information about the physical structure of a surface (i.e., specific surface and pores) comes from the amount of gas adsorbed on this surface as a function of gas pressure at a given temperature. Mercury porosimetry and gas adsorption are complementary techniques: porosimetry can measure mesopores and macropores, and

The curves derived from these experiments are called **adsorption isotherms**. They can be used to determine thermodynamic parameters (e.g., heat of adsorption), the pore distribution, and

(2)

is the contact angle (141º)

*r* 2 cos

is the surface tension of mercury (484 mN m-1) and

Micropores < 2

Macropores > 50

Table 1. IUPAC classification of pores according to their width.

mercury porosimetry and gas adsorption.

recommended by IUPAC (Sing et al, 1985).

gas adsorption measures micropores and mesopores.

m2 g-1.

equation:

where 

range.

**4. Gas adsorption** 

#### **2. Density measurements and pore volume**

There are several "densities" related with activated carbons. These can be mentioned as:




The total volume of pores can be calculated from Hg and He densities by:

$$V = \frac{1}{\rho\_{\text{He}}} - \frac{1}{\rho\_{\text{Hg}}} \tag{1}$$

 where *V* is the pore volume, *He* is the He density, and *Hg* is Hg density, respectively.

In preparation of charcoal, these values have been studied for different temperatures and times of preparation of charcoal (Durán-Valle et al., 2006; Pastor-Villegas & Durán-Valle, 2002).

#### **3. Porosimetry**

The pores of solids are of different kinds. The individual pores may vary in size and in shape. With respect to the shape, in activated carbons, the predominant type is the slit-shape pore. But, the width of the pores is also of special interest for many purposes. A classification of pores according to their average width, which was adopted by the IUPAC (IUPAC, 1972; Sing et al., 1985) is shown in Table 1.

In recent years, the micropore range has been subdivided into very narrow pores (until 0.8 nm) or **ultramicropores**, where the enhancement of interaction potential is caused by the similarity in size between the pore and molecules, and **supermicropores**, which have a width (0.8 to 2.0 nm) between ultramicropores and mesopores (Gregg & Sing, 1982). Carbon-based materials usually have a bimodal pore size distribution, with one dominant peak being less than approximately 2 nm and the other major peak usually greater than 50 nm (Do et al., 2008).

The volume of macropores it is usually on the order of 0.2-0.5 cm3 g-1, but the associated area is very small, on the order of 0.5 m2 g-1, which is negligible in an activated carbon (Do, 1998). Macropores are not important for the adsorption capacity, but their importance is because they act as transport pores to the meso- and micropores. Mesopores have a volume in the range of 0.1 to 0.4 cm3 g-1, and the surface area is in the range of 10-100 m2 g-1. Their contribution to adsorption is significant, and they act as transport to micropores. Micropores have a similar volume, but the surface area is the most important, sometimes near to 1000 m2 g-1.


Table 1. IUPAC classification of pores according to their width.

The characterization of porous activated carbon and its derivatives has been a subject of great interest for many decades. Two main experimental tools are used for this study: mercury porosimetry and gas adsorption.

Mercury porosimetry is a technique that was originally developed to determine pore sizes in the macropore range, where the gas adsorption is not adequate (Gregg & Sing, 1982). Since the contact angle of mercury with solids is >90º, an excess pressure *p* is required to force the liquid mercury into a pore of radius *r*. Washburn (1921) suggested the following basic equation: range,

$$r = \frac{2\gamma\cos\theta}{p} \tag{2}$$

where is the surface tension of mercury (484 mN m-1) and is the contact angle (141º) recommended by IUPAC (Sing et al, 1985).

The technique of mercury porosimetry consists of measuring the extent of mercury penetration into the pores of a solid as a function of the applied pressure. Automatic porosimeters are now in use for the routine examination of pore structures for catalysts, adsorbents, cements, refractory materials, and other materials. The measure range of porosimeters application extends from macropores to near of the limit between micropores and mesopores. Thus, there is an overlap with the gas adsorption method in the mesopore range.

#### **4. Gas adsorption**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

<sup>1</sup> <sup>1</sup> (1)

*Hg* is Hg density, respectively.

38 Characterization Techniques and Applications in the Wastewater Treatment

There are several "densities" related with activated carbons. These can be mentioned as:




*He Hg*

In preparation of charcoal, these values have been studied for different temperatures and times of preparation of charcoal (Durán-Valle et al., 2006; Pastor-Villegas & Durán-Valle,

The pores of solids are of different kinds. The individual pores may vary in size and in shape. With respect to the shape, in activated carbons, the predominant type is the slit-shape pore. But, the width of the pores is also of special interest for many purposes. A classification of pores according to their average width, which was adopted by the IUPAC

In recent years, the micropore range has been subdivided into very narrow pores (until 0.8 nm) or **ultramicropores**, where the enhancement of interaction potential is caused by the similarity in size between the pore and molecules, and **supermicropores**, which have a width (0.8 to 2.0 nm) between ultramicropores and mesopores (Gregg & Sing, 1982). Carbon-based materials usually have a bimodal pore size distribution, with one dominant peak being less than approximately 2 nm and the other major peak usually greater than 50

The volume of macropores it is usually on the order of 0.2-0.5 cm3 g-1, but the associated area is very small, on the order of 0.5 m2 g-1, which is negligible in an activated carbon (Do, 1998). Macropores are not important for the adsorption capacity, but their importance is because they act as transport pores to the meso- and micropores. Mesopores have a volume in the

*He* is the He density, and

**2. Density measurements and pore volume** 

pores; and c) space between particles.

where *V* is the pore volume,

2002).

**3. Porosimetry** 

nm (Do et al., 2008).

surface tension maintains Hg out of pores.

density gives a measure of the density of the carbon structure.

(IUPAC, 1972; Sing et al., 1985) is shown in Table 1.

The total volume of pores can be calculated from Hg and He densities by:

*V*

The ability to adsorb and desorb gases from the coals has been known for a long time (Scheele, 1780). A large amount of the information about the physical structure of a surface (i.e., specific surface and pores) comes from the amount of gas adsorbed on this surface as a function of gas pressure at a given temperature. Mercury porosimetry and gas adsorption are complementary techniques: porosimetry can measure mesopores and macropores, and gas adsorption measures micropores and mesopores.

The curves derived from these experiments are called **adsorption isotherms**. They can be used to determine thermodynamic parameters (e.g., heat of adsorption), the pore distribution, and

There are a lot of theoretical models applied on gas isotherms data, which allow obtaining physical characterization of carbon surfaces (Do et al, 2008). Some of the most used are cited

Techniques Employed in the Physicochemical Characterization of Activated Carbons 41

Mesopore size

and Dubinin-Astakhov (DA) Micropore volume Dubinin et al. (1947)

distribution

(BET) Surface area Brunauer et al. (1938)

One of the most used is that proposed by Brunauer, Emmett, and Teller: the BET model (Brunauer et al., 1938). This model is a two-parameter adsorption equation of the form

1 1

*<sup>0</sup>* is the monolayer capacity, and *c* is a constant (at isotherm temperature) that depends on

*0c* and intercept 1/

recommended pressure range is between 0.05 and 0.35 *P/P0* and from 0.02 to 0.12 for type I. If the molecular area occupied by the adsorbed gas is known, the surface area can be

interaction. When *c* increases, the interaction is stronger, relative to interactions between molecules of adsorbate, or, in other words, the isotherm type changes from type III (low *c*) to type II (medium *c*) and, finally, type I (high value of *c*). Care should be taken in analysing data, since type III and type V isotherms are not adequate for this mathematical approach.

The most used gas is N2 (molecular area, 0.162 nm2) at 77 K, but other vapors have been employed from time to time. The different molecular sizes (and shapes) cause that not all gases can access at the same pores. It is evident that this procedure must lead to anomalous results for the area of a given solid if different gases are used. Prior to the determination of an isotherm, all physisorbed material must be removed from the surface. This is achieved by exposure of the solid to high vacuum and heat. The exact temperature and residual pressure

*P P c c*

*<sup>0</sup>*. The value of *c* gives information about the adsorbate-adsorbent

Langmuir Surface area Langmuir (1918)

<sup>0</sup> <sup>0</sup> <sup>0</sup> <sup>0</sup>

*P P c*

(NLDFT or DFT) Pore size distribution Olivier (1995)

distribution Barret et al. (1951)

Hovarth & Kawazoe

(3)

is the adsorbed quantity at pressure *P*,

*0c*. For type II and IV isotherms, the

(*P0-P*)] versus *P/P0* yields a

(1983)

Model Determined parameter Reference

in Table 2.

(BJH)

Barret, Joyner and Halenda

Dubinin-Radushkevich (DR)

Density Functional Theory

(Gregg & Sing, 1982):

calculated from

Brunauer, Emmett and Teller

Horvarth-Kawazoe (HK) Micropore size

Table 2. Most common isotherm models used in gas adsorption.

*P*

the heat of condensation the heat of adsorption. A plot of *P*/[

where *P0* is the saturation pressure of vapor used,

(near) straight line with slope (*c*-1)/

(Gregg & Sing, 1982): of

can condition the final results.

the surface area. The IUPAC recommends a classification based on six types of isotherms these are shown in Figure 1. Types I to V were proposed by Brunauer, Deming, Deming, and Teller (Brunauer et al., 1940) and they are referred to as BDDT. Type VI was subsequently added (Gregg & Sing, 1982). There are a considerable number of borderline cases that are difficult to assign to one group rather than another.

Figure 1. Types of adsorption isotherms according to IUPAC classifications.

Type I isotherms are characteristics of the existence of only strong interactions between the adsorbate and adsorbent, which explains the high adsorption at low relative pressure. In activated carbons, this is due to the existence of micropores. If the isotherm is clearly of type I, the carbon is called "microporous carbon," and it can be assumed that most of the porosity is formed by pores whose widths less than 2 nm. This isotherm is very common in activated carbons. The isotherms of type II are generally associated to non-porous solids (Gregg & Sing, 1982). But, if the activated carbon has a wide distribution of pore widths (i.e., micropores and mesopores of different widths), the isotherm obtained can be similar to type II but with higher gas adsorption (Yates, 2003). In these cases, it must be thought that this isotherm is a combination of types I and IV. Pure type II represents the multilayer adsorption of a vapor into macropores or external surface. Type IV is an isotherm characteristic of a mesoporous solid and the hysteresis is due to capillary condensation into mesopores. Isotherms types III and V are characteristics for systems where the adsorbentadsorbate interaction is weak compared with adsorbate-adsorbate interactions. As activated carbons are a universal adsorbent and the interactions with adsorbate are never weak, then these isotherms are not frequently found in activated carbons. The same condition applies to type VI which is of theoretical interest but relatively rare in activated carbons.

40 Characterization Techniques and Applications in the Wastewater Treatment

the surface area. The IUPAC recommends a classification based on six types of isotherms these are shown in Figure 1. Types I to V were proposed by Brunauer, Deming, Deming, and Teller (Brunauer et al., 1940) and they are referred to as BDDT. Type VI was subsequently added (Gregg & Sing, 1982). There are a considerable number of borderline

cases that are difficult to assign to one group rather than another.

Figure 1. Types of adsorption isotherms according to IUPAC classifications.

type VI which is of theoretical interest but relatively rare in activated carbons.

Type I isotherms are characteristics of the existence of only strong interactions between the adsorbate and adsorbent, which explains the high adsorption at low relative pressure. In activated carbons, this is due to the existence of micropores. If the isotherm is clearly of type I, the carbon is called "microporous carbon," and it can be assumed that most of the porosity is formed by pores whose widths less than 2 nm. This isotherm is very common in activated carbons. The isotherms of type II are generally associated to non-porous solids (Gregg & Sing, 1982). But, if the activated carbon has a wide distribution of pore widths (i.e., micropores and mesopores of different widths), the isotherm obtained can be similar to type II but with higher gas adsorption (Yates, 2003). In these cases, it must be thought that this isotherm is a combination of types I and IV. Pure type II represents the multilayer adsorption of a vapor into macropores or external surface. Type IV is an isotherm characteristic of a mesoporous solid and the hysteresis is due to capillary condensation into mesopores. Isotherms types III and V are characteristics for systems where the adsorbentadsorbate interaction is weak compared with adsorbate-adsorbate interactions. As activated carbons are a universal adsorbent and the interactions with adsorbate are never weak, then these isotherms are not frequently found in activated carbons. The same condition applies to There are a lot of theoretical models applied on gas isotherms data, which allow obtaining physical characterization of carbon surfaces (Do et al, 2008). Some of the most used are cited in Table 2.


Table 2. Most common isotherm models used in gas adsorption.

One of the most used is that proposed by Brunauer, Emmett, and Teller: the BET model (Brunauer et al., 1938). This model is a two-parameter adsorption equation of the form (Gregg & Sing, 1982):

$$\frac{P}{\sigma(P\_0 - P)} = \frac{1}{\sigma\_0 c} + \frac{c - 1}{\sigma\_0 c} \frac{P}{P\_0} \tag{3}$$

where *P0* is the saturation pressure of vapor used, is the adsorbed quantity at pressure *P*, *<sup>0</sup>* is the monolayer capacity, and *c* is a constant (at isotherm temperature) that depends on the heat of condensation the heat of adsorption. A plot of *P*/[(*P0-P*)] versus *P/P0* yields a (near) straight line with slope (*c*-1)/*0c* and intercept 1/*0c*. For type II and IV isotherms, the recommended pressure range is between 0.05 and 0.35 *P/P0* and from 0.02 to 0.12 for type I. If the molecular area occupied by the adsorbed gas is known, the surface area can be calculated from *<sup>0</sup>*. The value of *c* gives information about the adsorbate-adsorbent interaction. When *c* increases, the interaction is stronger, relative to interactions between molecules of adsorbate, or, in other words, the isotherm type changes from type III (low *c*) to type II (medium *c*) and, finally, type I (high value of *c*). Care should be taken in analysing data, since type III and type V isotherms are not adequate for this mathematical approach. form (Gregg & Sing, 1982): this

The most used gas is N2 (molecular area, 0.162 nm2) at 77 K, but other vapors have been employed from time to time. The different molecular sizes (and shapes) cause that not all gases can access at the same pores. It is evident that this procedure must lead to anomalous results for the area of a given solid if different gases are used. Prior to the determination of an isotherm, all physisorbed material must be removed from the surface. This is achieved by exposure of the solid to high vacuum and heat. The exact temperature and residual pressure can condition the final results.

and pore structure (Pastor-Villegas et al., 1998). There are two types of elemental analysis: organic and inorganic. The organic elemental analysis is accomplished by combustion analysis and generally determines carbon, hydrogen, nitrogen, sulphur, and, by difference,

Techniques Employed in the Physicochemical Characterization of Activated Carbons 43


Table 4. Information about the chemistry of carbon obtained from organic elemental

The inorganic elemental analysis yields information about inorganic material (ashes in carbon materials, supported catalysts) and can be carried out by various techniques, based mainly on X-ray, electron, or mass spectroscopy. Related with elemental analysis is radioactive characterization (Rubio-Montero et al., 2009), this is a promising method to

One of the most influential variables in the adsorption in solution is the pH, since this parameter can change the sign (or presence) of charges onto the adsorbate. On the surface of activated carbon, the predominant charge (positive or negative) depends on the acidic or basic character of the adsorbent. Therefore, it is important to study the presence of acidic or

A global measurement of the acidity/basicity of a carbon is the point of zero charge (PZC) at which the surface charge density is 0 (IUPAC, 1997). It is usually determined in relation to a disolution's pH: the pH of the solution at equilibrium with a solid when the solid exhibits zero net electrical charge on the surface. A very similar concept is the isoelectric point (IEP), which requires that the charge is 0 in the entire solid, not only on the surface. Generally, IEP is very similar to PZC. The PZC can be obtained from acid-base titrations of dispersions and monitoring the electrophoretic mobility of the particles and the solution pH. The titration of




oxygen; observations about each one are reported in Table 4.

Element Low content High content


(HHV)

C

### **5. Proximate analysis**

Proximate analysis is one of the thermal analysis techniques. These are analytical techniques in which a physical property is measured with a temperature-programmed variation. In this case, the property measured is the weight.

Proximate analysis provides an approach to estimate the content of: a) moisture; b) volatile matter; c) fixed carbon; and d) ash. There are some standard methods (for example, ASTM, DIN, UNE), but the analysis is usually carried out in an automated thermogravimetric system. Moisture measurements refer to the matter volatilized until near 373 K in an inert atmosphere, mostly water. Volatile matter is determined by the same procedure but in a temperature range of 373 to 1223 K. Fixed carbon is the material burned in air at 1223 K in a third step and is made of the more stable organic structures. Lastly, the non-combustible matter is the ash. Generally, the composition of ash, fixed carbon, and volatile matter are given on a dry basis. The representation of weight versus temperature (or time) also gives information about the thermal stability of the activated carbon.


### **6. Elemental analysis**

Elemental analysis is the primary method to obtain knowledge about carbon chemistry (Bandosz, 2009). This technique does not provide details on functional groups but at least gives information about heteroatom content and it can provide approximate information on chemical structure, see Table 3 (Chingombe et al., 2005), graphene size (Duran-Valle, 2006), and pore structure (Pastor-Villegas et al., 1998). There are two types of elemental analysis: organic and inorganic. The organic elemental analysis is accomplished by combustion analysis and generally determines carbon, hydrogen, nitrogen, sulphur, and, by difference, oxygen; observations about each one are reported in Table 4.


### **7. Acid/base titration**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

42 Characterization Techniques and Applications in the Wastewater Treatment

Proximate analysis is one of the thermal analysis techniques. These are analytical techniques in which a physical property is measured with a temperature-programmed variation. In this

Proximate analysis provides an approach to estimate the content of: a) moisture; b) volatile matter; c) fixed carbon; and d) ash. There are some standard methods (for example, ASTM, DIN, UNE), but the analysis is usually carried out in an automated thermogravimetric system. Moisture measurements refer to the matter volatilized until near 373 K in an inert atmosphere, mostly water. Volatile matter is determined by the same procedure but in a temperature range of 373 to 1223 K. Fixed carbon is the material burned in air at 1223 K in a third step and is made of the more stable organic structures. Lastly, the non-combustible matter is the ash. Generally, the composition of ash, fixed carbon, and volatile matter are given on a dry basis. The representation of weight versus temperature (or time) also gives

The proximate analysis is susceptible of variations in the thermal treatment. Generally, when temperature or time increases, the volatile matter content decreases. The effect of this is that both the ash content and the fixed carbon content increase as a consequence of the concentration of the inorganic fraction and carbon in charcoal (Duran-Valle et al., 2006).

 As in the elemental analysis, this technique does not give accurate information about functional groups but can provide limited information on chemical structure (see Table 3). A better and related technique is thermal programmed desorption, in which desorbed

**5. Proximate analysis** 

case, the property measured is the weight.

information about the thermal stability of the activated carbon.

species produced at heating are analyzed (see below).

Volatile matter High graphitization grade

Fixed carbon Low graphitization grade

Moisture High HHV

**6. Elemental analysis** 

Element Low content High content

Low amount of functional groups

High amount of functional groups

Table 3. Information about the chemistry of carbon obtained from proximate analysis.

Elemental analysis is the primary method to obtain knowledge about carbon chemistry (Bandosz, 2009). This technique does not provide details on functional groups but at least gives information about heteroatom content and it can provide approximate information on chemical structure, see Table 3 (Chingombe et al., 2005), graphene size (Duran-Valle, 2006),

Ash --- Low HHV

Low graphitization grade

A global measurement of the acidity/basicity of a carbon is the point of zero charge (PZC) at which the surface charge density is 0 (IUPAC, 1997). It is usually determined in relation to a disolution's pH: the pH of the solution at equilibrium with a solid when the solid exhibits zero net electrical charge on the surface. A very similar concept is the isoelectric point (IEP), which requires that the charge is 0 in the entire solid, not only on the surface. Generally, IEP is very similar to PZC. The PZC can be obtained from acid-base titrations of dispersions and monitoring the electrophoretic mobility of the particles and the solution pH. The titration of

Figure 3. Determination of PZC by Valente-Nabais & Carrott method. Variation of activated

Techniques Employed in the Physicochemical Characterization of Activated Carbons 45

TPD is a thermal analysis method widely used for the characterization of activated carbons. In this technique, a sample is heated in a carrier gas, to induce thermal desorption of adsorbed species or thermal decomposition. The desorbed products are analyzed by several methods. By heating, the oxygenated groups are thermally decomposed, releasing CO, CO2, and H2O at different temperatures. The groups can be identified by decomposition temperature and type of gas and can be quantified by the areas of peaks. The major difficulty is the identification of each surface group, because in activated carbons TPD spectra show composite and broad peaks of all gases released. An application of this

There are a set of techniques that measure the heat involved in a process (Bandosz, 2009). Such techniques have been used to estimate some aspects of the physical and the chemical structure of activated carbons. Immersion calorimetry provides a measurement of the energy involved in the interaction of molecules of a liquid with the surface of activated carbon. The use of several liquids with different polarities can be related with the hydrophobic and hydrophilic nature of the surface. The enthalpy of immersion of carbonaceous materials into water can give information about primary adsorption centers that are related to the oxygen content (Stoeckli et al., 1983). The differential scanning calorimetry (DSC) measures the difference in the amount of heat required to increase the temperature of a sample and a reference sample as a function of temperature. A similar technique is the differential thermal analysis; in this, the difference in temperature between sample and reference is the parameter measured. Both techniques can be used to evaluate

carbon w/v.

**8. Thermal Programmed Desorption (TPD)** 

**9. Calorimetric Techniques** 

technique with several references is shown in (Figueiredo et al., 1999).

the thermal behavior of a charcoal (Duran-Valle et al., 2005).

several dispersions of activated carbons in aqueous solutions with different initial pHs is easier and cheaper. A plot of final pH versus initial pH of the solutions with and without activated carbon gives a cross that indicates the PZC (see Figure 2).

Figure 2. PZC measurement determined in several solutions at different initial pHs.

Another method is also mass titration with only a solution (whose pH in this method is irrelevant) and with at least 7% (w/v) activated carbon (Valente-Nabais & Carrot, 2006). The pH of the solution is approaching to the PZC when the carbon quantity increases. With 7% (w/v) of activated carbon, the equilibrium is reached. Then, the solution pH is the PZC of the adsorbent (see Figure 3).

A more detailed assessment of the acidity/basicity is performed by titration with several substances of different acidities. As an example, in the method proposed by Boehm (Boehm, 2002), the amount of oxygen-containing groups (carboxyl, lactonic, phenol, and others) was determined by adsorption neutralization with NaHCO3, Na2CO3, NaOH, and NaOCH2CH3 solutions, respectively. Also, the basic group content can be determined with HCl solution. This method, widely used, has several drawbacks. As in all classic titrations with solids (especially with microporous solids), the equilibrium time is very long. There may be functional groups with the same structure and very different acidities, or different functional groups with similar acidities (for example, 2,4-dinitrophenol and benzoic acid have a similar pKa). This prevents quantification of functional groups in its structure, although it could be realized by acid strength. Another failure is that functional groups containing other heteroatoms are considered as oxygen functional groups. The acidic or basic functional groups can be also characterized by immersion calorimetry (López-Ramón et al., 1999).

Figure 3. Determination of PZC by Valente-Nabais & Carrott method. Variation of activated carbon w/v.

#### **8. Thermal Programmed Desorption (TPD)**

TPD is a thermal analysis method widely used for the characterization of activated carbons. In this technique, a sample is heated in a carrier gas, to induce thermal desorption of adsorbed species or thermal decomposition. The desorbed products are analyzed by several methods. By heating, the oxygenated groups are thermally decomposed, releasing CO, CO2, and H2O at different temperatures. The groups can be identified by decomposition temperature and type of gas and can be quantified by the areas of peaks. The major difficulty is the identification of each surface group, because in activated carbons TPD spectra show composite and broad peaks of all gases released. An application of this technique with several references is shown in (Figueiredo et al., 1999).

#### **9. Calorimetric Techniques**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

44 Characterization Techniques and Applications in the Wastewater Treatment

several dispersions of activated carbons in aqueous solutions with different initial pHs is easier and cheaper. A plot of final pH versus initial pH of the solutions with and without

Figure 2. PZC measurement determined in several solutions at different initial pHs.

the adsorbent (see Figure 3).

et al., 1999).

Another method is also mass titration with only a solution (whose pH in this method is irrelevant) and with at least 7% (w/v) activated carbon (Valente-Nabais & Carrot, 2006). The pH of the solution is approaching to the PZC when the carbon quantity increases. With 7% (w/v) of activated carbon, the equilibrium is reached. Then, the solution pH is the PZC of

A more detailed assessment of the acidity/basicity is performed by titration with several substances of different acidities. As an example, in the method proposed by Boehm (Boehm, 2002), the amount of oxygen-containing groups (carboxyl, lactonic, phenol, and others) was determined by adsorption neutralization with NaHCO3, Na2CO3, NaOH, and NaOCH2CH3 solutions, respectively. Also, the basic group content can be determined with HCl solution. This method, widely used, has several drawbacks. As in all classic titrations with solids (especially with microporous solids), the equilibrium time is very long. There may be functional groups with the same structure and very different acidities, or different functional groups with similar acidities (for example, 2,4-dinitrophenol and benzoic acid have a similar pKa). This prevents quantification of functional groups in its structure, although it could be realized by acid strength. Another failure is that functional groups containing other heteroatoms are considered as oxygen functional groups. The acidic or basic functional groups can be also characterized by immersion calorimetry (López-Ramón

activated carbon gives a cross that indicates the PZC (see Figure 2).

There are a set of techniques that measure the heat involved in a process (Bandosz, 2009). Such techniques have been used to estimate some aspects of the physical and the chemical structure of activated carbons. Immersion calorimetry provides a measurement of the energy involved in the interaction of molecules of a liquid with the surface of activated carbon. The use of several liquids with different polarities can be related with the hydrophobic and hydrophilic nature of the surface. The enthalpy of immersion of carbonaceous materials into water can give information about primary adsorption centers that are related to the oxygen content (Stoeckli et al., 1983). The differential scanning calorimetry (DSC) measures the difference in the amount of heat required to increase the temperature of a sample and a reference sample as a function of temperature. A similar technique is the differential thermal analysis; in this, the difference in temperature between sample and reference is the parameter measured. Both techniques can be used to evaluate the thermal behavior of a charcoal (Duran-Valle et al., 2005). with primary

**11. X-Ray Photoelectron Spectroscopy (XPS)** 

which depends on the equipment. The energy equation is:

Figure 4. Mechanism of X-Ray Photoelectron Spectroscopy.

the kinetic energy of the electron).

surface) can be carried out.

XPS (also known as ESCA, electron spectroscopy for chemical analysis) is a technique frequently used in surface chemistry. XPS measures the energy of internal atomic orbitals. This value is characteristic of each element, and so, XPS gives information about elemental composition. But, this value changes slightly with the electric charge on the atom. Therefore, XPS also gives information about functional groups in activated carbons. An important feature of this technique is that the analysis is limited to the surface (some nanometers). This feature can be positive (for surface chemistry studies) or negative (if surface contamination exits). This fact is typical of a spectroscopic technique that uses electrons in their mechanism, because the electrons interact with materials more than photons of the same energy, and so, electrons can pass through a smaller amount of material (in XPS, 0.4 – 4 nm, depending on

Techniques Employed in the Physicochemical Characterization of Activated Carbons 47

XPS uses monochromatic X-ray photons to excite an inner-shell electron. This electron can be extracted out of the atom, and its kinetic energy can be measured. The kinetic energy depends on the binding energy. The mechanism of the process is shown in Figure 4. An incident photon (given is clear color) of energy *hν* is absorbed by an atom, and an electron (given in dark color) placed in an orbital of bind energy Eb leaves the atom with a kinetic energy Ee. The energy of the photon is divided between the energy to translate the electron to the Fermi level (Eb), the kinetic energy, and a correction factor, the work function (w),

*wEEh*

All data except Eb are experimentally known, and Eb can be easily calculated. The intensity of the peaks is related to the concentration of the element, and quantitative analysis (of the

*eb* (4)

#### **10. Infrared Spectroscopy (FTIR)**

Infrared spectroscopy is a traditional method for structural analyses of organic compounds, where infrared radiation is absorbed selectively by the various bonds within a compound. Since FTIR spectroscopy can detect specific bonds in a material, then it is possible to know which functionalities exist on the surface of carbon. IR spectroscopy has been used to study, for example, the changes in the surface chemical structure of the carbon materials after oxidation (Chingombe et al., 2005; Moreno-Castilla et al., 2000; Pradhan & Sandle, 1999), reactions with alkali (Lillo-Ródenas et al., 2003), the carbonization and activation process (Pastor-Villegas et al., 1999), or in the chemical activation of wood (Solum et al., 1995). FTIR is mainly used as a qualitative technique for the analysis of the chemical structure of activated carbons and, sometimes, as quantitative technique (Bandosz, 2009). Two problems are associated with this technique—a) the opacity of carbons and b) the broad peaks because they are usually a sum of interactions of similar types of functional groups. This technique was used intensively on carbonaceous materials when equipments with Fourier transform (FT) were accessible. The FT allows an improvement over signal/noise rate, energy throughout, accuracy, and fast scans. This approach partially eliminated the opacity problem. Better results can be obtained with alternative techniques (López & Márquez, 2003) that allow reflection (rather than transmission) on activated carbon surfaces—for example, specular reflectance, diffuse reflectance (DRIFT), attenuated total reflectance (ATR), or photoacustic spectroscopy (FTIR-PAS). The assignment of the IR bands to different functional groups is made by comparison with adsorption/transmission bands of organic compounds (Bellamy, 1986; Smith, 1999). The width of the bands is due to the existence of several similar bands with a maximum at different frequencies, because they are affected by vicinal functionalities. Table 5 shows the approximate assignment of main bands in charcoals IR spectra.


Table 5. Assignment of bands in IR spectra of charcoals.

#### **11. X-Ray Photoelectron Spectroscopy (XPS)**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

aromatic hidrocarbons

olefines, methyl

46 Characterization Techniques and Applications in the Wastewater Treatment

Infrared spectroscopy is a traditional method for structural analyses of organic compounds, where infrared radiation is absorbed selectively by the various bonds within a compound. Since FTIR spectroscopy can detect specific bonds in a material, then it is possible to know which functionalities exist on the surface of carbon. IR spectroscopy has been used to study, for example, the changes in the surface chemical structure of the carbon materials after oxidation (Chingombe et al., 2005; Moreno-Castilla et al., 2000; Pradhan & Sandle, 1999), reactions with alkali (Lillo-Ródenas et al., 2003), the carbonization and activation process (Pastor-Villegas et al., 1999), or in the chemical activation of wood (Solum et al., 1995). FTIR is mainly used as a qualitative technique for the analysis of the chemical structure of activated carbons and, sometimes, as quantitative technique (Bandosz, 2009). Two problems are associated with this technique—a) the opacity of carbons and b) the broad peaks because they are usually a sum of interactions of similar types of functional groups. This technique was used intensively on carbonaceous materials when equipments with Fourier transform (FT) were accessible. The FT allows an improvement over signal/noise rate, energy throughout, accuracy, and fast scans. This approach partially eliminated the opacity problem. Better results can be obtained with alternative techniques (López & Márquez, 2003) that allow reflection (rather than transmission) on activated carbon surfaces—for example, specular reflectance, diffuse reflectance (DRIFT), attenuated total reflectance (ATR), or photoacustic spectroscopy (FTIR-PAS). The assignment of the IR bands to different functional groups is made by comparison with adsorption/transmission bands of organic compounds (Bellamy, 1986; Smith, 1999). The width of the bands is due to the existence of several similar bands with a maximum at different frequencies, because they are affected by vicinal functionalities. Table 5 shows the approximate assignment of main bands

Wavenumber (cm-1) Assignment Structures

1770–1650 Stretching C=O Carbonyl

Table 5. Assignment of bands in IR spectra of charcoals.

1700–1600 Stretching C=C Olefinic structures 1650–1500 Stretching C=C Aromatic structures 1480–1420 Bending C-H Alifatic structures

1300–1200 Stretching C-O Unsaturated ethers 1160–1050 Stretching C-O Tertiary hydroxyl 1120–1070 Stretching C-O Secondary hydroxyl 1060–1000 Stretching C-O Primary hydroxyl 900–700 Bending out of the plane C-H Aromatic structures

of

3600–3000 Stretching O-H, N-H Hydroxyl, carboxilic acid 3000–2800 Stretching C-H Alifatic, olefinic and

1430–1360 Bending O-H and C-H Hydroxyl, carboxilic acid,

**10. Infrared Spectroscopy (FTIR)** 

in charcoals IR spectra.

XPS (also known as ESCA, electron spectroscopy for chemical analysis) is a technique frequently used in surface chemistry. XPS measures the energy of internal atomic orbitals. This value is characteristic of each element, and so, XPS gives information about elemental composition. But, this value changes slightly with the electric charge on the atom. Therefore, XPS also gives information about functional groups in activated carbons. An important feature of this technique is that the analysis is limited to the surface (some nanometers). This feature can be positive (for surface chemistry studies) or negative (if surface contamination exits). This fact is typical of a spectroscopic technique that uses electrons in their mechanism, because the electrons interact with materials more than photons of the same energy, and so, electrons can pass through a smaller amount of material (in XPS, 0.4 – 4 nm, depending on the kinetic energy of the electron).

XPS uses monochromatic X-ray photons to excite an inner-shell electron. This electron can be extracted out of the atom, and its kinetic energy can be measured. The kinetic energy depends on the binding energy. The mechanism of the process is shown in Figure 4. An incident photon (given is clear color) of energy *hν* is absorbed by an atom, and an electron (given in dark color) placed in an orbital of bind energy Eb leaves the atom with a kinetic energy Ee. The energy of the photon is divided between the energy to translate the electron to the Fermi level (Eb), the kinetic energy, and a correction factor, the work function (w), which depends on the equipment. The energy equation is:

$$h\,\nu = E\_{\flat} + E\_{c} + \text{\textquotedblleft}w\tag{4}$$

All data except Eb are experimentally known, and Eb can be easily calculated. The intensity of the peaks is related to the concentration of the element, and quantitative analysis (of the surface) can be carried out.

Figure 4. Mechanism of X-Ray Photoelectron Spectroscopy.

100

*g* (5)

values (maximum near 20 degrees), and it is indicative of the

*g*(%) (6)

3354.03440.0

where 0.3440 (nm) is the interlayer spacing of the non-graphitized carbon and 0.3354 (nm) is

Other method uses the surface under two peaks (Johnson, 1959). The first of these peaks (A)

amorphous nature of the material. The second peak (C) is situated near 25 degrees, is higher

*A <sup>C</sup> KI I I*

There are other techniques of characterization of activated carbons than X-ray radiation, but they are not as commonly used as XRD or XPS. Some of these techniques are described below.

XRF is the emission of characteristic X-ray radiation from a material that has been excited by bombarding it with X-ray or gamma photons. The term fluorescence is applied when the absorption of radiation of a specific energy results in the emission of radiation of a different (generally lower) energy. This technique is widely used for elemental analysis, but it gives more limited information that obtained in XPS. The mechanism of this phenomenon is shown in Figure 5, which can be considered as a continuation from Figure 4b. Later than when an electron is expulsed of an atom absorbing the energy of a photon (Figure 5a), a hole is created on the lower orbital. An electron of a higher orbital "falls" into the lower orbital (Figure 5b), and energy is released in the form of a photon (Figure 5c). The energy of this photon is equal to the energy difference of the two orbitals involved, and this quantity is

where *IC* is the integrate of peak C, *IA* is the integrate of peak A, and *K* is a constant.

*A*

and narrower, and indicates the presence of crystallinity. The equation used is:

3440.0 (%) )002( *<sup>d</sup>*

Techniques Employed in the Physicochemical Characterization of Activated Carbons 49

the interlayer spacing of an ideal-type graphite crystallite.

is broad and situated at low *2*

**13. Other X-Ray techniques** 

characteristic of this element.

Figure 5. Mechanism of X-ray fluorescence.

In activated carbons, XPS is used to characterize surface functionalities (Bandosz, 2009; Chingombe et al., 2005; Moreno-Castilla et al., 2000) employing binding energies of the C 1s, N 1s, and O 1s photoelectrons (Figueiredo et al., 1999). A comparison with elemental analyses can yield information about different compositions in the surface and into the bulk (Figueiredo et al., 1999).

Table 6 shows an interpretation of peaks of C 1s XPS spectra. Assignment of peaks in N 1s spectra is more difficult due to the large variety of species (with different oxidation states) that nitrogen atoms can form. The value of binding energy varies between 399 eV (reduced form of nitrogen, as amines) to 404 eV (oxidized form of nitrogen, as nitro groups or nitrate). The assignment of peaks for O 1s spectra is easier, because generally only three bands can be distinguished: near 532 eV (double bond C=O), 534 eV (single bond C-O), and 536 eV (water occluded) (Lin et al., 2008).

Two similar techniques are UPS (ultraviolet photoelectron spectroscopy), where photons have energy until 50 eV which allows to be used to study external orbitals (Raymundo-Piñero et al., 2002); and SXPS (soft X-ray photoelectron spectroscopy), which uses photons with energy from 50 to 150 eV.


Table 6. Assignment of peaks in C 1s XPS spectra.

#### **12. X-Ray diffraction (XRD)**

Activated carbons contain short-range ordered structures, then XRD can provide details about the crystallites or micrographites into the carbon structure, including the disordered and defective features (Burian et al., 2005). This information is obtained from the distribution of scattered radiation using X-rays. The observed diffraction pattern may be converted to structural data, so XRD is used not only to estimate crystallite size or graphitization degree in carbonaceous materials (Biniak et al., 2010; Pradhan & Sandle, 1999) but also used to characterize the inorganic material (Pastor-Villegas et al., 1999). The degree of graphitization is an important parameter, since it reflects the transition extent of carbon material from turbostratic to graphitic structure, and determines some properties of the material (Hussain et al., 2000; Zou et al., 2003).

Generally, the (0 0 2) line is used to determine the interlayer spacing *d*(0 0 2) according to the Bragg equation. A method for calculating the degree of graphitization (*g*) can be done by using the following equation (Maire & Mering, 1970):

$$\log(\%) = \frac{0.3440 - d\_{(002)}}{0.3440 - 0.3354} \times 100\tag{5}$$

where 0.3440 (nm) is the interlayer spacing of the non-graphitized carbon and 0.3354 (nm) is the interlayer spacing of an ideal-type graphite crystallite.

Other method uses the surface under two peaks (Johnson, 1959). The first of these peaks (A) is broad and situated at low *2* values (maximum near 20 degrees), and it is indicative of the amorphous nature of the material. The second peak (C) is situated near 25 degrees, is higher and narrower, and indicates the presence of crystallinity. The equation used is:

$$\log(\%) = \frac{I\_C}{I\_A} + KI\_A \tag{6}$$

where *IC* is the integrate of peak C, *IA* is the integrate of peak A, and *K* is a constant.

#### **13. Other X-Ray techniques**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

48 Characterization Techniques and Applications in the Wastewater Treatment

In activated carbons, XPS is used to characterize surface functionalities (Bandosz, 2009; Chingombe et al., 2005; Moreno-Castilla et al., 2000) employing binding energies of the C 1s, N 1s, and O 1s photoelectrons (Figueiredo et al., 1999). A comparison with elemental analyses can yield information about different compositions in the surface and into the bulk

Table 6 shows an interpretation of peaks of C 1s XPS spectra. Assignment of peaks in N 1s spectra is more difficult due to the large variety of species (with different oxidation states) that nitrogen atoms can form. The value of binding energy varies between 399 eV (reduced form of nitrogen, as amines) to 404 eV (oxidized form of nitrogen, as nitro groups or nitrate). The assignment of peaks for O 1s spectra is easier, because generally only three bands can be distinguished: near 532 eV (double bond C=O), 534 eV (single bond C-O), and 536 eV (water

Two similar techniques are UPS (ultraviolet photoelectron spectroscopy), where photons have energy until 50 eV which allows to be used to study external orbitals (Raymundo-Piñero et al., 2002); and SXPS (soft X-ray photoelectron spectroscopy), which uses photons

285.0 Aromatics and aliphatics structures. Carbon atoms bond to hydrogen or carbon atoms

Activated carbons contain short-range ordered structures, then XRD can provide details about the crystallites or micrographites into the carbon structure, including the disordered and defective features (Burian et al., 2005). This information is obtained from the distribution of scattered radiation using X-rays. The observed diffraction pattern may be converted to structural data, so XRD is used not only to estimate crystallite size or graphitization degree in carbonaceous materials (Biniak et al., 2010; Pradhan & Sandle, 1999) but also used to characterize the inorganic material (Pastor-Villegas et al., 1999). The degree of graphitization is an important parameter, since it reflects the transition extent of carbon material from turbostratic to graphitic structure, and determines some properties of the

Generally, the (0 0 2) line is used to determine the interlayer spacing *d*(0 0 2) according to the Bragg equation. A method for calculating the degree of graphitization (*g*) can be done by

Assignment

286.0 Single C-O bond (alcohol, ether) 287.5 Double C=O bond (carbonyl) 289.0 O-C=O (carboxyl, ester)

286.0 Single C-O bond (alcohol, ether) the

290.5 Carbonate, CO2 291.5 Plasmon

Table 6. Assignment of peaks in C 1s XPS spectra.

material (Hussain et al., 2000; Zou et al., 2003).

using the following equation (Maire & Mering, 1970):

(Figueiredo et al., 1999).

occluded) (Lin et al., 2008).

with energy from 50 to 150 eV.

**12. X-Ray diffraction (XRD)** 

Binding energy (eV) (approximate)

There are other techniques of characterization of activated carbons than X-ray radiation, but they are not as commonly used as XRD or XPS. Some of these techniques are described below.

#### **13.1 X-ray fluorescence (XRF)**

XRF is the emission of characteristic X-ray radiation from a material that has been excited by bombarding it with X-ray or gamma photons. The term fluorescence is applied when the absorption of radiation of a specific energy results in the emission of radiation of a different (generally lower) energy. This technique is widely used for elemental analysis, but it gives more limited information that obtained in XPS. The mechanism of this phenomenon is shown in Figure 5, which can be considered as a continuation from Figure 4b. Later than when an electron is expulsed of an atom absorbing the energy of a photon (Figure 5a), a hole is created on the lower orbital. An electron of a higher orbital "falls" into the lower orbital (Figure 5b), and energy is released in the form of a photon (Figure 5c). The energy of this photon is equal to the energy difference of the two orbitals involved, and this quantity is characteristic of this element.

Figure 5. Mechanism of X-ray fluorescence.

**14. Micro Raman spectroscopy** 

**15. Nuclear Magnetic Resonance (NMR)** 

these compounds have atoms that are different from carbon.

structure.

**16. Conclusions** 

carbonaceous materials is needed.

carbons to better understand their properties.

applications.

Raman spectroscopy is used to study vibrational and rotational modes in a system. It is related with FTIR, and both techniques are usually complementary. Laser Raman spectroscopy is used on carbonaceous materials to evaluate the degree of graphitization (Zou et al., 2003) and not for functional groups determination. Micro laser Raman spectroscopy allows to analyze a microscopic surface area of interest. It is an alternative technique to XRD for studying the graphitization extension of a carbonaceous material (Cuesta et al., 1994). In Raman spectra of most activated carbons, two peaks are generally obtained: 1360 and 1580 cm-1. The last one corresponds to graphite structure, and the 1360 cm-1 is correlated with a disordered carbon structure. The ratio of the integrated intensities (I1360/I1580) has been considered to be a good parameter to estimate the disorder in the

Techniques Employed in the Physicochemical Characterization of Activated Carbons 51

NMR is a technique based on measurements of absorption of electromagnetic radiation related with atom nuclei into a magnetic shield. Its use in activated carbon analysis (and other solids) has increased due to the magic-angle spinning (MAS) method that solves the problems of lack of resolution due to the solid state. Generally, the 13C spectrum is the most used. The obtained information includes the hybridization of carbon atoms and the presence of oxygenated functional groups. 13C-NMR can give the aromatic-to-aliphatic carbon ratio and is useful to study changes in surface chemistry (Solum et al., 1995), including heteroatoms. Also, NMR can be used to study compounds adsorbed on carbon surfaces if

Activated carbons have been used for a long time as adsorbents. It is now recognized that activated carbons offer unparallel flexibility in tailoring their physical and chemical properties to specific needs, thus showing the remarkably wide range of potential

The simultaneous use of several physicochemical characterization techniques is very common, and there are a lot of examples in publications. This is due to no one technique may provide all the necessary information about surfaces, together with the extremely complex structures (physical and chemical) of carbon. However, the structure of these materials is not well understood, and more research about the analysis of porous

Traditionally, techniques used in the study of physical structure and those techniques used in the study of chemical structure have been distinguished. But, it has been shown that often both structures are related. It is advisable to conduct a comprehensive study of the activated

#### **13.2 Small-angle X-ray scattering (SAXS)**

Small-angle X-ray scattering is a technique where the scattering of X-ray photons by a sample that has inhomogeneities in the nm scale is detected at very low angles. This angular range contains information about pores in activated carbon (Bóta et al., 1997). This technique yields information about physical structure, as XRD, but not about composition, as XPS.

#### **13.3 EDX-SEM**

A variation of XRF is the energy-dispersive X-ray spectroscopy (EDX), which is commonly connected to scanning electron microscopes (SEMs). The union of these two techniques allows a point elemental analysis of a surface and also makes a "map" of elemental composition of a surface. This technique is mainly used to study the content and dispersion of metals on a carbon surface.

With illustrative purposes, Figure 6 shows an SEM image (top left) of an activated carbon doped with a sulphur-containing dye. The next figures are the same sample but "tuned" in an element. It can be seen at some points that the concentration of several heteroatoms is high, and these points can be assigned to mineral matter.

Figure 6. EDX-SEM images of an activated carbon treated with acid blue 25. Image courtesy of Servicio de Apoyo a la Investigación de la Universidad de Extremadura (Badajoz, Spain). Sample supplied by the Instituto Tecnológico de Aguascalientes (Aguascalientes, Mexico).

#### **14. Micro Raman spectroscopy**

Lignocellulosic Precursors Used in the Synthesis of Activated Carbon-

50 Characterization Techniques and Applications in the Wastewater Treatment

Small-angle X-ray scattering is a technique where the scattering of X-ray photons by a sample that has inhomogeneities in the nm scale is detected at very low angles. This angular range contains information about pores in activated carbon (Bóta et al., 1997). This technique yields information about physical structure, as XRD, but not about composition, as XPS.

A variation of XRF is the energy-dispersive X-ray spectroscopy (EDX), which is commonly connected to scanning electron microscopes (SEMs). The union of these two techniques allows a point elemental analysis of a surface and also makes a "map" of elemental composition of a surface. This technique is mainly used to study the content and dispersion

With illustrative purposes, Figure 6 shows an SEM image (top left) of an activated carbon doped with a sulphur-containing dye. The next figures are the same sample but "tuned" in an element. It can be seen at some points that the concentration of several heteroatoms is

Figure 6. EDX-SEM images of an activated carbon treated with acid blue 25. Image courtesy of Servicio de Apoyo a la Investigación de la Universidad de Extremadura (Badajoz, Spain). Sample supplied by the Instituto Tecnológico de Aguascalientes (Aguascalientes, Mexico).

**13.2 Small-angle X-ray scattering (SAXS)** 

high, and these points can be assigned to mineral matter.

**13.3 EDX-SEM** 

of metals on a carbon surface.

Raman spectroscopy is used to study vibrational and rotational modes in a system. It is related with FTIR, and both techniques are usually complementary. Laser Raman spectroscopy is used on carbonaceous materials to evaluate the degree of graphitization (Zou et al., 2003) and not for functional groups determination. Micro laser Raman spectroscopy allows to analyze a microscopic surface area of interest. It is an alternative technique to XRD for studying the graphitization extension of a carbonaceous material (Cuesta et al., 1994). In Raman spectra of most activated carbons, two peaks are generally obtained: 1360 and 1580 cm-1. The last one corresponds to graphite structure, and the 1360 cm-1 is correlated with a disordered carbon structure. The ratio of the integrated intensities (I1360/I1580) has been considered to be a good parameter to estimate the disorder in the structure.

#### **15. Nuclear Magnetic Resonance (NMR)**

NMR is a technique based on measurements of absorption of electromagnetic radiation related with atom nuclei into a magnetic shield. Its use in activated carbon analysis (and other solids) has increased due to the magic-angle spinning (MAS) method that solves the problems of lack of resolution due to the solid state. Generally, the 13C spectrum is the most used. The obtained information includes the hybridization of carbon atoms and the presence of oxygenated functional groups. 13C-NMR can give the aromatic-to-aliphatic carbon ratio and is useful to study changes in surface chemistry (Solum et al., 1995), including heteroatoms. Also, NMR can be used to study compounds adsorbed on carbon surfaces if these compounds have atoms that are different from carbon.

#### **16. Conclusions**

Activated carbons have been used for a long time as adsorbents. It is now recognized that activated carbons offer unparallel flexibility in tailoring their physical and chemical properties to specific needs, thus showing the remarkably wide range of potential applications.

The simultaneous use of several physicochemical characterization techniques is very common, and there are a lot of examples in publications. This is due to no one technique may provide all the necessary information about surfaces, together with the extremely complex structures (physical and chemical) of carbon. However, the structure of these materials is not well understood, and more research about the analysis of porous carbonaceous materials is needed.

Traditionally, techniques used in the study of physical structure and those techniques used in the study of chemical structure have been distinguished. But, it has been shown that often both structures are related. It is advisable to conduct a comprehensive study of the activated carbons to better understand their properties.

[14] Do, D.D.; Ustinov, E.A. & Do, H.D. (2008). Porous Texture Characterization from Gas-Solid Adsorption. In: *Adsorption by Carbons*. Bottani, E.J. & Tascón, J.M.D. (Eds.). pp.

Techniques Employed in the Physicochemical Characterization of Activated Carbons 53

[15] Dubinin, M.M., Zaverina, E.D. & Radushkevich, L.V. (1947). Sorption and structure of active carbons. I. Adsorption of organic vapors. *Zhurnal Fizicheskoi Khimii,* Vol. 21,

[16] Durán-Valle, C.J. (2006). Geometrical relationship between elemental composition and molecular size in carbonaceous materials. *Applied Surface Science,* Vol. 252, No. 17, (June

[17] Durán-Valle, C.J., Gómez-Corzo, M., Gómez-Serrano, V., Pastor-Villegas, J. & Rojas-Cervantes, M.L. (2006). Preparation of charcoal from cherry stones. *Applied Surface* 

[18] Durán-Valle, C.J., Gómez-Corzo, M., Pastor-Villegas, J. & Gómez-Serrano, V. (2005). Study of cherry stones as raw material in preparation of carbonaceous adsorbents. *Journal of Analytical and Applied Pyrolysis*, Vol. 73, No. 1, (March 2005), pp. (59-67), ISSN 0165-2370. [19] Figueiredo, J.L.; Pereira, M.F.R.; Freitas, M.M.A. & Orfao, J.J.M. (1999). Modification of the surface chemistry of activated carbons. *Carbon,* Vol. 37, No. 9, (1999), pp. (1379–

[20] Gregg, S.J. & Sing, K.S.W. (1982). *Adsorption, Surface Area and Porosity*. 2nd edition.

[21] Hovarth, G. & Kawazoe, K. (1983). Method for the calculation of effective pore size distribution in molecular sieve carbon. *Journal of Chemical Engineering of Japan*, Vol. 16,

[22] Hussain, R., Qadeer, R., Ahmad, M., & Saleem, M. (2000). X-Ray Diffraction Study of Heat-Treated Graphitized and Ungraphitized Carbon. *Turkish Journal of Chemistry*, Vol.

X-Ray

[23] IUPAC (1972). Manual of Symbols and Terminology, appendix 2, Pt.1, Colloid and Surface Chemistry. *Pure and Applied Chemistry,* Vol. 31, No. 4, (1972), pp. (578-638),

[24] IUPAC, (1997). *Compendium of Chemical Terminology*, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught & A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M.

[25] Johnson, J.E. (1959). X-ray diffraction studies of the crystallinity in polyethylene terephthalate. *Journal of Applied Polymer Science*, Vol. 2, No. 5, (September/October

[26] Langmuir I. (1918). The adsorption of gases on plane surfaces of glass, mica and platinum. *Journal of the American Chemical Society,* Vol. 40, No. 9, (September 1918), pp.

[27] Lillo-Ródenas, M.A., Cazorla-Amorós, D. & Linares-Solano, A. (2003). Understanding chemical reactions between carbons and NaOH and KOH: An insight into the chemical activation mechanism. *Carbon,* Vol. 41, No. 2, (February 2003), pp. (267-275), ISSN 0008-6223. [28] Lin, H.Y., Chen, W.C., Yuan, C.S. & Hung, C.H. (2008). Surface Functional Characteristics (C, O, S) of Waste Tire-Derived Carbon Black before and after Steam Activation. *Journal of the Air & Waste Management Association,* Vol. 58, No. 1, (1958), pp.

Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.

*Science,* Vol. 252, No. 17, (June 2006), pp. (5957–5960), ISSN 0169-4332.

(240-270), Elsevier Ltd., ISBN 978-0-08-044464-2, UK.

(1947), pp. (1351–1362), ISSN 0044-4537.

2006), pp. (6097–6101), ISSN 0169-4332.

Academic Press, ISBN 0-12-300956-1, London.

No. 6, (1983), pp. (470-475), ISSN 0021-9592.

1959), pp. (205-209), ISSN 0021-8995.

(1361–1403), ISSN 0002-7863.

(78–84). ISSN 1047-3289.

24, No. 2, (June 2000), pp. (177-83), ISSN 1300-0527.

1389), ISSN 0008-6223.

ISSN1365-3075.

#### **17. Acknowledgments**

The author thanks the support of Spanish Government (CTM2010-14883/TECNO and CTM2010-17776), Junta de Extremadura/FEDER (GRU10011), and Instituto Tecnológico de Aguascalientes (Mexico).

#### **18. References**


52 Characterization Techniques and Applications in the Wastewater Treatment

The author thanks the support of Spanish Government (CTM2010-14883/TECNO and CTM2010-17776), Junta de Extremadura/FEDER (GRU10011), and Instituto Tecnológico de

[1] Bandosz, T.J. (2009). Surface Chemistry of Carbon Materials. In *Carbon Materials for Catalysis*. Serp, P., & Figueiredo, J.L. (Eds.). pp. (58-78), Wiley, ISBN 978-0-470-17885-0. [2] Barrett, E.P., Joyner, L.G. & Halenda, P.P. (1951). The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. *Journal of the American Chemical Society*, Vol. 73, No. 1, (January 1951), pp. (373-380),

[3] Bellamy, L.J. (1986). *The infrared spectra of complex molecules*. Chapman and Hall,

[4] Biniak, S., Pakuła, M., Świątkowski, A., Bystrzejewski, M. & Błażewicz, S. (2010). Influence of high-temperature treatment of granular activated carbon on its structure and electrochemical behavior in aqueous electrolyte solution. *Journal of Material* 

[5] Boehm, H.P. (2002). Surface oxides on carbon an their analysis : a critical assessment.

[6] Bóta, A., László, K., Nagy, L.G. & Copitzky, T. (1997). Comparative study of active carbons from different precursors. *Langmuir*, Vol. 13, No. 24, (November 1997) pp.

[7] Brunauer, S., Deming, L.S.; Deming, W.S. & Teller, E. (1940). On a Theory of the van der Waals Adsorption of Gases. *Journal of the American Chemical Society*, Vol. 62, No. 7, (July

[8] Brunauer, S., Emmett, P.H. & Teller, E. (1938). Adsorption of Gases in Multimolecular Layers. *Journal of the American Chemical Society*, Vol. 60, No. 2, (February 1938), pp. (309-

[9] Burian, A., Dore, J.C., Hannon, A.C. & Honkimaki, V. (2005). Influence of hightemperature treatment of granular activated carbon. *Journal of Alloys and Compounds*,

[10] Calvino-Casilda, V., López-Peinado, A.J., Durán-Valle, C.J. & Martín-Aranda, R.M. (2010). Last Decade of Research on Activated Carbons as Catalytic Support in Chemical Processes. *Catalysis Reviews: Science and Engineering*, Vol. 52, No. 3, (2010), pp. (325–380),

[11] Chingombe, P., Saha, B. & Wakeman, R.J. (2005). Surface modification and characterisation of a coal-based activated carbon. *Carbon*, Vol. 43, No. 15, (December

[12] Cuesta, A., Dhamelincourt, P., Laureyns, J., Martínez-Alonso, A. & Tascón, J.M.D., (1994). Raman microprobe studies on carbon materials. *Carbon,* Vol. 32, No. 8, (1994),

[13] Do, D.D. (1998). *Adsorption Analysis: Equilibria and Kinetics*. Imperial College Press, ISBN

*Research*, Vol. 25, No.8, (August 2010), pp. (1617-1628), ISSN 0884-2914.

*Carbon*, Vol. 40, No. 2, (February 2002), pp. (145-149), ISSN 0008-6223.

Vol. 401, No. 1-2, (September 2005), pp. (18-23), ISSN 0925-8388.

**17. Acknowledgments**

Aguascalientes (Mexico).

ISSN 0002-7863.

ISBN 0412138506, USA.

(6502-6509), ISSN 0743-7463.

319), ISSN 0002-7863.

ISSN 0161-4940.

1940), pp. (1723-1732), ISSN 0002-7863.

2005), pp. (3132-3143), ISSN 0008-6223.

pp. (1523-1532), ISSN 0008-6223.

1-86094-130-3, London.

**18. References** 


[44] Smith, B.C. (1999). *Infrared spectral interpretation: a systematic approach*. CRC Press, ISBN

Techniques Employed in the Physicochemical Characterization of Activated Carbons 55

[45] Solum, M.S., Pugmire, R.J., Jagtoyen, M. & Derbyshire, F. (1995). Evolution of carbon structure in chemically activated wood. *Carbon*, Vol. 33, No. 9, (1995), pp. 1247-1254,

[46] Somorjai, G.A. (1994). *Introduction to Surface Chemistry and Catalysis*, Wiley Interscience,

[47] Stoeckli, H.F, Kraehenbuehl, F., & Morel, D. (1983). The adsorption of water by active carbons, in relation to the enthalpy of immersion. *Carbon*, Vol. 21, No. 6, (1983),

[48] Valente-Nabais, J.M., & Carrott, P.J.M. (2006). Chemical Characterization of Activated Carbon Fibers and Activated Carbons. *Journal of Chemical Education*, Vol. 83, No. 3,

[49] Washburn, E.W. (1921). The Dynamics of Capillary Flow. *Physical Reviews*, vol. 17,

[50] Yates, M. (2003). Área superficial, textura y distribución porosa. In: *Técnicas de análisis y caracterización de materiales.* Faraldos, M., & Goberna, C. (Eds.). pp. (221-246), CSIC,

[51] Zou, L., Huang, B., Huang, Y., Huang, Q., & Wang, Chang'an (2003). An investigation of heterogeneity of the degree of graphitization in carbon–carbon composites. *Materials Chemistry and Physics,* vol. 82, No.3, (December 2003), pp. (654–662), ISSN 0254-0584.

0-8493-2463-7, Florida.

ISBN 0471031925, UK.

(1921), pp. (273-283).

ISBN 84-00-08093-9.

pp. (589-591), ISSN 0008-6223.

(March 2006), pp. (436-438), ISSN 0021-9584.

ISSN 0008-6223.


54 Characterization Techniques and Applications in the Wastewater Treatment

[29] López, A & Márquez, C. (2003). Espectroscopía Infrarroja. In: *Técnicas de análisis y caracterización de materiales.* Faraldos, M., & Goberna, C. (Eds.). pp. (181-1859), CSIC,

[30] Lopez-Ramon, M.V., Stoeckli, F., Moreno-Castilla, C. & Carrasco-Marin, F. (1999). On the characterization of acidic and basic surface sites on carbons by various techniques.

[31] Maire, J. & Mering, J. (1970). Graphitization of soft carbons. In : *Chemistry and Physics of* 

[32] Moreno-Castilla, C. (2004). Adsorption of organic molecules from aqueous solutions on

[33] Moreno-Castilla, C., López-Ramón, M.V. & Carrasco-Marín, F. (2000). Changes in surface chemistry of activated carbons by wet oxidation. *Carbon*, Vol. 38, No. 14, (2000),

[34] Olivier, J. (1995). Modeling physical adsorption on porous and nonporous solids using density functional theory. *Journal of Porous Materials*, Vol. 2, No. 1, (June 1995), pp. (9-

[35] Pastor-Villegas, J. & Durán-Valle, C.J. (2002). Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose. *Carbon,* Vol. 40, No. 3, (March 2002), pp. (397–402), ISSN 0008-6223. [36] Pastor-Villegas, J., Durán-Valle, C.J., Valenzuela-Calahorro, C. & Gómez-Serrano, V. (1998). Organic chemical structure and structural shrinkage of chars prepared from rockrose. *Carbon*, Vol. 36, No. 9, (September 1998), pp. (1251–1256), ISSN 0008-6223. [37] Pastor-Villegas, J., Gómez-Serrano, V., Durán-Valle, C.J. & Higes-Rolando, F.J. (1999). Chemical study of extracted rockrose and of chars and activated carbons prepared at different temperatures. *Journal of Analytical and Applied Pyrolysis,* Vol. 50, No. 1, (April

[38] Pradhan, B.K. & Sandle, N.K. (1999). Effect of different oxidizing agent treatments on the surface properties of activated carbons. *Carbon*, Vol. 37, No. 8, (January 1999), pp.

[39] Raymundo-Piñero, E., Cazorla-Amorós, D., Linares-Solano, A., Find, J., Wild, U. & Schlögl, R. Structural characterization of N-containing activated carbon fibers prepared from a low softening point petroleum pitch and a melamine resin. *Carbon,* Vol. 40, No.

[40] Rubio-Montero, M.P., Durán-Valle, C.J., Jurado-Vargas, M., & Botet-Jiménez, A. (2009). Radioactive content of charcoal. *Applied Radiation and Isotopes*, Vol. 67, No. 5, (May

[41] Scheele, C.W. (1780). *Chemical Observations and Experiments on Air and Fire*. J. Johnson,

[42] Shen, W., Li, Z., & Liu, Y. (2008). Surface Chemical Functional Groups Modification of Porous Carbon. *Recent Patents on Chemical Engineering*, Vol. 1, No. 1, (January 2008), pp.

[43] Sing, K.S.W., Everett, D.H., Haul, R.A.W., et al. (1985). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). *Pure and Applied Chemistry*, Vol. 57, No. 4, (1985), pp.

*Carbon*, Vol. 37, No. 8, (January 1999), pp. (1215-1221), ISSN 0008-6223.

*Carbon*. Walker, P.L. (ed.). pp. (125-189), Marcel Dekker, ISSN 0069-3138.

carbon materials. *Carbon*, Vol. 42, No. 1, (2004), pp. (83-94), ISSN 0008-6223.

ISBN 84-00-08093-9.

17), ISSN 1380-2224.

pp. (1995-2001), ISSN 0008-6223.

1999), pp. (1–16), ISSN 0165-2370.

4, (April 2002), pp. (597-608), ISSN 0008-6223.

2009), pp. (953–956), ISSN 0969-8043.

ISBN 9781171413929, London.

(27-40), ISSN 2211-3347.

(603-619), ISSN 1365-3075.

(1323-1332), ISSN 0008-6223.


**4** 

*México* 

**Applications of Activated Carbons** 

**for the Wastewater Treatment** 

*Instituto Tecnológico de Aguascalientes* 

**Obtained from Lignocellulosic Materials** 

Activated carbons are used in a number of industrial applications including separation and purification technologies, catalytic processes, biomedical engineering, and energy storage, among others. The extensive application of activated carbon is mainly due to its relatively lowcost with respect to other adsorbents, wide availability, high performance in adsorption processes, surface reactivity and the versatility to modify its physical and chemical properties for synthesizing adsorbents with very specific characteristics (Haro et al., 2011). In particular, the adsorption on activated carbon is the most used method for wastewater treatment because it is considered a low-cost purification process where trace amounts of several pollutants can be effectively removed from aqueous solution. Recently, the demand of activated carbons has increased significantly as a water-purifying agent to reduce the environmental risks caused by

Traditionally, the activated carbons used in wastewater treatment are obtained from coal/lignite, wood or animal bones but, recently, there is a growing interest in the use of alternative and low-cost precursors for their production (Altenor et al., 2009; Elizalde-González & Hernández-Montoya, 2007; Mohamed et al., 2010). Specifically, lignocellulosic wastes are a low-cost natural carbon source for the synthesis of several materials including the production of activated carbons. In this context, it is convenient to remark that natural resources play a dominant role in the economic activities and the utilization of lignocellulosic wastes for the synthesis of valuable commercial products may contribute to the economic development and to prevent environment pollution especially in developing countries (Satyanarayana et al., 2007). Therefore, lignocellulosic materials are considered as an interesting and important natural resource for production of activated carbons based on the fact that several billion tons of these materials are available (Mohamed et al., 2010; Satyanarayana et al., 2007). Actually, these precursors are considered as the most appropriate candidates for a cost-effective preparation of activated carbons (Silvestre-Albero

the water pollution worldwide (Altenor et al., 2009; Bello-Huitle et al., 2010).

**1. Introduction** 

et al., 2012).

Ma. del Rosario Moreno-Virgen, Rigoberto Tovar-Gómez, Didilia I. Mendoza-Castillo and Adrián Bonilla-Petriciolet
