Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids

*Huei Ruey Ong, Wan Mohd Eqhwan Iskandar and Md. Maksudur Rahman Khan*

#### **Abstract**

The fast development in the extraction technique of silica from biomass has resulted in the signification use of silica in the industry. Rice is one of the world's most significant plants, which serve as a carbohydrate intake for humans. Rice husk is one of the main agro-wastes comprising big quantities of silicate. This chapter presenting the review on rice husk nanosilica production techniques by thermal and chemical methods. A direction on efficient and sustainable nanosilica extraction method will be discussed. Apart from that, method on nanofluids preparation will be accumulated with respect to the end application. Moreover, the influence of nanoparticle in nanofluids in terms of heat conductivity, rheological properties, and stability will be discussed. The potential application area of silica nanofluids such as solar, automobile, electronic cooling, and biomedical application will be explored.

**Keywords:** rice husk nanosilica, chemical method, thermal method, industrial application

#### **1. Introduction**

The surface area and porosity of the nanosilica are large and can be commonly used in products such as fillers [1], pharmaceuticals [2], catalysts [3], and chromatography [4]. Industrial silica production uses sodium silicate as the main ingredient of silicone. Nevertheless, a large amount of energy is required to produce sodium silicate via melting the quartz sand and sodium carbonate at 1300°C [5]. In the future, fossil fuel energy may not be viable. Thus, it is also fascinating to create a technique for producing nanosilica from a silicon-containing biomass content that will be economically feasible. Biomass is a significant resource for renewable energy and represents 15% of the worldwide power supply [6]. Rice husk (RH) is one type of biomass, which is effective heat deliver and lignocellulose rich for biological oils [7]. The global annual product of RH is about 100 million tons [8]. RH is rich in silica content (~20 wt%) and abundant in rice milling as waste. RH is not widely known due to lack of commercial utilization. Nanosilica precursor is an exciting future application for the preparation of advanced materials, such as carbon/silica composites [9], photocatalysts [10], hydrogen production as well as CO2 capture materials [11, 12], and metal ion removal adsorbents [13]. Nanosilica with porous RH composition can be prepared by various methods [14–16].

Kalapathy et al. [17] explored sodium hydroxide dissolved xerogel formation utilizing RH as raw resources. They discovered that combining the rice husk ash (RHA) acid with xerogel's washing step can efficiently improve nanosilica sample purity. Following a pre-treatment with acid, Zhang et al. [18] utilized RH as a forerunner to acquire superfine 30–200 nm diameter nanosilica the pretreated sample. In the latest studies, biotransformed nanosilica with *Fusarium oxysporum* fungus [19] or via a bio-digestion process using worms [20]. Witoon et al. [21] utilized RHA as raw resources for the preparation of bimodal porous nanosilica and Chitosan as a template.

Meanwhile, nanofluid is comprised of nanometer-sized particles (nanoparticles) and fluids. Water, engine oil, ethylene glycol, and so on are usually used for base fluids in many industries including transport, power supply, manufacturing, and electronics [22]. Conventional base fluids suffer from low heat transfer performance, which limits its application [23]. In order to overcome the drawbacks, nanosized particles suspended in the base fluid can improve the transfer of heat and rheological properties, acting as property enhancer [24]. Moreover, most of the nanofluid studies underline the nanoparticle preparation methodology. A research from Rao et al. [25] found that nanofluids have greater thermal conductivity than conventional fluids, strongly nonlinear temperature dependence on effective thermal conductivity, improve or decrease heat transfer in single-phase flow, improve or decrease nucleate pool boiling heat transfer, and yield higher critical heat flows under pool boiling conditions. To the best of our knowledge, RH-derived nanosilica has not been reported elsewhere. In this context, the method of preparing nanosilica will be deliberated. Moreover, the method of nanofluid preparation from nanoparticle and the potential applications of nanofluids will be discussed.

#### **2. Method of preparing nanosilica**

Thermal and chemical methods are the two major methods that have been widely adopted for silica production from biomass. **Figure 1** illustrated the methods used for producing nanosilica from biomass/agricultural waste.

#### **2.1 Thermal methods**

Thermal methods involve the utilization of furnace muffles, fixed bed furnace, fluidized bed reactor, and other thermal methods that consist of inclined step-grate furnace, cyclone furnace, and rotary kiln. The thermal technology does have a number of disadvantages such as required more time for reaction, hot spot formation, the absence of free-flowing air for full carbon oxidation, and many others [26].

#### *2.1.1 Electric/muffle furnace*

Nanosilica is extracted from agricultural waste in a laboratory scale by electric/ muffle furnace. The biggest disadvantage in using this technology is the long reaction time and a lower production rate. Patil et al. [27] investigated the biggest RH nanosilica extraction, consisting in thermal treatment with electric oven for 6 hours at 700°C at different temperatures. XRD and FTIR were used to characterize the sample. XRD information showed that the nanosilica acquired was amorphous in nature. About 95.55% pure nanosilica obtained from RHA with acid leaching preceded by the treatment of thermal heating with muffle oven at 600°C [28]. According to Bogeshwaran et al. [29], silica extracted from RH is highly

**63**

**Figure 1.**

ture and time required [34].

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

pozzolanic when burned in the muffle furnace. By thermal treatment, Chen et al. [30] utilized wheat straw to effectively produce nanosilica products. The combustion of wheat straw ash was kept at 500°C for 8 hours. The collected sample was washed with distilled water after the combustion and followed by calcination at the temperature from 400 to 700°C in a muffle furnace. Nano-amorphous silica was characterized by using XRD, TEM, EDX, FTIR, and BET. Ahmad Alyosef et al. [31] investigated the use of thermo-chemical treatment for meso/macroporous biogenic silica (3–1500 nm) from biomass such as miscanthus, wheat straw, and cereal remnant pellets. The biomass (wheat straw) was leached by concentrated H2SO4 (5 M). The wheat straw proportion of H2SO4 was controlled at 1:10 (gmL<sup>−</sup><sup>1</sup>

*Various treatments used to produce nanosilica from agricultural waste.*

The treatment was performed under continuous stirring (1000 rpm) at 353 K for 24 hours. The ash of silica generated at various temperatures and times after heating by furnace. The combustion and acid leaching therapy of RH obtained pure amorphous silica. HCl, H2SO4, and HNO3 leached the husk with different concentrations. The wheat-husk ash samples were positioned inside the muffle furnace at the temperature from 300 to 700°C for 24 hour after leaching treatment. The research proves that hydrochloric acid leaching treatment was more effective than any other acid to remove metal ions. Pure amorphous silica from acid-treated wheat husk ash was obtained at 500–700°C [32]. Yalcin and Sevinc [33] manufactured amorphous silica RH successfully at 600°C in a tubular stainless steel reactor for 4 hours in an electronic laboratory muffle furnace. In particular, electric/ muffle furnace can increase the purity of silica contents obtained from incineration. Except that, amorphous silica structure can be obtained by incineration up to 425°C for 90 minutes. The structure of silica varies on the incineration tempera-

).

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

#### *Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

**Figure 1.**

*Engineered Nanomaterials - Health and Safety*

**2. Method of preparing nanosilica**

**2.1 Thermal methods**

*2.1.1 Electric/muffle furnace*

template.

Kalapathy et al. [17] explored sodium hydroxide dissolved xerogel formation utilizing RH as raw resources. They discovered that combining the rice husk ash (RHA) acid with xerogel's washing step can efficiently improve nanosilica sample purity. Following a pre-treatment with acid, Zhang et al. [18] utilized RH as a forerunner to acquire superfine 30–200 nm diameter nanosilica the pretreated sample. In the latest studies, biotransformed nanosilica with *Fusarium oxysporum* fungus [19] or via a bio-digestion process using worms [20]. Witoon et al. [21] utilized RHA as raw resources for the preparation of bimodal porous nanosilica and Chitosan as a

Meanwhile, nanofluid is comprised of nanometer-sized particles (nanoparticles) and fluids. Water, engine oil, ethylene glycol, and so on are usually used for base fluids in many industries including transport, power supply, manufacturing, and electronics [22]. Conventional base fluids suffer from low heat transfer performance, which limits its application [23]. In order to overcome the drawbacks, nanosized particles suspended in the base fluid can improve the transfer of heat and rheological properties, acting as property enhancer [24]. Moreover, most of the nanofluid studies underline the nanoparticle preparation methodology. A research from Rao et al. [25] found that nanofluids have greater thermal conductivity than conventional fluids, strongly nonlinear temperature dependence on effective thermal conductivity, improve or decrease heat transfer in single-phase flow, improve or decrease nucleate pool boiling heat transfer, and yield higher critical heat flows under pool boiling conditions. To the best of our knowledge, RH-derived nanosilica has not been reported elsewhere. In this context, the method of preparing nanosilica will be deliberated. Moreover, the method of nanofluid preparation from

nanoparticle and the potential applications of nanofluids will be discussed.

used for producing nanosilica from biomass/agricultural waste.

Thermal and chemical methods are the two major methods that have been widely adopted for silica production from biomass. **Figure 1** illustrated the methods

Thermal methods involve the utilization of furnace muffles, fixed bed furnace, fluidized bed reactor, and other thermal methods that consist of inclined step-grate furnace, cyclone furnace, and rotary kiln. The thermal technology does have a number of disadvantages such as required more time for reaction, hot spot formation, the absence of free-flowing air for full carbon oxidation, and many others [26].

Nanosilica is extracted from agricultural waste in a laboratory scale by electric/

muffle furnace. The biggest disadvantage in using this technology is the long reaction time and a lower production rate. Patil et al. [27] investigated the biggest RH nanosilica extraction, consisting in thermal treatment with electric oven for 6 hours at 700°C at different temperatures. XRD and FTIR were used to characterize the sample. XRD information showed that the nanosilica acquired was amorphous in nature. About 95.55% pure nanosilica obtained from RHA with acid leaching preceded by the treatment of thermal heating with muffle oven at 600°C [28]. According to Bogeshwaran et al. [29], silica extracted from RH is highly

**62**

*Various treatments used to produce nanosilica from agricultural waste.*

pozzolanic when burned in the muffle furnace. By thermal treatment, Chen et al. [30] utilized wheat straw to effectively produce nanosilica products. The combustion of wheat straw ash was kept at 500°C for 8 hours. The collected sample was washed with distilled water after the combustion and followed by calcination at the temperature from 400 to 700°C in a muffle furnace. Nano-amorphous silica was characterized by using XRD, TEM, EDX, FTIR, and BET. Ahmad Alyosef et al. [31] investigated the use of thermo-chemical treatment for meso/macroporous biogenic silica (3–1500 nm) from biomass such as miscanthus, wheat straw, and cereal remnant pellets. The biomass (wheat straw) was leached by concentrated H2SO4 (5 M). The wheat straw proportion of H2SO4 was controlled at 1:10 (gmL<sup>−</sup><sup>1</sup> ). The treatment was performed under continuous stirring (1000 rpm) at 353 K for 24 hours. The ash of silica generated at various temperatures and times after heating by furnace. The combustion and acid leaching therapy of RH obtained pure amorphous silica. HCl, H2SO4, and HNO3 leached the husk with different concentrations. The wheat-husk ash samples were positioned inside the muffle furnace at the temperature from 300 to 700°C for 24 hour after leaching treatment. The research proves that hydrochloric acid leaching treatment was more effective than any other acid to remove metal ions. Pure amorphous silica from acid-treated wheat husk ash was obtained at 500–700°C [32]. Yalcin and Sevinc [33] manufactured amorphous silica RH successfully at 600°C in a tubular stainless steel reactor for 4 hours in an electronic laboratory muffle furnace. In particular, electric/ muffle furnace can increase the purity of silica contents obtained from incineration. Except that, amorphous silica structure can be obtained by incineration up to 425°C for 90 minutes. The structure of silica varies on the incineration temperature and time required [34].

#### *2.1.2 Fixed bed furnace*

The manufacturing of RH silica was also carried out using a fixed bed furnace. By using fixed bed furnace, Yang et al. [35] obtained amorphous silica in burst nano size. In this process, RH treated with raw and acid was conducted in fixed bed furnace for pyrolysis at 600–1200°C. The amorphous silica transforms into crystalline at 1000°C. Hamad [36] discovered RHA silica successfully using the 500–1150°C muffle furnace and fixed bed reactor.

#### *2.1.3 Fluidized bed reactor*

The advantages of fluidized bed reactor are the distribution of uniform temperature, fast reaction time, efficiency of carbon conversion, low temperature operating range, high intensity of combustion, elevated reaction of gas-solid mixtures, and outstanding mixing characteristics [37, 38]. Huang et al. [39] manufactured RH silica white by utilizing fluidized bed reactor. RH amorphous silica can be obtained by using fluidized bed bubbling pilot plants at different temperatures and at different speeds [40]. Genieva et al. [41] obtained RH silica material that is produced by the rice-milling phase, and it is a large agricultural waste product by using and characterizing the fluidized bed reactor throughout the nitrogen atmosphere. Luan and Chou [42] found RH silica in a modified fluidized bed reactor throughout the existence of pilot flame. Therefore, outcome revealed that the high-activity silica product was acquired.

#### *2.1.4 Other thermal method*

Inclined step-grate furnace is commonly used in the manufacturing of RHA. It consists of feeding component, chamber of combustion, and chamber of ash precipitation. The disadvantage of using this RHA manufacturing methodology is low yield quality and elevated unburnt carbon content. RH was provided from the upper part of the reactor as air flows from the lower part [43]. Moreover, cyclonic furnace was developed by Singh et al. [44]. In this furnace, the air kept the husk spinning and accelerated the combustion in the chamber. The benefit of using cyclone furnace to make husk ash is that the product has less carbon content. Subsequently, rotating kiln is a pyro-processing tool used in the ongoing process to increase calcination materials. Sugita [45] patented active RHA generated from rotary kiln. In this process, RH has been carbonized by an upstream rotary kiln that is heated at 300–400°C by electric heaters, burners, or other heat sources. Carbonized RH is supplied into rotating oven and burnt at 600°C after carbonization. These techniques effectively produced the husk ash. The disadvantage of using this technique was the need for additional fuel to avoid ash from being crystallized, longer reaction time, and high energy required.

#### *2.1.5 Discussion on thermal method*

Thermal method is one of the initial initiatives to obtain silica nanoparticle derived from RH biomass (**Table 1**). Muffle furnace helps in incineration of RHA to form nanosilica. The crystalline of nanosilica is dependent on the temperature and before incineration process takes place. Utilizing temperature around 500–700°C will form amorphous nanosilica. Alternatively, crystalline structure of nanosilica obtains above temperature of 900°C [46]. Chemical pre-treatment is vital to avoid any unburned material that leads to reduce the nanosilica's purity. Fixed bed furnace has an ideal temperature of 600–700°C to obtain white RHA. Complete combustion

**65**

**Electric/muffle furnace**

**No**

1 2 3

Furnace in which the

RH RH

500°C

8 hours

700°C

6 hours

—

—

3–1500 nm

—

—

95.55%

—

Patil et al. [27]

Chen et al. [30]

subject material is

isolated from the fuel

and all of the products

RH

80

24 hours

of combustion,

including gases and

flying ash

**Fixed bed furnace**

1

Material is heaped onto

RH

600–

—

1–10 nm

—

—

Yang et al. [35]

1200°C

a grate, and preheated

primary air (called

RH

500–1150°C

—

—

—

—

Hamad [36]

under fire air) is blown

from under the bed to

burn the fixed carbon

**Fluidized bed reactor**

1

A simple fluidized

RH

800–950°C

4–8 hours

—

92–96%

—

Pitt [37] and Soltani et al.

[38]

Genieva et al. [41]

Luan and Chou [42]

reactor consists of a

room, which is assisted

RH

100°C

4 hours

20 nm

—

—

2 3 **Table 1.** *List of thermal method and its parameters.*

by a distributor plate,

and contains a bed of

RH

60–860°C

4 hours

—

—

—

inert particles like sand

**Method**

**Material**

**Time**

**Temperature (after getting silica gel)**

**Size**

**Purity**

**Yield**

**References**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

Ahmad Alyosef et al. [31]


#### *Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

*Engineered Nanomaterials - Health and Safety*

muffle furnace and fixed bed reactor.

The manufacturing of RH silica was also carried out using a fixed bed furnace. By using fixed bed furnace, Yang et al. [35] obtained amorphous silica in burst nano size. In this process, RH treated with raw and acid was conducted in fixed bed furnace for pyrolysis at 600–1200°C. The amorphous silica transforms into crystalline at 1000°C. Hamad [36] discovered RHA silica successfully using the 500–1150°C

The advantages of fluidized bed reactor are the distribution of uniform temperature, fast reaction time, efficiency of carbon conversion, low temperature operating range, high intensity of combustion, elevated reaction of gas-solid mixtures, and outstanding mixing characteristics [37, 38]. Huang et al. [39] manufactured RH silica white by utilizing fluidized bed reactor. RH amorphous silica can be obtained by using fluidized bed bubbling pilot plants at different temperatures and at different speeds [40]. Genieva et al. [41] obtained RH silica material that is produced by the rice-milling phase, and it is a large agricultural waste product by using and characterizing the fluidized bed reactor throughout the nitrogen atmosphere. Luan and Chou [42] found RH silica in a modified fluidized bed reactor throughout the existence of pilot flame. Therefore, outcome revealed that the high-activity silica

Inclined step-grate furnace is commonly used in the manufacturing of RHA. It

consists of feeding component, chamber of combustion, and chamber of ash precipitation. The disadvantage of using this RHA manufacturing methodology is low yield quality and elevated unburnt carbon content. RH was provided from the upper part of the reactor as air flows from the lower part [43]. Moreover, cyclonic furnace was developed by Singh et al. [44]. In this furnace, the air kept the husk spinning and accelerated the combustion in the chamber. The benefit of using cyclone furnace to make husk ash is that the product has less carbon content. Subsequently, rotating kiln is a pyro-processing tool used in the ongoing process to increase calcination materials. Sugita [45] patented active RHA generated from rotary kiln. In this process, RH has been carbonized by an upstream rotary kiln that is heated at 300–400°C by electric heaters, burners, or other heat sources. Carbonized RH is supplied into rotating oven and burnt at 600°C after carbonization. These techniques effectively produced the husk ash. The disadvantage of using this technique was the need for additional fuel to avoid ash from being crystallized,

Thermal method is one of the initial initiatives to obtain silica nanoparticle derived from RH biomass (**Table 1**). Muffle furnace helps in incineration of RHA to form nanosilica. The crystalline of nanosilica is dependent on the temperature and before incineration process takes place. Utilizing temperature around 500–700°C will form amorphous nanosilica. Alternatively, crystalline structure of nanosilica obtains above temperature of 900°C [46]. Chemical pre-treatment is vital to avoid any unburned material that leads to reduce the nanosilica's purity. Fixed bed furnace has an ideal temperature of 600–700°C to obtain white RHA. Complete combustion

*2.1.2 Fixed bed furnace*

*2.1.3 Fluidized bed reactor*

product was acquired.

*2.1.4 Other thermal method*

longer reaction time, and high energy required.

*2.1.5 Discussion on thermal method*

**64**

**Table 1.** *List of thermal method and its parameters.* of carbon content is the major benefit of this furnace. However, the heat loss during the process could affect the temperature, which leads to unstable production of silica structure [36]. Fluidized bed reactor has many benefits such as high combustion intensity, lower operating temperature range, simple operation and quick start-up, and easier ash removal. However, it appears hard to fluidize RH and husk char or otherwise blended with sand, mold, and ash to produce a multi-structure [47–49]. Inclined step grate furnace is simple in construction and process, but it is inefficient in combustion and separation of ash resulted smoke and spark partially drawing into the dryer plenum [43]. The rotary kiln carbonizes RH first by burning without flaming and transforms the carbonized RH into ash. This method easily produces white RHA, which has excellent chemical reactivity [45]. This furnace requires new improvement to the capacity part due to low production along the process. Soponronnarit et al. [50] prove that cyclone furnace able to increase the furnace efficiency by 16% rises the air by 90%. Observation made proves that the height of ash on the grate does not affect the efficiency of the furnace. However, incomplete combustion may occur because of too high airflow rate in tertiary duct that did not support combustion since the burning RH fell quickly from the grate. Among them, fluidized bed reactor suites the best requirement for producing silica due to its better purity (92–96%) and operating at optimum temperature (800–950°C), which is also in agreement with Soltani et al. [38].

#### **2.2 Chemical method**

Chemical techniques include techniques of alkaline extraction used to achieve pure and high silica quantities. However, this method is costly due to a slightly longer reaction time (24–48 hours) and involves different measures with the use of different sorts of chemicals. Usually, RH will go through thermal process (incineration) to obtain RHA before proceeding to any chemical process involvement.

#### *2.2.1 Alkaline extraction*

Alkaline extraction and acid neutralization are an effective and easy technique of extracting amorphous silica from agricultural waste. Zulkifli et al. [51] utilized alkali extraction technique from RH to extract silica particles in order to remove metallic impurities. In a water bath, RHA was initially treated with HCl for 4 hours at 75°C. The filtration took place by constantly washing using distilled water until neutral state was reached and dried at 110°C for 12 hours. The NaOH was used to prepare a constantly stirring solution of sodium silicate for 1 hours at 90°C. The silicate sodium solution was then reacted to ethanol, and a steady 10-minute water mix was added. The whole mixture has been titrated 3 M H3PO4 until gel formation is carried out. The product after centrifugation of yellowish gel was washed with distilled water to clear away residual sodium silicate and phosphate, followed by calcination to produce silica nanoparticles. Hassan et al. [52] prepared nanosilica from rice husk in high surface area using the NaOH (alkaline extraction method). In their study, analyses of characterization of nanosilica were investigated by using FTIR, XRD, SEM, and TEM. The impact from their study states that more than 95% of nanosilica obtained. Liou and Yang [53] investigated various variables of silica derived from RHA processing via the alkali-extracted method. Acid and alkaline concentrations, gelation pH, aging time, and temperature have been optimized to prepare SiO2 nanoparticles from RHA. The effects on the surface area from various acids and silica particle size have also been assessed. Rehman et al. [54] synthesized nanosilica using silica source from RHA. Silica nanoparticles were obtained from RH through the use of NaOH alkaline sol-gel method.

**67**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

The application of H2SO4/water/butanol to pH 4 precipitated the silica. Thuc and Thuc's [55] technique was used to obtain nanosilica particles with high-specific surface area. Their study continues to prepare zeolite Y in sodium form (NaY) derived from nanosilica. Awizar et al. [56] produced and used nanosilica as a green corrosion inhibitor by alkaline extraction. Haq et al. [57] obtained RHA silica with reflux condition for a varying period of time by NaOH solution. The RHA reaction

SiO2 + 2 NaOH → Na2SiO3 + H2O (white ash) (sodium hydroxide) (sodium silicate) (water)

Na2SiO3 + HCl → SiO2 + NaCl + H2O

Low surface microsphere silica can be achieved by alkaline and acid precipitation from wheat husk ash. Nano amorphous silica with a specific surface area of

/g was achieved after alkaline extraction with NaOH [58]. Masnar and Coorey [59] prepared silica nanoparticles by following the same step as Liou and Yang [53]. Silica nanoparticles obtained at 80°C for 48 hours after solids have been

Selvakumar et al. [60] prepared silica from RHA by adopting pre-treatment process (acid process). Pre-treatment of acid was used to enhance the silica purity with the effective removal of the majority of metallic impurities and to produce silica (white color). From their study, RHA was pre-treatment by various acids (pH 1, 3, 5, or 7 using 6 N hydrochloric acid, nitric acid, and sulfuric acid). RHA amorphous nanostructured silica was produced using alkaline extraction technique with NaOH solutions (2.0–3.0 N). Their research showed that treatment with 2.5 N NaOH produced RHA containing 90.44% silica. Rungrodnimitchai, Phokhanusai, and Sungkhaho [61] prepared RHA silicate materials using 2.0 M of sodium hydroxide with the help of microwave (800 W) for 10 minutes. Zhang et al. [62] synthesized silica nanoparticles from RHA by involving acid pre-treatment. Na2CO3 solution was added after the pre-treatment to obtain nanosilica slurry. The precipitation was then cleaned with distilled water and dried for 24 hours in the vacuum oven at 120°C. Adam et al. [63] obtained spherical nano size silica from RH by using nitric acid (65%) and sodium hydroxide. No calcination for ash formation was required in

Faizul et al. [64] prepared amorphous nanosilica with the size of 181.2 nm with mild acid solution (citric acid, acetic acid, and phosphoric acid) obtained from rice husk. Carmona et al. [65] used acid leaching to synthesize nanosilica of two kinds of rice husk, namely the agulhinha and the catetus. They believe that their method can be efficient in removing impurities (Zn, MN, Ca, K, Mg, Cu, and Al). Mahmud et al. [66] used hydrochloric acid for acid leaching to obtain high purity and high surface area of nanosilica. Rafiee and Shahebrahimi [67] prepared nanosilica from rice husk with high surface area by acid leaching treatment. The average size of nanosilica is 6–7 nm supported by the catalyst. Bakar et al. [68] prepared high purity silica by acid treatment followed by combustion. Pre-combustion rice husk

form)

(sodium chloride)

(water)

Silica was precipitated by sodium silicate acid neutralization [55].

(hydrochloric acid) (silica gel

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

(sodium silicate)

8.23 m2

dried.

this treatment.

*2.2.2 Acid extraction*

mechanism mixed with NaOH was given as follows:

#### *Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

The application of H2SO4/water/butanol to pH 4 precipitated the silica. Thuc and Thuc's [55] technique was used to obtain nanosilica particles with high-specific surface area. Their study continues to prepare zeolite Y in sodium form (NaY) derived from nanosilica. Awizar et al. [56] produced and used nanosilica as a green corrosion inhibitor by alkaline extraction. Haq et al. [57] obtained RHA silica with reflux condition for a varying period of time by NaOH solution. The RHA reaction mechanism mixed with NaOH was given as follows:


Silica was precipitated by sodium silicate acid neutralization [55].


Low surface microsphere silica can be achieved by alkaline and acid precipitation from wheat husk ash. Nano amorphous silica with a specific surface area of 8.23 m2 /g was achieved after alkaline extraction with NaOH [58]. Masnar and Coorey [59] prepared silica nanoparticles by following the same step as Liou and Yang [53]. Silica nanoparticles obtained at 80°C for 48 hours after solids have been dried.

Selvakumar et al. [60] prepared silica from RHA by adopting pre-treatment process (acid process). Pre-treatment of acid was used to enhance the silica purity with the effective removal of the majority of metallic impurities and to produce silica (white color). From their study, RHA was pre-treatment by various acids (pH 1, 3, 5, or 7 using 6 N hydrochloric acid, nitric acid, and sulfuric acid). RHA amorphous nanostructured silica was produced using alkaline extraction technique with NaOH solutions (2.0–3.0 N). Their research showed that treatment with 2.5 N NaOH produced RHA containing 90.44% silica. Rungrodnimitchai, Phokhanusai, and Sungkhaho [61] prepared RHA silicate materials using 2.0 M of sodium hydroxide with the help of microwave (800 W) for 10 minutes. Zhang et al. [62] synthesized silica nanoparticles from RHA by involving acid pre-treatment. Na2CO3 solution was added after the pre-treatment to obtain nanosilica slurry. The precipitation was then cleaned with distilled water and dried for 24 hours in the vacuum oven at 120°C. Adam et al. [63] obtained spherical nano size silica from RH by using nitric acid (65%) and sodium hydroxide. No calcination for ash formation was required in this treatment.

#### *2.2.2 Acid extraction*

Faizul et al. [64] prepared amorphous nanosilica with the size of 181.2 nm with mild acid solution (citric acid, acetic acid, and phosphoric acid) obtained from rice husk. Carmona et al. [65] used acid leaching to synthesize nanosilica of two kinds of rice husk, namely the agulhinha and the catetus. They believe that their method can be efficient in removing impurities (Zn, MN, Ca, K, Mg, Cu, and Al). Mahmud et al. [66] used hydrochloric acid for acid leaching to obtain high purity and high surface area of nanosilica. Rafiee and Shahebrahimi [67] prepared nanosilica from rice husk with high surface area by acid leaching treatment. The average size of nanosilica is 6–7 nm supported by the catalyst. Bakar et al. [68] prepared high purity silica by acid treatment followed by combustion. Pre-combustion rice husk

*Engineered Nanomaterials - Health and Safety*

also in agreement with Soltani et al. [38].

**2.2 Chemical method**

*2.2.1 Alkaline extraction*

of carbon content is the major benefit of this furnace. However, the heat loss during the process could affect the temperature, which leads to unstable production of silica structure [36]. Fluidized bed reactor has many benefits such as high combustion intensity, lower operating temperature range, simple operation and quick start-up, and easier ash removal. However, it appears hard to fluidize RH and husk char or otherwise blended with sand, mold, and ash to produce a multi-structure [47–49]. Inclined step grate furnace is simple in construction and process, but it is inefficient in combustion and separation of ash resulted smoke and spark partially drawing into the dryer plenum [43]. The rotary kiln carbonizes RH first by burning without flaming and transforms the carbonized RH into ash. This method easily produces white RHA, which has excellent chemical reactivity [45]. This furnace requires new improvement to the capacity part due to low production along the process. Soponronnarit et al. [50] prove that cyclone furnace able to increase the furnace efficiency by 16% rises the air by 90%. Observation made proves that the height of ash on the grate does not affect the efficiency of the furnace. However, incomplete combustion may occur because of too high airflow rate in tertiary duct that did not support combustion since the burning RH fell quickly from the grate. Among them, fluidized bed reactor suites the best requirement for producing silica due to its better purity (92–96%) and operating at optimum temperature (800–950°C), which is

Chemical techniques include techniques of alkaline extraction used to achieve pure and high silica quantities. However, this method is costly due to a slightly longer reaction time (24–48 hours) and involves different measures with the use of different sorts of chemicals. Usually, RH will go through thermal process (incineration) to obtain RHA before proceeding to any chemical process involvement.

Alkaline extraction and acid neutralization are an effective and easy technique of extracting amorphous silica from agricultural waste. Zulkifli et al. [51] utilized alkali extraction technique from RH to extract silica particles in order to remove metallic impurities. In a water bath, RHA was initially treated with HCl for 4 hours at 75°C. The filtration took place by constantly washing using distilled water until neutral state was reached and dried at 110°C for 12 hours. The NaOH was used to prepare a constantly stirring solution of sodium silicate for 1 hours at 90°C. The silicate sodium solution was then reacted to ethanol, and a steady 10-minute water mix was added. The whole mixture has been titrated 3 M H3PO4 until gel formation is carried out. The product after centrifugation of yellowish gel was washed with distilled water to clear away residual sodium silicate and phosphate, followed by calcination to produce silica nanoparticles. Hassan et al. [52] prepared nanosilica from rice husk in high surface area using the NaOH (alkaline extraction method). In their study, analyses of characterization of nanosilica were investigated by using FTIR, XRD, SEM, and TEM. The impact from their study states that more than 95% of nanosilica obtained. Liou and Yang [53] investigated various variables of silica derived from RHA processing via the alkali-extracted method. Acid and alkaline concentrations, gelation pH, aging time, and temperature have been optimized to prepare SiO2 nanoparticles from RHA. The effects on the surface area from various acids and silica particle size have also been assessed. Rehman et al. [54] synthesized nanosilica using silica source from RHA. Silica nanoparticles were obtained from RH through the use of NaOH alkaline sol-gel method.

**66**

was leached with hydrochloric acid and sulfuric acid to achieve pure silica. Thus, XRF confirmed the purity of amorphous silica over 99%.

#### *2.2.3 Other chemical extraction methods of silica from agricultural waste*

Many chemical treatments exist for the production of silica from bio-waste. Faizul et al. [69] obtained amorphous silica and activated carbon by three effective procedures by using toluene/ethanol, NaClO2, and KOH. The method of calcination was used in the production of nano amorphous silica (100–120 nm). The manufacturing of amorphous silica was carried out using organic acid leaching instead of strong acid [70]. Ionic liquid was also used in the manufacturing of silica from agricultural waste by Kumar et al. [71].

#### *2.2.4 Discussion on chemical method*

Chemical method is advisable to obtain high purity of amorphous nanosilica due to its effective chemical reaction (**Tables 2** and **3**). Basically, there are two types of extraction methods (alkaline extraction and acid extraction). In this review, alkaline extraction method is predominantly compared to acid extraction method in terms of nanosilica properties obtained. Hassan et al. [52] produced the preparation of silica nanoparticle by alkali treatment and obtained more than 95% purity of nanosilica. Furthermore, Liou and Yang [53] prepared nanosilica and obtained 99.48% of silica content throughout alkali treatment. For further improvement, Selvakumar et al. [60] used pre-treatment and result in high purity (85%) of silica contents. Similarly, Adam et al. [63] also reported acid pre-treatment before conventional alkaline method, where ~95% purity of nanosilica was obtained. As for pre-treatment is use to enhance silica purity and remove metallic impurities. Meanwhile, Rungrodnimitchai et al. [61] used 2.0 M sodium hydroxide assisted by microwave (800 W) to obtain high purity of nanosilica from RHA. The modification could enhance the properties of the nanosilica obtained from the conventional method in terms of morphology, size, and purities as presented in **Table 2**. Furthermore, acid leaching method has been presented in **Table 3**. It was found that acid leaching method produced high purity of nanosilica as reported by Bakar et al. [68], where 99% purity of nanosilica was obtained with 500–700 nm. Similarly, Mahmud et al. [66] also reported that acid leaching method produced 99% high purity of nanosilica using HCl. Referring to above, acid leaching improves the other metal removal and increases the purity of nanosilica. It is noticed that single method like alkaline extraction and acid leaching method required high temperature thermal process to acquire nanosized silica. While combination of acid leaching and alkaline method could provide high purity of nanosilica without high temperature thermal process, in another words, mild condition, as reported by Adam et al. [63] and Selvakumar et al. [60].

#### *2.2.5 Discussion for method*

As mentioned above, two major methods that have been widely adopted by researcher in nanosilica production are thermal and chemical methods. Fluidized bed reactor could produce high purity of nanosilica at 92–96% using thermal process at 800–950°C for 4–8 h [38]. While chemical method modified alkaline method showed promising properties, produced 95% purity nanosilica with 110°C (mild condition) [63]. It is noticed that thermal method used a lot of energy (high temperature and long reaction time) to acquire nanosilica, whereas chemical method required high usage of chemicals (acid and alkaline solution), which

**69**

**Alkaline extraction method**

**No**

1 2 3 4 6 7 8 **Alkaline modification method**

1 3 5 2 **Table 2.** *List of alkaline technique based on its parameters.*

Separating rice husk ash silica gel

from microwave heating

Acid pre-treatment before

RHA RHA

RH RHA

48 hours

150°C

—

—

—

overnight

110°C

15–91 nm

~95.5%

—

Adam et al. [63]

Rungrodnimitchai

et al. [61]

24 hours

120°C

47 nm

69–73% (250 ml

Zhang et al. [62]

Na CO 2

3 solution)

1 hour

130°C

—

85%

—

Selvakumar et al.

[60]

(1.0 N

NaOH)

conventional alkaline extraction

Using alkali solution and followed

RH RH RH RH RHA Wheat

1 hour

550°C

227 nm

—

—

Cui et al. [58]

husk ash

RHA

48 hours

80°C

—

50.15%

—

Masnar and Coorey

[59]

24 hours

60°C

—

—

24 hours

50°C

10–20 nm

—

—

80% (NaOH

concentration of

1.0 mol dm−3

)

48 hours

80°C

20–30 nm

99.48%

4 hours

700°C

20–25 nm

>95%

30 minutes

550°C

98–272 nm

—

—

—

91.91% @pH 3

Zulkifli et al. [51]

Hassan et al. [52]

by acid neutralization and undergo

thermal process (calcination)

**Method**

**Material**

**Time**

**Temperature (after getting silica gel)**

**Size**

**Purity**

**Yield**

**References**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

Liou and Yang [53]

Awizar et al. [56]

Haq et al. [57]


#### *Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

*Engineered Nanomaterials - Health and Safety*

agricultural waste by Kumar et al. [71].

Adam et al. [63] and Selvakumar et al. [60].

*2.2.5 Discussion for method*

*2.2.4 Discussion on chemical method*

XRF confirmed the purity of amorphous silica over 99%.

*2.2.3 Other chemical extraction methods of silica from agricultural waste*

was leached with hydrochloric acid and sulfuric acid to achieve pure silica. Thus,

Many chemical treatments exist for the production of silica from bio-waste. Faizul et al. [69] obtained amorphous silica and activated carbon by three effective procedures by using toluene/ethanol, NaClO2, and KOH. The method of calcination was used in the production of nano amorphous silica (100–120 nm). The manufacturing of amorphous silica was carried out using organic acid leaching instead of strong acid [70]. Ionic liquid was also used in the manufacturing of silica from

Chemical method is advisable to obtain high purity of amorphous nanosilica due to its effective chemical reaction (**Tables 2** and **3**). Basically, there are two types of extraction methods (alkaline extraction and acid extraction). In this review, alkaline extraction method is predominantly compared to acid extraction method in terms of nanosilica properties obtained. Hassan et al. [52] produced the preparation of silica nanoparticle by alkali treatment and obtained more than 95% purity of nanosilica. Furthermore, Liou and Yang [53] prepared nanosilica and obtained 99.48% of silica content throughout alkali treatment. For further improvement, Selvakumar et al. [60] used pre-treatment and result in high purity (85%) of silica contents. Similarly, Adam et al. [63] also reported acid pre-treatment before conventional alkaline method, where ~95% purity of nanosilica was obtained. As for pre-treatment is use to enhance silica purity and remove metallic impurities. Meanwhile, Rungrodnimitchai et al. [61] used 2.0 M sodium hydroxide assisted by microwave (800 W) to obtain high purity of nanosilica from RHA. The modification could enhance the properties of the nanosilica obtained from the conventional method in terms of morphology, size, and purities as presented in **Table 2**. Furthermore, acid leaching method has been presented in **Table 3**. It was found that acid leaching method produced high purity of nanosilica as reported by Bakar et al. [68], where 99% purity of nanosilica was obtained with 500–700 nm. Similarly, Mahmud et al. [66] also reported that acid leaching method produced 99% high purity of nanosilica using HCl. Referring to above, acid leaching improves the other metal removal and increases the purity of nanosilica. It is noticed that single method like alkaline extraction and acid leaching method required high temperature thermal process to acquire nanosized silica. While combination of acid leaching and alkaline method could provide high purity of nanosilica without high temperature thermal process, in another words, mild condition, as reported by

As mentioned above, two major methods that have been widely adopted by researcher in nanosilica production are thermal and chemical methods. Fluidized bed reactor could produce high purity of nanosilica at 92–96% using thermal process at 800–950°C for 4–8 h [38]. While chemical method modified alkaline method showed promising properties, produced 95% purity nanosilica with 110°C (mild condition) [63]. It is noticed that thermal method used a lot of energy (high temperature and long reaction time) to acquire nanosilica, whereas chemical method required high usage of chemicals (acid and alkaline solution), which

**68**

**Table2.**

 *List of alkaline technique based on its parameters.*

**Table 3.**

**71**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

resulted in cost intensive. Moreover, high thermal and chemical methods also contributed some bad impact on environment due to releasing of nonfriendly gases and waste materials produced, respectively. Thus, low cost and environmental friendly method is required to idealize for industrial application. In recent year, Mor et al. [72] reported a low-cost method in preparing nanosilica using green technology. Initially, the RHA was dissolved in NaOH and placed to autoclave at 100°C for 2 h to obtain the mixture slurry and followed dilution with distilled water for phase separation. The supernatant proceeds for silica extraction with filtration process. The filtrate precipitated with HCl and followed by washing and oven dried at 50°C

There are two main methods for preparing nanofluids, which are one-step and two-step methods. One-step method combines between synthesis and dispersion of nanoparticles into base fluid in one step. Several differences exist in these methods. In one of the conventional techniques called the one-step method of direct evaporation, the nanofluid is obtained inside the base fluid by solidifying the nanoparticles that are originally in the gaseous phase. Akoh et al. [73] created the one-step direct evaporation method and are referred to vacuum evaporation on the method of running oil substrates. The concept of this method was originally developed the nanoparticles in order to obtain dry nanoparticles. Particles are difficult to differentiate from liquids. The technique of laser ablation to obtain alumina nanofluids is another one-step technique [74]. Zhu et al. [75] used one-step technique to prepare

The two-step method is widely utilized for nanofluid preparation, and most of the cases used nano powders (solid) during the preparation. The technique first produces nanoparticles; thereafter, the nanoparticles will be dispersed into the base fluids. Jena et al. [76] used hydrogen reduction techniques to prepare nanoparticles from the chemical precursor and dispersed them into fluid via two-step methods. The use of ultrasonic technique to disperse the nanoparticles into deionized water, which containing sodium lauryl sulfate (SLS) during nanofluid preparation, is also

Wei and Wang [78] synthesized copper nanofluids by using a constant flow microfluidic microreactor. Through this technique, the microstructure copper nanofluids can be synthesized continually by changing parameters such as additive and flow rate and reactant concentration. Using a new precursor conversion technique, ultrasonic and microwave irradiation can be used to synthesize CuO nanofluids with a better solid volume fraction (~10 vol%) [79]. Under microwave irradiation, the Cu(OH)2 precursor will entirely converted into CuO nanoparticles in H2O. The ammonium citrate stops nanoparticles from growing and aggregating, resulted in stable CuO nanofluid with a better heat conductivity than the ones produced by using other dispersive techniques. The easier way to acquire colloids of monodisperse noble metal is by using the technique of phase transfer [80]. The two-phase cyclohexane system, aqueous formaldehyde, is transmitted to cyclohexane in water through the dodecyl amine response to cyclohexane as an intermediate form reduction. Cyclohexane solution intermediates can reduce Ag or Au ions in aqueous solution to form dodecyl amine-protected Ag and Au nanoparticles at room temperature. Feng et al. [81] used phase transfer method in preparing Au, Ag, and Pt nanoparticles based on a reduction in solubility of PVP in water at increased temperature. The technique of phase transfer is also used to prepare stable Fe3O4 nanofluids based on kerosene. Oleic acid is effectively grafted in chemisorbed

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

where high purity of nanosilica (99%) was obtained.

copper nanoparticles in the medium of ethylene glycol.

one of the widely adopted technique [77].

**3. Method of nanofluid preparation**

*List of acid leaching method based on its parameters.*

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

resulted in cost intensive. Moreover, high thermal and chemical methods also contributed some bad impact on environment due to releasing of nonfriendly gases and waste materials produced, respectively. Thus, low cost and environmental friendly method is required to idealize for industrial application. In recent year, Mor et al. [72] reported a low-cost method in preparing nanosilica using green technology. Initially, the RHA was dissolved in NaOH and placed to autoclave at 100°C for 2 h to obtain the mixture slurry and followed dilution with distilled water for phase separation. The supernatant proceeds for silica extraction with filtration process. The filtrate precipitated with HCl and followed by washing and oven dried at 50°C where high purity of nanosilica (99%) was obtained.

#### **3. Method of nanofluid preparation**

*Engineered Nanomaterials - Health and Safety*

**70**

**Acid leaching method**

**No**

1 2

Raw material

Palm ash

RH

1 hour

650°C

181.2–

—

294.7 nm

30 minutes

800°C

—

92% (6% citric acid)

—

—

Faizul et al. [64]

Carmona et al. [65]

undergoes acid

leaching at mild

condition and

followed by thermal

RH RH RH

2 hours

600°C

500–700 nm

>99%

48 hours

50°C

6 nm

98.801%

—

—

Rafiee and Shahebrahimi [67]

Bakar et al. [68]

2 hour

700°C

53–55 nm

99.761% (HCl),

—

Mahmud et al. [66]

99.760% (citric acid)

3 4 5 **Table 3.**

*List of acid leaching method based on its parameters.*

process (calcination)

**Method**

**Material**

**Time (h)**

**Temperature** 

**Size**

**Purity**

**Yield**

**References**

**(after getting** 

**silica gel)**

There are two main methods for preparing nanofluids, which are one-step and two-step methods. One-step method combines between synthesis and dispersion of nanoparticles into base fluid in one step. Several differences exist in these methods. In one of the conventional techniques called the one-step method of direct evaporation, the nanofluid is obtained inside the base fluid by solidifying the nanoparticles that are originally in the gaseous phase. Akoh et al. [73] created the one-step direct evaporation method and are referred to vacuum evaporation on the method of running oil substrates. The concept of this method was originally developed the nanoparticles in order to obtain dry nanoparticles. Particles are difficult to differentiate from liquids. The technique of laser ablation to obtain alumina nanofluids is another one-step technique [74]. Zhu et al. [75] used one-step technique to prepare copper nanoparticles in the medium of ethylene glycol.

The two-step method is widely utilized for nanofluid preparation, and most of the cases used nano powders (solid) during the preparation. The technique first produces nanoparticles; thereafter, the nanoparticles will be dispersed into the base fluids. Jena et al. [76] used hydrogen reduction techniques to prepare nanoparticles from the chemical precursor and dispersed them into fluid via two-step methods. The use of ultrasonic technique to disperse the nanoparticles into deionized water, which containing sodium lauryl sulfate (SLS) during nanofluid preparation, is also one of the widely adopted technique [77].

Wei and Wang [78] synthesized copper nanofluids by using a constant flow microfluidic microreactor. Through this technique, the microstructure copper nanofluids can be synthesized continually by changing parameters such as additive and flow rate and reactant concentration. Using a new precursor conversion technique, ultrasonic and microwave irradiation can be used to synthesize CuO nanofluids with a better solid volume fraction (~10 vol%) [79]. Under microwave irradiation, the Cu(OH)2 precursor will entirely converted into CuO nanoparticles in H2O. The ammonium citrate stops nanoparticles from growing and aggregating, resulted in stable CuO nanofluid with a better heat conductivity than the ones produced by using other dispersive techniques. The easier way to acquire colloids of monodisperse noble metal is by using the technique of phase transfer [80]. The two-phase cyclohexane system, aqueous formaldehyde, is transmitted to cyclohexane in water through the dodecyl amine response to cyclohexane as an intermediate form reduction. Cyclohexane solution intermediates can reduce Ag or Au ions in aqueous solution to form dodecyl amine-protected Ag and Au nanoparticles at room temperature. Feng et al. [81] used phase transfer method in preparing Au, Ag, and Pt nanoparticles based on a reduction in solubility of PVP in water at increased temperature. The technique of phase transfer is also used to prepare stable Fe3O4 nanofluids based on kerosene. Oleic acid is effectively grafted in chemisorbed

fashion on the surface of Fe3O4 nanoparticles, enabling Fe3O4 nanoparticles to be well compatible with kerosene [82]. The phase-transfer technique prepared Fe3O4 nanofluids not showing "time reliance of the characteristic of heat conductivity" as reported previously. The main problem is the production of nanofluids with a controllable microstructure. It is well recognized that nanofluid characteristics are highly dependent on nanomaterial structure and shape. Recent study demonstrates the improvement in conductivity and the stability of nanofluids when synthesized using chemical solution compared to other techniques [83]. This technique is differentiated by its controllability from others. The microstructure of nanofluids can be differed and manipulated by regulating the factors of synthesis, including acidity, radiation from the microwave and ultrasonic, temperature, acidity, concentrations, and types of reactor and the order of additives added to the solution.

Silica is widely used as both precursor and material for ceramic product manufactures. Silica has high abrasion resistance, high thermal stability, and electrical insulation [84]. Fazeli et al. [85] dispersed nanosilica into the distilled water, and the suspension was sonicated for at least 90 min in an ultrasonic bath. They discovered that silica nanofluids remained stable without visible settlement for 72 hours. Pang et al. [86] used ultrasonic to mix SiO2-pure methanol by ultrasonic (750 W, 20 kHz) and Al2O3-pure methanol to break the agglomeration through vibration during 2 hours. They examined the impact of the zeta potential and pH of methanol-based nanofluids in nanoparticles. They proved that the zeta potential is closely connected with the pH of the suspension. Al2O3 nanofluids have zeta potential >60 mV; meanwhile, SiO2 nanofluids have zeta potential >30 mV, which indicated that both nanofluids were well stable. The visualization and Tyndall effect (light dispersion study in nanoparticles) images show that nanofluids based on methanol are well dispersed. Bolukbasi and Ciloglu [87] have been using magnetic stirrer to prepare SiO2 nanofluids. The suspensions were continuously sonicated for 2 hours into an ultrasonic vibrator (600 W and 40 kHz). The researcher confirmed that no sedimentation was traced throughout the experimental period. Darzi et al. [88] applied distilled water to the specified quantity of SiO2 nanoparticles and mixed for half an hour with a magnetic stirrer. Afterward, the ultrasonic vibrator was dispersed for 2 hours to have the stable suspension. During the synthesis method, no surfactant/dispersant additives were added, otherwise affecting the thermophysical characteristics of nanofluid. Silica nanoparticles were used to function through grafting silanes directly on the silica nanoparticles surfaced by Yang and Liu [89]. For the functioning method, silane of (3-glycidoxylproyl) trimethyoxysilane has been used as the reacting silane and silica nanoparticles with a mass ratio of 0.115. Nanoparticles were successfully dispersed into water. Meanwhile, the solution was stored at 50°C for 12 hours of ambient temperature. Functional nanoparticles were discovered to continue to disperse even when the nanofluid remained at a mass concentration of 10% for 12 months. In addition, no sedimentation has been reported. They prepared traditional nanoparticles by dispersing and oscillating them to water. Powder of silica nanoparticles was first dissipated into deionized water and then oscillated in an ultrasound bath for 12 hours. Sedimentation was found after a few days. Anoop et al. [90] dispersed SiO2 nanoparticles with an ultrasound bath in deionized water for 30 minutes. In addition, the application of a sonicator type probe to the nanofluids intensified this colloidal suspension. The suspension was provided by cyclic ultrasonic pulses for around 15 minutes in order to obtain maximum particle de-agglomeration. By adding nitric acid reagent grade from the isoelectric pH value, the pH value of the suspension was kept at 4.5. Nanofluids have been indicated to show excellent stability over period. Qu and Wu [91] developed nanofluids Al2O3 and SiO2 water. The pH value of the nanofluids was modified as a first step to a value that was far from the respective isoelectric point

**73**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

(IEP) of silica (with pH ~ 3) or alumina (with pH ~ 9), then added to the water nanoparticles (with pH ~ 9) and with pH ~9. The dispersion solution was vibrated in an ultrasonic bath for about 4 hours afterward. Alumina nanoparticles have been discovered to be better dispersed. Hwang et al. [92] generated CuO, MWCNT, and SiO2 nanofluids by using an ultrasonic disruptor. For SiO2 and CuO nanoparticles, they acquired stable suspensions. Nevertheless, sodium dodecyl sulfate (SDS) has been used as a surfactant to produce MWCNT nanofluids as the MWCNTs are

Nanofluids have been proved in experiment and theory in enhancing heat transport and energy efficiency for various manufacturing purposes such as mechanical applications, electronic cooling, transportation, and many more in a range of thermal exchange technologies. In all applications, nanofluid performs a key position in creating the next device generation for various medical and engineering

The temporal difference between energy supply and energy requires rendered storage system design. Stocking of thermal electricity as in solar thermal installations as sensitive and latent heat, with an emphasis on an effective use as well as preservation of wastewater and solar energy in buildings and manufacturing, has become an significant element in energy planning [93]. Compared to the basic material, the PCMs contained extremely high thermal conductivity. Liu et al. [94] synthesized a new type of nanofluid phase change material (PCM) with a tiny portion of TiO2 nanoparticles suspended in aqueous saturated BaCl2 solution. The PCM nanofluids had relatively better thermal conductivity compared to base material. The cool storage/supply rate and the cool storage/supply capability have risen significantly compared with aqueous solution of BaCl2 without the need of additional nanoparticles. The greater thermal characteristics of PCMs show that in cool storage applications, they have the ability to replace standard PCMs. Copper nanoparticles are the additives that are efficient to enhance PCM cooling and heating levels. Shin and Banerjee [95] recorded an anomalous increase in nanofluid-specific heat capacity of high temperature. The researcher discovered that 1 wt% SiO2 nanoparticledoped alkali metal chloride salt eutectic improves the specific thermal capacity of nanofluid by ~15% to be used in solar thermal energy storage facilities. One of the methods used to store solar energy is the use of PCMs. Paraffin is the most appropriate of many accessible PCMs because of its attractive features, including large latent heat capacity, insignificant super cooling, and low cost. The intrinsic low thermal conductivity (0.21–0.24 W/mK), however, avoids possible applications [96]. Wu et al. [96] numerically researched Cu/paraffin nanofluid PCM melting procedures. Their findings showed that the melting time with 1 wt% Cu/paraffin is saved by 13.1%. The study found that the addition of nanoparticles is an effective

applications. Some of the following applications are discussed below.

way for increasing the heat transfer of latent heat energy storage system.

more sun energy than the world consumes for a year [97, 98].

Solar energy is an important factor in energy use because of a shortage of electricity generation. Lack of fossil fuel and environmental factors will limit future use of fossil fuels. Researchers are encouraged to discover alternative energy sources. This became even more widespread as fossil fuel prices continue to increase. In latest years, solar energy has had a notable advantage. In just 1 hour, the earth gets

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

entangled and aggregated into aqueous suspension.

**4. Potential application of nanofluids**

**4.1 Solar applications**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

(IEP) of silica (with pH ~ 3) or alumina (with pH ~ 9), then added to the water nanoparticles (with pH ~ 9) and with pH ~9. The dispersion solution was vibrated in an ultrasonic bath for about 4 hours afterward. Alumina nanoparticles have been discovered to be better dispersed. Hwang et al. [92] generated CuO, MWCNT, and SiO2 nanofluids by using an ultrasonic disruptor. For SiO2 and CuO nanoparticles, they acquired stable suspensions. Nevertheless, sodium dodecyl sulfate (SDS) has been used as a surfactant to produce MWCNT nanofluids as the MWCNTs are entangled and aggregated into aqueous suspension.

#### **4. Potential application of nanofluids**

Nanofluids have been proved in experiment and theory in enhancing heat transport and energy efficiency for various manufacturing purposes such as mechanical applications, electronic cooling, transportation, and many more in a range of thermal exchange technologies. In all applications, nanofluid performs a key position in creating the next device generation for various medical and engineering applications. Some of the following applications are discussed below.

#### **4.1 Solar applications**

*Engineered Nanomaterials - Health and Safety*

fashion on the surface of Fe3O4 nanoparticles, enabling Fe3O4 nanoparticles to be well compatible with kerosene [82]. The phase-transfer technique prepared Fe3O4 nanofluids not showing "time reliance of the characteristic of heat conductivity" as reported previously. The main problem is the production of nanofluids with a controllable microstructure. It is well recognized that nanofluid characteristics are highly dependent on nanomaterial structure and shape. Recent study demonstrates the improvement in conductivity and the stability of nanofluids when synthesized using chemical solution compared to other techniques [83]. This technique is differentiated by its controllability from others. The microstructure of nanofluids can be differed and manipulated by regulating the factors of synthesis, including acidity, radiation from the microwave and ultrasonic, temperature, acidity, concentrations,

Silica is widely used as both precursor and material for ceramic product manufactures. Silica has high abrasion resistance, high thermal stability, and electrical insulation [84]. Fazeli et al. [85] dispersed nanosilica into the distilled water, and the suspension was sonicated for at least 90 min in an ultrasonic bath. They discovered that silica nanofluids remained stable without visible settlement for 72 hours. Pang et al. [86] used ultrasonic to mix SiO2-pure methanol by ultrasonic (750 W, 20 kHz) and Al2O3-pure methanol to break the agglomeration through vibration during 2 hours. They examined the impact of the zeta potential and pH of methanol-based nanofluids in nanoparticles. They proved that the zeta potential is closely connected with the pH of the suspension. Al2O3 nanofluids have zeta potential >60 mV; meanwhile, SiO2 nanofluids have zeta potential >30 mV, which indicated that both nanofluids were well stable. The visualization and Tyndall effect (light dispersion study in nanoparticles) images show that nanofluids based on methanol are well dispersed. Bolukbasi and Ciloglu [87] have been using magnetic stirrer to prepare SiO2 nanofluids. The suspensions were continuously sonicated for 2 hours into an ultrasonic vibrator (600 W and 40 kHz). The researcher confirmed that no sedimentation was traced throughout the experimental period. Darzi et al. [88] applied distilled water to the specified quantity of SiO2 nanoparticles and mixed for half an hour with a magnetic stirrer. Afterward, the ultrasonic vibrator was dispersed for 2 hours to have the stable suspension. During the synthesis method, no surfactant/dispersant additives were added, otherwise affecting the thermophysical characteristics of nanofluid. Silica nanoparticles were used to function through grafting silanes directly on the silica nanoparticles surfaced by Yang and Liu [89]. For the functioning method, silane of (3-glycidoxylproyl) trimethyoxysilane has been used as the reacting silane and silica nanoparticles with a mass ratio of 0.115. Nanoparticles were successfully dispersed into water. Meanwhile, the solution was stored at 50°C for 12 hours of ambient temperature. Functional nanoparticles were discovered to continue to disperse even when the nanofluid remained at a mass concentration of 10% for 12 months. In addition, no sedimentation has been reported. They prepared traditional nanoparticles by dispersing and oscillating them to water. Powder of silica nanoparticles was first dissipated into deionized water and then oscillated in an ultrasound bath for 12 hours. Sedimentation was found after a few days. Anoop et al. [90] dispersed SiO2 nanoparticles with an ultrasound bath in deionized water for 30 minutes. In addition, the application of a sonicator type probe to the nanofluids intensified this colloidal suspension. The suspension was provided by cyclic ultrasonic pulses for around 15 minutes in order to obtain maximum particle de-agglomeration. By adding nitric acid reagent grade from the isoelectric pH value, the pH value of the suspension was kept at 4.5. Nanofluids have been indicated to show excellent stability over period. Qu and Wu [91] developed nanofluids Al2O3 and SiO2 water. The pH value of the nanofluids was modified as a first step to a value that was far from the respective isoelectric point

and types of reactor and the order of additives added to the solution.

**72**

The temporal difference between energy supply and energy requires rendered storage system design. Stocking of thermal electricity as in solar thermal installations as sensitive and latent heat, with an emphasis on an effective use as well as preservation of wastewater and solar energy in buildings and manufacturing, has become an significant element in energy planning [93]. Compared to the basic material, the PCMs contained extremely high thermal conductivity. Liu et al. [94] synthesized a new type of nanofluid phase change material (PCM) with a tiny portion of TiO2 nanoparticles suspended in aqueous saturated BaCl2 solution. The PCM nanofluids had relatively better thermal conductivity compared to base material. The cool storage/supply rate and the cool storage/supply capability have risen significantly compared with aqueous solution of BaCl2 without the need of additional nanoparticles. The greater thermal characteristics of PCMs show that in cool storage applications, they have the ability to replace standard PCMs. Copper nanoparticles are the additives that are efficient to enhance PCM cooling and heating levels. Shin and Banerjee [95] recorded an anomalous increase in nanofluid-specific heat capacity of high temperature. The researcher discovered that 1 wt% SiO2 nanoparticledoped alkali metal chloride salt eutectic improves the specific thermal capacity of nanofluid by ~15% to be used in solar thermal energy storage facilities. One of the methods used to store solar energy is the use of PCMs. Paraffin is the most appropriate of many accessible PCMs because of its attractive features, including large latent heat capacity, insignificant super cooling, and low cost. The intrinsic low thermal conductivity (0.21–0.24 W/mK), however, avoids possible applications [96]. Wu et al. [96] numerically researched Cu/paraffin nanofluid PCM melting procedures. Their findings showed that the melting time with 1 wt% Cu/paraffin is saved by 13.1%. The study found that the addition of nanoparticles is an effective way for increasing the heat transfer of latent heat energy storage system.

Solar energy is an important factor in energy use because of a shortage of electricity generation. Lack of fossil fuel and environmental factors will limit future use of fossil fuels. Researchers are encouraged to discover alternative energy sources. This became even more widespread as fossil fuel prices continue to increase. In latest years, solar energy has had a notable advantage. In just 1 hour, the earth gets more sun energy than the world consumes for a year [97, 98].

Solar collectors are specific types of heat exchangers that convert solar energy to transport medium internal energy. This equipment absorbs incoming sunlight, which is converted into heat and transmitted the heat to a fluid that flows through the collector (generally oil, air, and water). The energy is collected directly from the working fluid to the hot water or space conditioning or thermal energy storage tank, for night or on cloudy days [99].

Taylor et al. [100] found that the use of the graphite/therminol VP-1 nanofluid with volume fractions around 0.001% or less could be of benefit for 10–100 MWe energy crops. In combination with a solar thermal power tower with 100 MWe of capacity in a solar resource such as Tucson, Arizona, the researchers estimated that \$3.5 million more could be achieved each year. The supply of fresh water is more crucial arid distant areas of the globe. Solar desalination technologies are possible to overcome portion of the issue in these areas, where solar energy is accessible. The absence and untrustworthy drinking water is a main issue in developing countries. Global dryness and desertification are estimated to make drinking water a major problem in the world [101].

Greenhouse gas emission from fresh water production can be prevented by solar stills [102]. Many experts have researched solar stills and used different techniques to enhance their productivity. Gnanadason et al. [103] found that the productivity of solar system was influenced by nanofluids. The implications of putting carbon nanotubes (CNTs) to the water in a single solar basin were investigated. The findings have shown the addition of nanofluids that will enhance the efficiency by 50%. However, the quantity of nanofluid added to the water inside the solar was not yet mentioned. In addition to solar nanofluids, the economic growth should be perceived. Certain works in the literature disclosed the addition of dyes to solar stills could increase the efficiency. Nijmeh et al. [104] investigated that adding violet color to the solar water still improves the efficiency significantly by 29%. Furthermore, nanofluids (especially the CNTs) are more expensive, and this might therefore be a difficult task for the use of nanofluids in solar stills because the nanofluids in solar stills do not flow in a closed loop in order to recover them.

#### **4.2 Automobile applications**

Adding nanotubes and nanoparticles to the conventional engine coolants (ethylene glycol and water mixture), nanofluid lubricants can boost their thermal conductivity and enhance heat change rates and fuel economy [105]. Tzeng et al. [106] have studied the impacts of nanofluids on automatic transmission cooling. They spread CuO and Al2O3 nanoparticles and antifoams into the transmission fluid and then used four-wheel automatic transmission on a real-time basis. The findings indicate that CuO nanofluid has the lowest temperature distribution and the highest heat transfer impact on the rotating speeds [107]. CuO and nanofluids based on aluminum oxides were developed with the arc-submerged nanoparticle synthesis system along with the plasma charging arc system [108, 109]. Both types of nanofluids have increased the characteristics, including a greater boiling point, a greater viscosity, and a greater conductivity than conventional brake fluid. With greater viscosity, conductivity, and boiling point, the brake oil nanofluids reduce the vapor lock from occurring and offer greater safety in driving condition [110].

#### **4.3 Electronic cooling**

As IC (embedded circuit) and microelectronic parts decrease in size, the energy dissipation has risen dramatically. Better thermal management and cooling liquids are necessary for secure operation, with enhanced heat transport characteristics.

**75**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

ting features of the surface. Concentrations as low as 3 × 10<sup>−</sup><sup>6</sup>

Nanofluids were regarded as working liquids for electronic cooling applications in heat pipes. Tsai et al. [111] used water-based nanofluid as the operating channel for circular heat pipe. It was intended as a heat diffuser and applied in CPU of notebook or desktop PC. The findings exhibited that the nanofluid heat pipes have considerably lower thermal resistance than deionized water. The findings showed that the thermal strength of a vertical meshed heat tube differs respectively with nanoparticle size. Ma et al. [112] examined the impact of nanofluids toward oscillating heat pipe transport capability. The experimental results reveal that the temperature difference between the evaporator and the condenser decreased from 40.9 to 24.3°C at an input energy of 80 W by 1 vol% nanoparticles. Lin et al. [113] examined nanofluids using silver nanoparticles in heat pulsating pipes and found supportive outcomes. The silver nanofluid enhanced the thermal transfer properties of the heat pipes. Vafaei et al. [114] found that nanofluids are efficient in engineering surface wettability and potentially surface tension. With a goniometer, the presence of a very small bismuth telluride nanofluid concentration significantly affected the wet-

angle to more than 40°, showing clearly nanoparticles affect the force balance triple line vicinity. Experimental, numerical, and theoretical studies on nanofluid prove numerous prospective applications of nanofluids are present such as electronic cooling, displays, micro devices, cameras, thermal exchangers, military, spacecraft equipment, boats, medicine, atomic reactors, fuel cell and sensor applications. The stability of nanofluids is a major challenge for nanofluid commercialization. By solving the problems, significant developments are anticipated in many applications. Further study should be conducted on numerous heat and fluid applications.

Some special types of nanoparticles possess antibacterial activity or drug delivery properties, so that nanofluids that contain these nanoparticles have certain relevant properties [110]. Organic antibacterial products, especially at high temperatures or pressures, are often less stable. Consequently, inorganic materials such as metal oxides and metal have received considerable attention in the previous decade because they are able to resist severe process circumstances. ZnO nanofluid antibacterial behavior indicates that ZnO nanofluids are bacteriostatic to *Escherichia coli*. With the growing concentration of nanoparticles, antibacterial activity rises and the particle size decreases. Measurements of electrochemical show a direct interaction between ZnO and elevated ZnO levels of bacterial membrane (L. [115]). Jalal et al. [116] created ZnO nanoparticles with a green technique. An estimation of the reduction ratio of ZnO-treated bacteria was made on ZnO suspension activity of nanoparticles with *E. coli*, the bacteria's survival ratio reduces with increased nanofluid ZnO levels and time. Silver nanoparticles were discovered to depend on the size of silver particles for their antibacterial activity. Antibacterial efficiency was achieved by the very small silver concentration of 1.69 mug/mL Ag [117]. Lyon and Alvarez [118] suggested that C60 suspensions exhibit ROS-independent oxidative stress in bacteria that show protein oxidation, modifications in cell membrane potential, and cellular respiration interruption. The mechanism needs direct contact between bacterial and nanoparticles as well as contrast from nanomaterial antibacterial processes earlier reported involving ROS

generation (metal oxides), or leaching of toxic components (nanosilver).

It was found that nanoparticles added to the base fluid improve the characteristics of fluids such as structure, thermal conductivity, viscosity, convective heat

improved the contact

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

**4.4 Biomedical applications**

**4.5 Discussion for applications**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

Nanofluids were regarded as working liquids for electronic cooling applications in heat pipes. Tsai et al. [111] used water-based nanofluid as the operating channel for circular heat pipe. It was intended as a heat diffuser and applied in CPU of notebook or desktop PC. The findings exhibited that the nanofluid heat pipes have considerably lower thermal resistance than deionized water. The findings showed that the thermal strength of a vertical meshed heat tube differs respectively with nanoparticle size. Ma et al. [112] examined the impact of nanofluids toward oscillating heat pipe transport capability. The experimental results reveal that the temperature difference between the evaporator and the condenser decreased from 40.9 to 24.3°C at an input energy of 80 W by 1 vol% nanoparticles. Lin et al. [113] examined nanofluids using silver nanoparticles in heat pulsating pipes and found supportive outcomes. The silver nanofluid enhanced the thermal transfer properties of the heat pipes. Vafaei et al. [114] found that nanofluids are efficient in engineering surface wettability and potentially surface tension. With a goniometer, the presence of a very small bismuth telluride nanofluid concentration significantly affected the wetting features of the surface. Concentrations as low as 3 × 10<sup>−</sup><sup>6</sup> improved the contact angle to more than 40°, showing clearly nanoparticles affect the force balance triple line vicinity. Experimental, numerical, and theoretical studies on nanofluid prove numerous prospective applications of nanofluids are present such as electronic cooling, displays, micro devices, cameras, thermal exchangers, military, spacecraft equipment, boats, medicine, atomic reactors, fuel cell and sensor applications. The stability of nanofluids is a major challenge for nanofluid commercialization. By solving the problems, significant developments are anticipated in many applications. Further study should be conducted on numerous heat and fluid applications.

#### **4.4 Biomedical applications**

*Engineered Nanomaterials - Health and Safety*

tank, for night or on cloudy days [99].

problem in the world [101].

**4.2 Automobile applications**

**4.3 Electronic cooling**

Solar collectors are specific types of heat exchangers that convert solar energy to transport medium internal energy. This equipment absorbs incoming sunlight, which is converted into heat and transmitted the heat to a fluid that flows through the collector (generally oil, air, and water). The energy is collected directly from the working fluid to the hot water or space conditioning or thermal energy storage

Taylor et al. [100] found that the use of the graphite/therminol VP-1 nanofluid with volume fractions around 0.001% or less could be of benefit for 10–100 MWe energy crops. In combination with a solar thermal power tower with 100 MWe of capacity in a solar resource such as Tucson, Arizona, the researchers estimated that \$3.5 million more could be achieved each year. The supply of fresh water is more crucial arid distant areas of the globe. Solar desalination technologies are possible to overcome portion of the issue in these areas, where solar energy is accessible. The absence and untrustworthy drinking water is a main issue in developing countries. Global dryness and desertification are estimated to make drinking water a major

Greenhouse gas emission from fresh water production can be prevented by solar stills [102]. Many experts have researched solar stills and used different techniques to enhance their productivity. Gnanadason et al. [103] found that the productivity of solar system was influenced by nanofluids. The implications of putting carbon nanotubes (CNTs) to the water in a single solar basin were investigated. The findings have shown the addition of nanofluids that will enhance the efficiency by 50%. However, the quantity of nanofluid added to the water inside the solar was not yet mentioned. In addition to solar nanofluids, the economic growth should be perceived. Certain works in the literature disclosed the addition of dyes to solar stills could increase the efficiency. Nijmeh et al. [104] investigated that adding violet color to the solar water still improves the efficiency significantly by 29%. Furthermore, nanofluids (especially the CNTs) are more expensive, and this might therefore be a difficult task for the use of nanofluids in solar stills because the nanofluids in solar stills do not flow in a closed loop in order to recover them.

Adding nanotubes and nanoparticles to the conventional engine coolants (ethylene glycol and water mixture), nanofluid lubricants can boost their thermal conductivity and enhance heat change rates and fuel economy [105]. Tzeng et al. [106] have studied the impacts of nanofluids on automatic transmission cooling. They spread CuO and Al2O3 nanoparticles and antifoams into the transmission fluid and then used four-wheel automatic transmission on a real-time basis. The findings indicate that CuO nanofluid has the lowest temperature distribution and the highest heat transfer impact on the rotating speeds [107]. CuO and nanofluids based on aluminum oxides were developed with the arc-submerged nanoparticle synthesis system along with the plasma charging arc system [108, 109]. Both types of nanofluids have increased the characteristics, including a greater boiling point, a greater viscosity, and a greater conductivity than conventional brake fluid. With greater viscosity, conductivity, and boiling point, the brake oil nanofluids reduce the vapor

lock from occurring and offer greater safety in driving condition [110].

As IC (embedded circuit) and microelectronic parts decrease in size, the energy dissipation has risen dramatically. Better thermal management and cooling liquids are necessary for secure operation, with enhanced heat transport characteristics.

**74**

Some special types of nanoparticles possess antibacterial activity or drug delivery properties, so that nanofluids that contain these nanoparticles have certain relevant properties [110]. Organic antibacterial products, especially at high temperatures or pressures, are often less stable. Consequently, inorganic materials such as metal oxides and metal have received considerable attention in the previous decade because they are able to resist severe process circumstances. ZnO nanofluid antibacterial behavior indicates that ZnO nanofluids are bacteriostatic to *Escherichia coli*. With the growing concentration of nanoparticles, antibacterial activity rises and the particle size decreases. Measurements of electrochemical show a direct interaction between ZnO and elevated ZnO levels of bacterial membrane (L. [115]). Jalal et al. [116] created ZnO nanoparticles with a green technique. An estimation of the reduction ratio of ZnO-treated bacteria was made on ZnO suspension activity of nanoparticles with *E. coli*, the bacteria's survival ratio reduces with increased nanofluid ZnO levels and time. Silver nanoparticles were discovered to depend on the size of silver particles for their antibacterial activity. Antibacterial efficiency was achieved by the very small silver concentration of 1.69 mug/mL Ag [117]. Lyon and Alvarez [118] suggested that C60 suspensions exhibit ROS-independent oxidative stress in bacteria that show protein oxidation, modifications in cell membrane potential, and cellular respiration interruption. The mechanism needs direct contact between bacterial and nanoparticles as well as contrast from nanomaterial antibacterial processes earlier reported involving ROS generation (metal oxides), or leaching of toxic components (nanosilver).

#### **4.5 Discussion for applications**

It was found that nanoparticles added to the base fluid improve the characteristics of fluids such as structure, thermal conductivity, viscosity, convective heat transfer, density, and specific heat. In our review, we have narrowed down the application of nanofluids such as solar, automobile, electronic cooling, and biomedical application. It is noticed that the physical properties of nanoparticles such as size and crystallinity are influencing the nanofluid performance during its application. For instance, Micali et al. [119] explored the possibility to reduce temperature up to 13.6% on the exhaust valve seat and up to 4.1% on the exhaust valve spindle by 2.5% volume concentration on the cylinder head and the spindle of the exhaust valve. Al-Jethelah et al. [120] discovered improvements of solar thermal applications in terms of melting process through numerical and experimental by adding nanofluids into PCM. Said et al. [121] prepared 0.3% volume fraction of Al2O3 nanofluids and dispersed into distilled water and ethylene glycol as base fluid (ratio of 50:50) and discovered that it enhances the thermal performance by 24.21%. We believe that RH-derived nanosilica will provide similar performance compared to other semiconductor nanoparticles as mentioned above. Akilu et al. [122] attained ~27% thermal conductivity enrichment at 21.1% disparagement of specific heat by using hybrid nanofluids, and SiO2-CuO (0.5–2 vol%) dispersed into base fluid (Glycerol/EG). Yao et al. [123] did the research on the boiling efficiency of Al2O3, SiO2, and their mixture with water at the ratio of 1:1. The significance of their study was its impact of pressure on the performance of boiling nanofluids. Based on the outcomes, nanofluid efficiency increased the pressure reduction. Authors also regarded the effects of nanoparticle size on the heat flux posed tiny rise while raising the nanoparticle size between 30 and 50 nm.

#### **5. Conclusion**

This book chapter collectively reviews the preparation method of rice husk nanosilica, its application as nanofluids, and nanofluid application in the industry. There are two main methods in preparing nanosilica, namely thermal and chemical methods. It is noticed that chemical method is more preferable than thermal method in terms of nanosilica purity, which is critical. The popular chemical methods widely used by the researcher are alkaline extraction and acid leaching method. It has found that utilizing solely single chemical method must follow high thermal treatment and high operating cost, which is not feasible. Thus, a combination or modification of the chemical method is required to improve the purity of nanosilica. Pre-acid treatment followed by conventional alkaline extraction presented better purity of nanosilica. The purity of nanosilica is a crucial property in nanofluid preparation, which will affect the performance of the nanofluids. There are one-step and two-step methods, which are widely adopted by the researcher in preparing nanofluids. One-step technique combines the production of nanoparticles and dispersion of nanoparticles into the base fluid with a single step. Meanwhile, in two-step method, nanoparticles are first produced and then dispersed into the base fluids. However, two-step method is preferable for rice husk nanosilica-based nanofluid preparation, which involves ultrasonic method. The application of the nanofluids has been explored such as solar application, automobile application, electronic cooling application, and biomedical application. It was found that nanofluids could improve the base fluid performance due to the additional of the nanoparticles. Even though the review focused on semiconductor-based nanofluids, we believe that rice husk nanosilica-based nanofluids could also have the similar trends of performance. Gradually, the awareness on the usage of "green" material in the product is rising, and rice husk nanosilica could be an ideal candidate as nanoparticle and nanofluid application.

**77**

**Author details**

Huei Ruey Ong1

Malaysia, Pahang, Malaysia

Pahang, Gambang, Pahang, Malaysia

provided the original work is properly cited.

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

\*, Wan Mohd Eqhwan Iskandar1

1 Faculty of Engineering and Technology, DRB-HICOM University of Automotive

2 Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia

\*Address all correspondence to: roi\_rui86@hotmail.com; hueiruey@dhu.edu.my

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Md. Maksudur Rahman Khan2

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

## **Author details**

*Engineered Nanomaterials - Health and Safety*

raising the nanoparticle size between 30 and 50 nm.

**5. Conclusion**

transfer, density, and specific heat. In our review, we have narrowed down the application of nanofluids such as solar, automobile, electronic cooling, and biomedical application. It is noticed that the physical properties of nanoparticles such as size and crystallinity are influencing the nanofluid performance during its application. For instance, Micali et al. [119] explored the possibility to reduce temperature up to 13.6% on the exhaust valve seat and up to 4.1% on the exhaust valve spindle by 2.5% volume concentration on the cylinder head and the spindle of the exhaust valve. Al-Jethelah et al. [120] discovered improvements of solar thermal applications in terms of melting process through numerical and experimental by adding nanofluids into PCM. Said et al. [121] prepared 0.3% volume fraction of Al2O3 nanofluids and dispersed into distilled water and ethylene glycol as base fluid (ratio of 50:50) and discovered that it enhances the thermal performance by 24.21%. We believe that RH-derived nanosilica will provide similar performance compared to other semiconductor nanoparticles as mentioned above. Akilu et al. [122] attained ~27% thermal conductivity enrichment at 21.1% disparagement of specific heat by using hybrid nanofluids, and SiO2-CuO (0.5–2 vol%) dispersed into base fluid (Glycerol/EG). Yao et al. [123] did the research on the boiling efficiency of Al2O3, SiO2, and their mixture with water at the ratio of 1:1. The significance of their study was its impact of pressure on the performance of boiling nanofluids. Based on the outcomes, nanofluid efficiency increased the pressure reduction. Authors also regarded the effects of nanoparticle size on the heat flux posed tiny rise while

This book chapter collectively reviews the preparation method of rice husk nanosilica, its application as nanofluids, and nanofluid application in the industry. There are two main methods in preparing nanosilica, namely thermal and chemical methods. It is noticed that chemical method is more preferable than thermal method in terms of nanosilica purity, which is critical. The popular chemical methods widely used by the researcher are alkaline extraction and acid leaching method. It has found that utilizing solely single chemical method must follow high thermal treatment and high operating cost, which is not feasible. Thus, a combination or modification of the chemical method is required to improve the purity of nanosilica. Pre-acid treatment followed by conventional alkaline extraction presented better purity of nanosilica. The purity of nanosilica is a crucial property in nanofluid preparation, which will affect the performance of the nanofluids. There are one-step and two-step methods, which are widely adopted by the researcher in preparing nanofluids. One-step technique combines the production of nanoparticles and dispersion of nanoparticles into the base fluid with a single step. Meanwhile, in two-step method, nanoparticles are first produced and then dispersed into the base fluids. However, two-step method is preferable for rice husk nanosilica-based nanofluid preparation, which involves ultrasonic method. The application of the nanofluids has been explored such as solar application, automobile application, electronic cooling application, and biomedical application. It was found that nanofluids could improve the base fluid performance due to the additional of the nanoparticles. Even though the review focused on semiconductor-based nanofluids, we believe that rice husk nanosilica-based nanofluids could also have the similar trends of performance. Gradually, the awareness on the usage of "green" material in the product is rising, and rice husk nanosilica could be an ideal candidate as nanoparticle and nanofluid

**76**

application.

Huei Ruey Ong1 \*, Wan Mohd Eqhwan Iskandar1 and Md. Maksudur Rahman Khan2

1 Faculty of Engineering and Technology, DRB-HICOM University of Automotive Malaysia, Pahang, Malaysia

2 Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, Gambang, Pahang, Malaysia

\*Address all correspondence to: roi\_rui86@hotmail.com; hueiruey@dhu.edu.my

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[99] Kalogirou SA. Solar Energy Engineering: Processes and Systems. United States of America: Academic Press; 2013. ISBN: 9780123972705

[100] Taylor RA, Phelan PE, Otanicar TP, Walker CA, Nguyen M, Trimble S, et al. Applicability of nanofluids in high flux solar collectors. Journal of Renewable and Sustainable Energy. 2011;**3**(2):023104

[101] Badran OO, Abu-Khader MM. Evaluating thermal performance of a single slope solar still. Heat and Mass Transfer. 2007;**43**(10):985-995

[102] Kianifar A, Heris SZ, Mahian O. Exergy and economic analysis of a pyramid-shaped solar water purification system: Active and passive cases. Energy. 2012;**38**(1):31-36

[103] Gnanadason MK, Kumar PS, Rajakumar S, Yousuf MS. Effect of nanofluids in a vacuum single basin solar still. International Journal of Advanced Engineering Research and Studies. 2011;**1**:171-177

[104] Nijmeh S, Odeh S, Akash B. Experimental and theoretical study of a single-basin solar sill in Jordan. International Communications in Heat and Mass Transfer. 2005;**32**(3-4):565-572

[105] Shanthi R, Anandan SS, Ramalingam V. Heat transfer enhancement using nanofluids. Thermal Science. 2012;**16**(2):423-444

[106] Tzeng S-C, Lin C-W, Huang K. Heat transfer enhancement of nanofluids in rotary blade coupling of four-wheel-drive vehicles. Acta Mechanica. 2005;**179**(1-2):11-23

[107] Popa I, Gillies G, Papastavrou G, Borkovec M. Attractive and repulsive electrostatic forces between positively charged latex particles in the presence of anionic linear polyelectrolytes. The Journal of Physical Chemistry B. 2010;**114**(9):3170-3177

[108] Kao M-J, Chang H, Wu Y-Y, Tsung T-T, Lin H-M. Producing aluminumoxide brake nanofluids using plasma charging system. Journal of the Chinese Society of Mechanical Engineers. 2007a;**28**(2):123-131

[109] Kao M, Lo C, Tsung T, Wu Y, Jwo C, Lin H. Copper-oxide brake nanofluid manufactured using arc-submerged nanoparticle synthesis system. Journal of Alloys and Compounds. 2007;**434**:672-674

[110] Yu W, Xie H. A review on nanofluids: Preparation, stability mechanisms, and applications. Journal of Nanomaterials. 2012;**2012**:435873

[111] Tsai C, Chien H, Ding P, Chan B, Luh T, Chen P. Effect of structural character of gold nanoparticles in nanofluid on heat pipe thermal performance. Materials Letters. 2004;**58**(9):1461-1465

[112] Ma H, Wilson C, Borgmeyer B, Park K, Yu Q, Choi S, et al. Effect of nanofluid on the heat transport capability in an oscillating heat pipe. Applied Physics Letters. 2006;**88**(14):143116

[113] Lin Y-H, Kang S-W, Chen H-L. Effect of silver nano-fluid on pulsating heat pipe thermal performance. Applied Thermal Engineering. 2008;**28**(11-12):1312-1317

[114] Vafaei S, Borca-Tasciuc T, Podowski M, Purkayastha A, Ramanath G, Ajayan P. Effect of nanoparticles on sessile droplet contact angle. Nanotechnology. 2006;**17**(10):2523

**85**

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids*

Solar Energy Materials and Solar Cells.

[123] Yao S, Huang X, Song Y, Shen Y, Zhang S. Effects of nanoparticle types and size on boiling feat transfer

performance under different pressures. AIP Advances. 2018;**8**(2):025005

2018;**179**:118-128

*DOI: http://dx.doi.org/10.5772/intechopen.89904*

Povey M, York D. Investigation into the antibacterial behaviour of suspensions of ZnO nanoparticles (ZnO nanofluids). Journal of Nanoparticle Research.

[115] Zhang L, Jiang Y, Ding Y,

[116] Jalal R, Goharshadi EK, Abareshi M, Moosavi M, Yousefi A, Nancarrow P. ZnO nanofluids: Green

synthesis, characterization, and antibacterial activity.

2010;**121**(1-2):198-201

2008;**42**(21):8127-8132

Energy. 2018;**125**:319-326

Reviews. 2019;**112**:183-194

2018;**126**:137-155

[120] Al-Jethelah M, Tasnim SH, Mahmud S, Dutta A. Nano-PCM filled energy storage system for solar-thermal applications. Renewable Energy.

Materials Chemistry and Physics.

[117] Panáček A, Kvitek L, Prucek R, Kolář M, Večeřová R, Pizúrová N, et al. Silver colloid nanoparticles: Synthesis, characterization, and their antibacterial

activity. The Journal of Physical

Chemistry B. 2006;**110**(33):16248-16253

[119] Micali F, Milanese M, Colangelo G, de Risi A. Experimental investigation on 4-strokes biodiesel engine cooling system based on nanofluid. Renewable

[121] Said Z, Assad MEH, Hachicha AA, Bellos E, Abdelkareem MA, Alazaizeh DZ, et al. Enhancing the performance of automotive radiators using nanofluids. Renewable and Sustainable Energy

[122] Akilu S, Baheta AT, Said MAM, Minea AA, Sharma K. Properties of glycerol and ethylene glycol mixture based SiO2-CuO/C hybrid nanofluid for enhanced solar energy transport.

[118] Lyon DY, Alvarez PJ. Fullerene water suspension (nC60) exerts antibacterial effects via ROSindependent protein oxidation. Environmental Science & Technology.

2007;**9**(3):479-489

*Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids DOI: http://dx.doi.org/10.5772/intechopen.89904*

[115] Zhang L, Jiang Y, Ding Y, Povey M, York D. Investigation into the antibacterial behaviour of suspensions of ZnO nanoparticles (ZnO nanofluids). Journal of Nanoparticle Research. 2007;**9**(3):479-489

*Engineered Nanomaterials - Health and Safety*

[107] Popa I, Gillies G, Papastavrou G, Borkovec M. Attractive and repulsive electrostatic forces between positively charged latex particles in the presence of anionic linear polyelectrolytes. The Journal of Physical Chemistry B.

[108] Kao M-J, Chang H, Wu Y-Y, Tsung T-T, Lin H-M. Producing aluminumoxide brake nanofluids using plasma charging system. Journal of the Chinese Society of Mechanical Engineers.

[109] Kao M, Lo C, Tsung T, Wu Y, Jwo C, Lin H. Copper-oxide brake nanofluid manufactured using arc-submerged nanoparticle synthesis system. Journal of Alloys and Compounds.

2010;**114**(9):3170-3177

2007a;**28**(2):123-131

2007;**434**:672-674

2012;**2012**:435873

2004;**58**(9):1461-1465

2006;**88**(14):143116

[110] Yu W, Xie H. A review on nanofluids: Preparation, stability mechanisms, and applications. Journal of Nanomaterials.

[111] Tsai C, Chien H, Ding P, Chan B, Luh T, Chen P. Effect of structural character of gold nanoparticles in nanofluid on heat pipe thermal performance. Materials Letters.

[112] Ma H, Wilson C, Borgmeyer B, Park K, Yu Q, Choi S, et al. Effect of nanofluid on the heat transport capability in an oscillating heat pipe. Applied Physics Letters.

[113] Lin Y-H, Kang S-W, Chen H-L. Effect of silver nano-fluid on pulsating heat pipe thermal performance. Applied Thermal Engineering. 2008;**28**(11-12):1312-1317

[114] Vafaei S, Borca-Tasciuc T,

Ajayan P. Effect of nanoparticles on sessile droplet contact angle. Nanotechnology. 2006;**17**(10):2523

Podowski M, Purkayastha A, Ramanath G,

[98] Thirugnanasambandam M, Iniyan S, Goic R. A review of solar thermal technologies. Renewable and Sustainable Energy Reviews.

[99] Kalogirou SA. Solar Energy Engineering: Processes and Systems. United States of America: Academic Press; 2013. ISBN: 9780123972705

[100] Taylor RA, Phelan PE, Otanicar TP, Walker CA, Nguyen M, Trimble S, et al. Applicability of nanofluids in high flux solar collectors. Journal of Renewable and Sustainable Energy.

[101] Badran OO, Abu-Khader MM. Evaluating thermal performance of a single slope solar still. Heat and Mass Transfer. 2007;**43**(10):985-995

[102] Kianifar A, Heris SZ, Mahian O. Exergy and economic analysis of a pyramid-shaped solar water purification

system: Active and passive cases.

[103] Gnanadason MK, Kumar PS, Rajakumar S, Yousuf MS. Effect of nanofluids in a vacuum single basin solar still. International Journal of Advanced Engineering Research and

[104] Nijmeh S, Odeh S, Akash B. Experimental and theoretical study of a single-basin solar sill in Jordan. International Communications in Heat and Mass Transfer. 2005;**32**(3-4):565-572

[105] Shanthi R, Anandan SS, Ramalingam V. Heat transfer

Science. 2012;**16**(2):423-444

enhancement using nanofluids. Thermal

[106] Tzeng S-C, Lin C-W, Huang K. Heat transfer enhancement of nanofluids in rotary blade coupling of four-wheel-drive vehicles. Acta Mechanica. 2005;**179**(1-2):11-23

Energy. 2012;**38**(1):31-36

Studies. 2011;**1**:171-177

2010;**14**(1):312-322

2011;**3**(2):023104

**84**

[116] Jalal R, Goharshadi EK, Abareshi M, Moosavi M, Yousefi A, Nancarrow P. ZnO nanofluids: Green synthesis, characterization, and antibacterial activity. Materials Chemistry and Physics. 2010;**121**(1-2):198-201

[117] Panáček A, Kvitek L, Prucek R, Kolář M, Večeřová R, Pizúrová N, et al. Silver colloid nanoparticles: Synthesis, characterization, and their antibacterial activity. The Journal of Physical Chemistry B. 2006;**110**(33):16248-16253

[118] Lyon DY, Alvarez PJ. Fullerene water suspension (nC60) exerts antibacterial effects via ROSindependent protein oxidation. Environmental Science & Technology. 2008;**42**(21):8127-8132

[119] Micali F, Milanese M, Colangelo G, de Risi A. Experimental investigation on 4-strokes biodiesel engine cooling system based on nanofluid. Renewable Energy. 2018;**125**:319-326

[120] Al-Jethelah M, Tasnim SH, Mahmud S, Dutta A. Nano-PCM filled energy storage system for solar-thermal applications. Renewable Energy. 2018;**126**:137-155

[121] Said Z, Assad MEH, Hachicha AA, Bellos E, Abdelkareem MA, Alazaizeh DZ, et al. Enhancing the performance of automotive radiators using nanofluids. Renewable and Sustainable Energy Reviews. 2019;**112**:183-194

[122] Akilu S, Baheta AT, Said MAM, Minea AA, Sharma K. Properties of glycerol and ethylene glycol mixture based SiO2-CuO/C hybrid nanofluid for enhanced solar energy transport. Solar Energy Materials and Solar Cells. 2018;**179**:118-128

[123] Yao S, Huang X, Song Y, Shen Y, Zhang S. Effects of nanoparticle types and size on boiling feat transfer performance under different pressures. AIP Advances. 2018;**8**(2):025005

**87**

**Chapter 5**

**Abstract**

chemistry.

**1. Introduction**

as adsorbents.

*and Nazish Huma Khan*

zinc oxide and magnesium oxide

size, diameter and layer thickness [1–5].

Preparation of Nano-Particles and

Their Applications in Adsorption

The nano-technologies and nano-materials draw incredible consideration in recent years. Nano-particles are the particles having size ranging from 1 to 100 nm. The nano-particles are usually categorized into different classes, and their classification is based on size, shape, material production, and dimension. They show superior properties, i.e., enhanced reactivity, high BET surface area, sensitiveness, and steadiness as compared to their bulk materials. In this chapter, different approaches of synthesizing nano-particles, including sol gel, chemical vapor deposition, and biosynthesis are talked over. In the treatment of wastewater, nano-particles offer a possibility for effective adsorption of contaminants organic as well as inorganic. This chapter presents an overview on nano-particles, their types, characteristics, synthetic approaches, and applications in the field of surface

**Keywords:** nano-particles, adsorption, sol–gel, chemical vapor deposition, biosynthesis, carbon nano-tubes, mechanical milling, nano-lithography, laser ablation, iron nano-particles, manganese oxide nano-particles,

This chapter consists of three main sections. The first section gives an overview about the introduction of nano-particles. The next section is about the synthesis of nanoparticles and the last section describes the use of nanoparticles

The preface "nano" is known for nineteenth century for its ever-increasing applications in various fields of science. A few nano-containing terms that are found in the record (usually in scientific reports and books) are nano-materials, nano-chemistry, nano-science or nanotechnology. The preface nano comes from a Latin nanos meaning dwarf that means extremely small. According to units system working internationally, it is used to represent a reduction factor of 109 times. Consequently, the nano-materials are usually dignified in nano-meters (1 nm is equivalent to 10–9 m) and it comprises systems having size less than macroscopic measurements and greater than molecular ones (mostly >1 nm and <100 nm) at least in one spatial dimension. This characteristic scale might be used for a particle

*Tooba Saeed, Abdul Naeem, Tahira Mahmood* 

#### **Chapter 5**

## Preparation of Nano-Particles and Their Applications in Adsorption

*Tooba Saeed, Abdul Naeem, Tahira Mahmood and Nazish Huma Khan*

#### **Abstract**

The nano-technologies and nano-materials draw incredible consideration in recent years. Nano-particles are the particles having size ranging from 1 to 100 nm. The nano-particles are usually categorized into different classes, and their classification is based on size, shape, material production, and dimension. They show superior properties, i.e., enhanced reactivity, high BET surface area, sensitiveness, and steadiness as compared to their bulk materials. In this chapter, different approaches of synthesizing nano-particles, including sol gel, chemical vapor deposition, and biosynthesis are talked over. In the treatment of wastewater, nano-particles offer a possibility for effective adsorption of contaminants organic as well as inorganic. This chapter presents an overview on nano-particles, their types, characteristics, synthetic approaches, and applications in the field of surface chemistry.

**Keywords:** nano-particles, adsorption, sol–gel, chemical vapor deposition, biosynthesis, carbon nano-tubes, mechanical milling, nano-lithography, laser ablation, iron nano-particles, manganese oxide nano-particles, zinc oxide and magnesium oxide

#### **1. Introduction**

This chapter consists of three main sections. The first section gives an overview about the introduction of nano-particles. The next section is about the synthesis of nanoparticles and the last section describes the use of nanoparticles as adsorbents.

The preface "nano" is known for nineteenth century for its ever-increasing applications in various fields of science. A few nano-containing terms that are found in the record (usually in scientific reports and books) are nano-materials, nano-chemistry, nano-science or nanotechnology. The preface nano comes from a Latin nanos meaning dwarf that means extremely small. According to units system working internationally, it is used to represent a reduction factor of 109 times. Consequently, the nano-materials are usually dignified in nano-meters (1 nm is equivalent to 10–9 m) and it comprises systems having size less than macroscopic measurements and greater than molecular ones (mostly >1 nm and <100 nm) at least in one spatial dimension. This characteristic scale might be used for a particle size, diameter and layer thickness [1–5].

#### **1.1 Classification of nano-materials**

The nano-materials are different in structure, size and shape. They can be of various shapes like rod, globular, conical, hollow, coiled, plane, cylindrical and asymmetrical, while some are crystalline or amorphous.

Nano-materials are generally classified into nano-emulsions, nano-clays and nano-particles. Nano-particles are present as nano-composites or nano-structures. These nano-structures are made from basic units or blocks having small dimensionality i.e. zero, one, two and three dimensions. In zero dimensional nano-particles, the moment of electrons is cramped in all three dimensions, e.g. quantum dots. If electrons can move freely in x-direction only, they are one dimensional nanoparticles e.g. quantum wires. Whereas, in two dimensional thin films and three dimensional nano-structured materials, free electrons can move freely in x, y and x, y, z directions respectively.

Based on material production and role in sorption process, nano-particles can also be categorized into organic, mixed oxide nano-structures, magnetic, inorganic (metallic) and carbon based nano-particles. Organic nano-particles are self-assembled, three dimensional fabricated by synthetic and natural organic molecules, i.e. protein masses, milk suspension and lipid bulks etc. Commonly known organic nanoparticles are micelles, dendrimers, ferritin and liposomes. Inorganic nanoparticles usually are manufactured from inorganic salt precipitations. They are non-carbon containing particles and their most common examples are metal and metal oxide particles. Carbon based nano-particles are manufactured entirely from carbon e.g. graphene, fullerenes, carbon nano-tubes, carbon nano-fibers, carbon black and sometimes activated carbon (**Figure 1**) [6–10].

In nano-materials (especially nano-particles) molecules and atoms act differently and reveal inimitable physical, chemical and electronic properties. These properties are different from their bulk counterparts and sometimes the same kind of nano-particles can show diverse characters. Physical properties of nano-particles

**89**

**Figure 2.**

*Applications of nano-particles in different fields [20].*

*Preparation of Nano-Particles and Their Applications in Adsorption*

include absorption, reflection, light dispersion, color of nano-particles, hydrophobicity, hydro-philicity, suspension and dispersion. When layered onto a surface or in the form of solution their absorption and reflection properties make them a perfect choice for different fields. They also show outstanding chemical properties, i.e. anti-destructive, oxidation, reduction, flammability, sensitivity and stability towards humidity, atmosphere, heat, light and dis-infection, non-toxicity, biodegradability, anti-bacterial and fungal properties. These properties also enable them ideal materials for environmental and biomedical applications. Nano-particles also exhibit mechanical properties like elasticity, ductility, flexibility, tensile strength and electrical properties including semi-conductivity, conductivity and resistivity which have directed a route for them to be used in renewable energy applications. These distinctive and inimitable properties of nano-particles make them perfect

and formidable for amazing and interesting applications in physical science, material science, agriculture, food, engineering, industrial and biomedical sciences

These applications encompass them to be used in electronic, drug delivery, optical, mechanics, catalysis, bio-encapsulation and wastewater treatment especially adsorption [4–15]. Besides all these properties, nano-particles have some toxic effects for aquatic and human health. As they have small size, they can easily enter through the skin of organisms and consequently enter into the body fluid. Furthermore, nano-particles used in sun screens can absorb deep inside and become toxic to the skin, bones and liver cells. Their greater surface area often makes them more sensitive, explosive and reactive. Inhaling directly in the environment of nano-particles can adversely affect the function of lungs especially in human being. However, highlighting the health issues caused by nano-particles, does not mean to ignore their extraordinary importance in technology, industries

It is important to mention that water is one among the basic necessities of every organism. From total water present on earth, only 0.01% portion is available for human [19, 20]. Shortage of drinking water is increasing day by day due to demoli-

*DOI: http://dx.doi.org/10.5772/intechopen.89534*

(**Figure 2**).

and environment [16–18].

tion of water means [21].

**Figure 1.** *Classification of nano-materials.*

#### *Preparation of Nano-Particles and Their Applications in Adsorption DOI: http://dx.doi.org/10.5772/intechopen.89534*

*Engineered Nanomaterials - Health and Safety*

**1.1 Classification of nano-materials**

directions respectively.

asymmetrical, while some are crystalline or amorphous.

black and sometimes activated carbon (**Figure 1**) [6–10].

The nano-materials are different in structure, size and shape. They can be of various shapes like rod, globular, conical, hollow, coiled, plane, cylindrical and

Nano-materials are generally classified into nano-emulsions, nano-clays and nano-particles. Nano-particles are present as nano-composites or nano-structures. These nano-structures are made from basic units or blocks having small dimensionality i.e. zero, one, two and three dimensions. In zero dimensional nano-particles, the moment of electrons is cramped in all three dimensions, e.g. quantum dots. If electrons can move freely in x-direction only, they are one dimensional nanoparticles e.g. quantum wires. Whereas, in two dimensional thin films and three dimensional nano-structured materials, free electrons can move freely in x, y and x, y, z

Based on material production and role in sorption process, nano-particles can also be categorized into organic, mixed oxide nano-structures, magnetic, inorganic (metallic) and carbon based nano-particles. Organic nano-particles are self-assembled, three dimensional fabricated by synthetic and natural organic molecules, i.e. protein masses, milk suspension and lipid bulks etc. Commonly known organic nanoparticles are micelles, dendrimers, ferritin and liposomes. Inorganic nanoparticles usually are manufactured from inorganic salt precipitations. They are non-carbon containing particles and their most common examples are metal and metal oxide particles. Carbon based nano-particles are manufactured entirely from carbon e.g. graphene, fullerenes, carbon nano-tubes, carbon nano-fibers, carbon

In nano-materials (especially nano-particles) molecules and atoms act differently and reveal inimitable physical, chemical and electronic properties. These properties are different from their bulk counterparts and sometimes the same kind of nano-particles can show diverse characters. Physical properties of nano-particles

**88**

**Figure 1.**

*Classification of nano-materials.*

include absorption, reflection, light dispersion, color of nano-particles, hydrophobicity, hydro-philicity, suspension and dispersion. When layered onto a surface or in the form of solution their absorption and reflection properties make them a perfect choice for different fields. They also show outstanding chemical properties, i.e. anti-destructive, oxidation, reduction, flammability, sensitivity and stability towards humidity, atmosphere, heat, light and dis-infection, non-toxicity, biodegradability, anti-bacterial and fungal properties. These properties also enable them ideal materials for environmental and biomedical applications. Nano-particles also exhibit mechanical properties like elasticity, ductility, flexibility, tensile strength and electrical properties including semi-conductivity, conductivity and resistivity which have directed a route for them to be used in renewable energy applications.

These distinctive and inimitable properties of nano-particles make them perfect and formidable for amazing and interesting applications in physical science, material science, agriculture, food, engineering, industrial and biomedical sciences (**Figure 2**).

These applications encompass them to be used in electronic, drug delivery, optical, mechanics, catalysis, bio-encapsulation and wastewater treatment especially adsorption [4–15]. Besides all these properties, nano-particles have some toxic effects for aquatic and human health. As they have small size, they can easily enter through the skin of organisms and consequently enter into the body fluid. Furthermore, nano-particles used in sun screens can absorb deep inside and become toxic to the skin, bones and liver cells. Their greater surface area often makes them more sensitive, explosive and reactive. Inhaling directly in the environment of nano-particles can adversely affect the function of lungs especially in human being. However, highlighting the health issues caused by nano-particles, does not mean to ignore their extraordinary importance in technology, industries and environment [16–18].

It is important to mention that water is one among the basic necessities of every organism. From total water present on earth, only 0.01% portion is available for human [19, 20]. Shortage of drinking water is increasing day by day due to demolition of water means [21].

**Figure 2.**

*Applications of nano-particles in different fields [20].*

The main sources of water contamination are agricultural, industrial and domestic effluents. Industries can help on the one hand in the development of economy, whereas, on the other hand, they are mainly responsible for various environmental issues i.e. water, air and soil pollution. Drinking water containing agricultural and industrial effluents cause different diseases such as, cancer, eye irritation, dermatitis, cell damage and dysfunction of kidney, respiratory and reproductive system even in a very insignificant quantity. Hence, treatment methods for drinking as well as wastewater are one of the most important requirements for emerging and growing health and economy. Various techniques have been used for decontamination of pollutants from industrial wastewater, including reverse-osmosis, ion-exchange, chemical oxidation, flocculation or coagulation and precipitation. Each technique has its individual disadvantages as they are energy dependent, economically as well as technically not sound and achievable. Literature exhibited that from all these treatment techniques, adsorption is one of the most effective technique for water decontamination. Adsorption is simple, adaptable, highly potential, efficient and recyclable technique [22, 23]. A range of effective, low-cost and environment friendly nano-materials with outstanding properties have been developed for prospective applications in decontamination of industrial effluents, surface, ground and drinking water. Literature also revealed that nanoparticles behave as an ideal adsorbent as they are environmentally benign, selective, efficient, recyclable, high surface area and maximum adsorption capacity even at a very low concentration [24–26].

The recent progress related to the different aspects of adsorption using nanoparticles have described in several reviews and book chapters. This chapter focuses on the various techniques used for preparation of nano-particles and their applications in the field of adsorption.

#### **2. Preparation of nano-particles**

The nano-particles can be prepared by various processes divided into i.e. bottom up and top down techniques. Bottom up methods include the reduction of material components up to the atomic level and then with further self-assembly lead to the formation of nano-particles. However, during self-assembly, the physical forces functioning at nano-scale are used to connect basic units into macro structures. Pyrolysis, bio-synthesis, sole gel, spinning and chemical vapor deposition are most extensively used methods fall in this approach [6, 27]. Whereas, top down techniques including sputtering, laser ablation, nano-lithography, mechanical milling and thermal decomposition, starting with a pattern produced on a higher scale, then compacted to nanoscale. Both of these techniques are contradictory and schematically represented in **Figure 3**.

#### **2.1 Bottom up technique**

#### *2.1.1 Sol gel*

The sol is a colloid where the aggregates of fine particle are distributed in liquid phase. They are larger in size ranging from 1 nm to 1 μm than nano-particles. Whereas, solid macromolecules immersed in a solvent, called as gel. Sol gel is one of the simplest and, most commonly used method for the synthesis of nano-particles. It is a chemical method which comprises of a solution working as a precursor for an assimilated system of distinct particles. In this method, metal oxides, metal chlorides and alkoxysilanes (typically tetramethoxy and ethoxysilanes) are most

**91**

during this process.

**Figure 3.**

*2.1.2 Chemical-vapor deposition (CVD)*

*Schematic representation of bottom up and top down techniques.*

gaseous by-products [8, 31, 32].

*2.1.3 Biosynthesis*

cal applications [33, 34].

*Preparation of Nano-Particles and Their Applications in Adsorption*

commonly used as precursors. The precursor is mixed by means of mixing, quivering sonicating or stirring and is then spread in second liquid which form a solid–liquid phase. Catalyst is commonly used to start the reaction and to control the pH of the system. Sedimentation, filtration and centrifugation are the typical methods used for phase separation to get nano-particles and then the sample is dried to remove moistness. The main advantages of this process are to attain uniform nano-structures even at a very low temperature, having controlled chemical composition and purity [6, 27–30]. This process is not easily scalable having different drying steps involved as well as it is difficult to control synthesis

In this method of preparation, substrate is coated with a thin film of gaseous reactants. The gas molecules are combined at ambient temperature in a reaction chamber to carry out deposition. Upon heating substrate comes in vicinity of combined gas where a chemical reaction occurs and a thin film is formed on the surface of substrate. This thin film can be recovered and reused for different applications. The basic influencing factor in this method is the temperature of the substrate. The nanoparticles achieved through this method are highly pure, uniform in size, strong and have high mechanical stability. The disadvantages of CVD include the use of special equipment as well as the high toxicity of the

Biosynthesis is one of the inexpensive, green, safe, decomposable and environment friendly methods used for the synthesis of nano-particles. In this method bacterium, fungi and plant extracts are used in conjunction with precursor for bio-reduction and capping functions rather than conventional chemicals. This method has its distinctive and enriched properties that find its approaches in medi-

*DOI: http://dx.doi.org/10.5772/intechopen.89534*

*Preparation of Nano-Particles and Their Applications in Adsorption DOI: http://dx.doi.org/10.5772/intechopen.89534*

#### **Figure 3.**

*Engineered Nanomaterials - Health and Safety*

very low concentration [24–26].

tions in the field of adsorption.

**2. Preparation of nano-particles**

schematically represented in **Figure 3**.

**2.1 Bottom up technique**

*2.1.1 Sol gel*

The main sources of water contamination are agricultural, industrial and domestic effluents. Industries can help on the one hand in the development of economy, whereas, on the other hand, they are mainly responsible for various environmental issues i.e. water, air and soil pollution. Drinking water containing agricultural and industrial effluents cause different diseases such as, cancer, eye irritation, dermatitis, cell damage and dysfunction of kidney, respiratory and reproductive system even in a very insignificant quantity. Hence, treatment methods for drinking as well as wastewater are one of the most important requirements for emerging and growing health and economy. Various techniques have been used for decontamination of pollutants from industrial wastewater, including reverse-osmosis, ion-exchange, chemical oxidation, flocculation or coagulation and precipitation. Each technique has its individual disadvantages as they are energy dependent, economically as well as technically not sound and achievable. Literature exhibited that from all these treatment techniques, adsorption is one of the most effective technique for water decontamination. Adsorption is simple, adaptable, highly potential, efficient and recyclable technique [22, 23]. A range of effective, low-cost and environment friendly nano-materials with outstanding properties have been developed for prospective applications in decontamination of industrial effluents, surface, ground and drinking water. Literature also revealed that nanoparticles behave as an ideal adsorbent as they are environmentally benign, selective, efficient, recyclable, high surface area and maximum adsorption capacity even at a

The recent progress related to the different aspects of adsorption using nanoparticles have described in several reviews and book chapters. This chapter focuses on the various techniques used for preparation of nano-particles and their applica-

The nano-particles can be prepared by various processes divided into i.e. bottom up and top down techniques. Bottom up methods include the reduction of material components up to the atomic level and then with further self-assembly lead to the formation of nano-particles. However, during self-assembly, the physical forces functioning at nano-scale are used to connect basic units into macro structures. Pyrolysis, bio-synthesis, sole gel, spinning and chemical vapor deposition are most extensively used methods fall in this approach [6, 27]. Whereas, top down techniques including sputtering, laser ablation, nano-lithography, mechanical milling and thermal decomposition, starting with a pattern produced on a higher scale, then compacted to nanoscale. Both of these techniques are contradictory and

The sol is a colloid where the aggregates of fine particle are distributed in liquid phase. They are larger in size ranging from 1 nm to 1 μm than nano-particles. Whereas, solid macromolecules immersed in a solvent, called as gel. Sol gel is one of the simplest and, most commonly used method for the synthesis of nano-particles. It is a chemical method which comprises of a solution working as a precursor for an assimilated system of distinct particles. In this method, metal oxides, metal chlorides and alkoxysilanes (typically tetramethoxy and ethoxysilanes) are most

**90**

*Schematic representation of bottom up and top down techniques.*

commonly used as precursors. The precursor is mixed by means of mixing, quivering sonicating or stirring and is then spread in second liquid which form a solid–liquid phase. Catalyst is commonly used to start the reaction and to control the pH of the system. Sedimentation, filtration and centrifugation are the typical methods used for phase separation to get nano-particles and then the sample is dried to remove moistness. The main advantages of this process are to attain uniform nano-structures even at a very low temperature, having controlled chemical composition and purity [6, 27–30]. This process is not easily scalable having different drying steps involved as well as it is difficult to control synthesis during this process.

#### *2.1.2 Chemical-vapor deposition (CVD)*

In this method of preparation, substrate is coated with a thin film of gaseous reactants. The gas molecules are combined at ambient temperature in a reaction chamber to carry out deposition. Upon heating substrate comes in vicinity of combined gas where a chemical reaction occurs and a thin film is formed on the surface of substrate. This thin film can be recovered and reused for different applications. The basic influencing factor in this method is the temperature of the substrate. The nanoparticles achieved through this method are highly pure, uniform in size, strong and have high mechanical stability. The disadvantages of CVD include the use of special equipment as well as the high toxicity of the gaseous by-products [8, 31, 32].

#### *2.1.3 Biosynthesis*

Biosynthesis is one of the inexpensive, green, safe, decomposable and environment friendly methods used for the synthesis of nano-particles. In this method bacterium, fungi and plant extracts are used in conjunction with precursor for bio-reduction and capping functions rather than conventional chemicals. This method has its distinctive and enriched properties that find its approaches in medical applications [33, 34].

#### *2.1.4 Pyrolysis*

Pyrolysis is the method used in industries to prepare nan-particles on large scale. In this method, precursor used can be liquid or vapor. A furnace is used in order to burn the precursor. Precursor is added to the furnace through a small opening where flame is applied to burn it. [13]. Nano-particles are collected by the gases produced as by product. Pyrolysis is an effective method for nanoparticle preparation due to its simplicity, high product yield and sensitiveness [35, 36].

#### **2.2 Top down techniques**

#### *2.2.1 Mechanical milling*

One of the most widely used top down techniques to produce nano-particles is mechanical milling. In this method various elements are milled under an inert atmosphere and during this process particles are milled and post annealed. The influencing factor in this method is plastic distortion which end up with particle size, breakage that ends up in particle size, and cold-soldering that ends up to increased particle size [37–39].

#### *2.2.2 Nano-lithography*

Nanolithography is the investigation of manufacturing nano-scale structures of one dimension at least, with size ranging from 1 to 100 nm. There are different nano-lithographic forms, for example optical, electron-pillar, multiphoton, nanoimprint and filtering test lithography. Mostly lithography is the way towards printing a required shape or structure of a light sensitive material, which specifically evacuates a bit of material to make the ideal shape and structure. The primary advantage of nanolithography is to create a bunch from a solitary nano-particle with desired shape and size [40–42]. A sophisticated equipment is required in this method which is cost effective.

#### *2.2.3 Laser-ablation*

Laser-ablation is a typical method for the preparation of nano-particles from various solvents in solution. A metal immersed in a liquid solution is irradiated by the laser beam, resulting in the formation of plasma crest that yields into nano-particles. In this process, a chemical reduction of metals occurs to produce inorganic (metal based) nano-particles. As laser ablation gives a steady synthesis of nano-particles in natural solvents and water that does not require any balancing agent or synthetic substance. It is a 'green' process and its setup is shown in **Figure 4** [43–45].

#### *2.2.4 Thermal decomposition*

In this method heat is applied to decompose the chemical bonds of the compound. It is an endothermic chemical process where the nano-particles are synthesized by rotting a metal at a precise temperature called as decomposition temperature. As a result of this decomposition secondary products are also produced. This method is useful for the preparation of metal oxide and carbon based nano-particles [46, 47].

**93**

*Preparation of Nano-Particles and Their Applications in Adsorption*

**3. Applications of nano-particles as adsorbent**

treatment [48–50].

**Figure 4.**

*Laser ablation setup [43].*

cal bonding [51–54].

Now a days, one of the foremost problems that is facing by the world is accessibility of clean drinking water. Demand for fresh and clean water is increasing day by day due to increasing population. In developing and industrialized countries, clean water deficiency is intensified by human as well as by the industrial effluents (metals and dyes). These effluents are directly discharged into water bodies and contaminate them. As described in introduction part of this chapter, sorption is declared to be one of the best and suitable methods for wastewater

The sorption method is a surface phenomenon during which sorbate is gathered on the sorbent surface. When adsorbate molecules from solution come to the vicinity of adsorbent surface, then some of the molecules adsorb onto the sorbent surface by intermolecular forces of attraction between surfaces of adsorbent and adsorbate molecules. The particular nature of interaction can be determined by the type of species concerned. However, the sorption method is usually classified as physi-sorption where the sorbate bound on the sorbent surface through valence or electrostatic bonding and chemi-sorption where molecule attached through chemi-

Nano-particles have a high specific surface area, sorption active sites, solubility, efficiency and fractal dimension, short intra-particle diffusion distance, well defined chemical composition, small particle size and tunable pore size as compare to the their bulk counterparts that are responsible for their valuable features for effective sorption especially chemical activity and fine grain size. The high surface area and high sorption active site in nano-particles are due to high surface-energy and size dependent surface structure at nano-scale. The nano-particles have the highest efficiency towards sorption of organic and inorganic pollutants and their selectivity towards contaminants can be increased by functionalizing the surface of nano-particles. Iron oxide, titanium dioxide, manganese dioxide, silica nanoparticles, alumina, zinc oxide, dicalcium phosphate, copper, silver, maghemite, gold nano-particles, etc. are discovered as cheap, efficient, easy to synthesize and

*DOI: http://dx.doi.org/10.5772/intechopen.89534*

*Preparation of Nano-Particles and Their Applications in Adsorption DOI: http://dx.doi.org/10.5772/intechopen.89534*

**Figure 4.** *Laser ablation setup [43].*

*Engineered Nanomaterials - Health and Safety*

Pyrolysis is the method used in industries to prepare nan-particles on large scale. In this method, precursor used can be liquid or vapor. A furnace is used in order to burn the precursor. Precursor is added to the furnace through a small opening where flame is applied to burn it. [13]. Nano-particles are collected by the gases produced as by product. Pyrolysis is an effective method for nanoparticle preparation due to its simplicity, high product yield and sensitiveness

One of the most widely used top down techniques to produce nano-particles is mechanical milling. In this method various elements are milled under an inert atmosphere and during this process particles are milled and post annealed. The influencing factor in this method is plastic distortion which end up with particle size, breakage that ends up in particle size, and cold-soldering that ends up to

Nanolithography is the investigation of manufacturing nano-scale structures of one dimension at least, with size ranging from 1 to 100 nm. There are different nano-lithographic forms, for example optical, electron-pillar, multiphoton, nanoimprint and filtering test lithography. Mostly lithography is the way towards printing a required shape or structure of a light sensitive material, which specifically evacuates a bit of material to make the ideal shape and structure. The primary advantage of nanolithography is to create a bunch from a solitary nano-particle with desired shape and size [40–42]. A sophisticated equipment is required in this

Laser-ablation is a typical method for the preparation of nano-particles from various solvents in solution. A metal immersed in a liquid solution is irradiated by the laser beam, resulting in the formation of plasma crest that yields into nano-particles. In this process, a chemical reduction of metals occurs to produce inorganic (metal based) nano-particles. As laser ablation gives a steady synthesis of nano-particles in natural solvents and water that does not require any balancing agent or synthetic substance. It is a 'green' process and its setup is shown in

In this method heat is applied to decompose the chemical bonds of the compound. It is an endothermic chemical process where the nano-particles are synthesized by rotting a metal at a precise temperature called as decomposition temperature. As a result of this decomposition secondary products are also produced. This method is useful for the preparation of metal oxide and carbon based

*2.1.4 Pyrolysis*

[35, 36].

**2.2 Top down techniques**

increased particle size [37–39].

method which is cost effective.

*2.2.3 Laser-ablation*

**Figure 4** [43–45].

*2.2.4 Thermal decomposition*

nano-particles [46, 47].

*2.2.2 Nano-lithography*

*2.2.1 Mechanical milling*

**92**

#### **3. Applications of nano-particles as adsorbent**

Now a days, one of the foremost problems that is facing by the world is accessibility of clean drinking water. Demand for fresh and clean water is increasing day by day due to increasing population. In developing and industrialized countries, clean water deficiency is intensified by human as well as by the industrial effluents (metals and dyes). These effluents are directly discharged into water bodies and contaminate them. As described in introduction part of this chapter, sorption is declared to be one of the best and suitable methods for wastewater treatment [48–50].

The sorption method is a surface phenomenon during which sorbate is gathered on the sorbent surface. When adsorbate molecules from solution come to the vicinity of adsorbent surface, then some of the molecules adsorb onto the sorbent surface by intermolecular forces of attraction between surfaces of adsorbent and adsorbate molecules. The particular nature of interaction can be determined by the type of species concerned. However, the sorption method is usually classified as physi-sorption where the sorbate bound on the sorbent surface through valence or electrostatic bonding and chemi-sorption where molecule attached through chemical bonding [51–54].

Nano-particles have a high specific surface area, sorption active sites, solubility, efficiency and fractal dimension, short intra-particle diffusion distance, well defined chemical composition, small particle size and tunable pore size as compare to the their bulk counterparts that are responsible for their valuable features for effective sorption especially chemical activity and fine grain size. The high surface area and high sorption active site in nano-particles are due to high surface-energy and size dependent surface structure at nano-scale. The nano-particles have the highest efficiency towards sorption of organic and inorganic pollutants and their selectivity towards contaminants can be increased by functionalizing the surface of nano-particles. Iron oxide, titanium dioxide, manganese dioxide, silica nanoparticles, alumina, zinc oxide, dicalcium phosphate, copper, silver, maghemite, gold nano-particles, etc. are discovered as cheap, efficient, easy to synthesize and

environment friendly sorbents for the removal of pollutants. Among nano-particles (metal oxides), the magnetic nano-particles have acquired a substantial importance due to their interesting magnetic properties i.e. super para-magnetism, strong reaction even at minor applied magnetic field [6, 12, 55, 56].

Moreover, a recent improvement on carboniferous and siliceous nano-materials enclosed nano-sheets, nano-tubes and nano-particles of carbon and silicon declared as efficient adsorbents for sorption of metals and dyes from wastewater. Some oxides and carbon based nanomaterials are discussed below [55–57].

#### **3.1 Iron nano-particles**

Iron based nano-particles are most commonly used adsorbents for the removal of toxic materials from aqueous solutions. These nano-particles are declared as most efficient, cost effective and ecofriendly sorbent with less chance for the production of secondary contaminants. The adsorption process by iron oxide nano-particles is affected by pH, temperature, adsorbent dosage and equilibrium time. Modification of these materials increased their surface properties for the removal of metals, i.e. cadmium(II), lead(II), copper(II), chromium(II), nickel(II), arsenic(III) and anionic and cationic dyes [58–60].

#### **3.2 Manganese oxide nano-particles**

Manganese oxide nano-particles have a high specific surface area which makes them effective adsorbent for the removal of heavy metals i.e. arsenic(III), lead(II), cadmium(II) and ionic dyes. Manganese oxide nano-particles can also be modified into hydrous manganese oxide, nano-porous and nano-tunnel manganese oxide to improve their surface area and porosity for excellent adsorption [61, 62].

#### **3.3 Zinc oxide**

These are porous micro nano-structure with high Brunauer-Emmett-Teller (BET) surface area. Most widely used nano-sorbents of zinc oxide are nanoassembled, nano-sheets, nano-rods, nano-plates and micro-spheres for competent removal of dyes and inorganic pollutants from aqueous phase. Whereas, micro-porous nano assemblies of zinc oxide display maximum potential for the removal of lead(II), arsenic(III) and mercury(II) because of their electropositive nature [63–65].

#### **3.4 Magnesium oxide**

The sorption capacity of the magnesium oxide nano-particles is much greater than its bulk counterpart. Their micro-spheres are innovative structure, with increased sorption capacity for the sorption of heavy metals. Various modification of magnesium oxide nano-particles i.e. nano-rods, nano-tubes, nano-wires has been reported as improved sorption affinity towards metals and organic effluents [66–68].

#### **3.5 Carbon nano-tubes**

They are the most widely used material for the sorption of heavy metals as well as organic dyes from aqueous media. Though, they have meager dispersal capacity, very small size of particles and separation complications are some difficulties for using carbon nano-tubes as sorbents. Whereas, these difficulties can be overawed

**95**

*Preparation of Nano-Particles and Their Applications in Adsorption*

efficiently as compare to unmodified material [22, 69, 70].

their proficiency and environmentally benign property.

sary support and facilities to carry out this study.

\*, Abdul Naeem1

provided the original work is properly cited.

\*Address all correspondence to: khantooba590@gmail.com

by modifying carbon nano-tubes into multi walled carbon nano-tubes. Literature revealed that the multi walled nano tubes and alumina supported carbon nanotubes, more competently removed metals such as Mn(II), Cu(II) and Pb(II) more

Nano-technology is refining our everyday life by increasing the proficiency and purity of many substances. As described in this chapter, there are different techniques for the synthesis of nano-particles, but laser ablation chemical vapor deposition, nano-lithography, biosynthesis, mechanical milling, and sol–gel are the most suitable techniques because they are less time consuming methods. Nano-particles with inimitable chemical and physical characteristics, have a remarkable prospective for the adsorption of contaminant but still their applications for wastewater treatment are inadequate. However, nanoparticles have pronounced future due to

The authors would like to convey their gratefulness to National Centre of Excellence in Physical Chemistry, University of Peshawar for providing us neces-

, Tahira Mahmood1

1 National Centre of Excellence in Physical Chemistry, University of Peshawar,

2 Department of Environmental Sciences, University of Sawabi, Sawabi, Pakistan

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Nazish Huma Khan2

*DOI: http://dx.doi.org/10.5772/intechopen.89534*

**4. Conclusion**

**Acknowledgements**

**Author details**

Peshawar, Pakistan

Tooba Saeed1

by modifying carbon nano-tubes into multi walled carbon nano-tubes. Literature revealed that the multi walled nano tubes and alumina supported carbon nanotubes, more competently removed metals such as Mn(II), Cu(II) and Pb(II) more efficiently as compare to unmodified material [22, 69, 70].

## **4. Conclusion**

*Engineered Nanomaterials - Health and Safety*

**3.1 Iron nano-particles**

**3.3 Zinc oxide**

positive nature [63–65].

**3.4 Magnesium oxide**

effluents [66–68].

**3.5 Carbon nano-tubes**

anionic and cationic dyes [58–60].

**3.2 Manganese oxide nano-particles**

tion even at minor applied magnetic field [6, 12, 55, 56].

oxides and carbon based nanomaterials are discussed below [55–57].

environment friendly sorbents for the removal of pollutants. Among nano-particles (metal oxides), the magnetic nano-particles have acquired a substantial importance due to their interesting magnetic properties i.e. super para-magnetism, strong reac-

Moreover, a recent improvement on carboniferous and siliceous nano-materials enclosed nano-sheets, nano-tubes and nano-particles of carbon and silicon declared as efficient adsorbents for sorption of metals and dyes from wastewater. Some

Iron based nano-particles are most commonly used adsorbents for the removal of toxic materials from aqueous solutions. These nano-particles are declared as most efficient, cost effective and ecofriendly sorbent with less chance for the production of secondary contaminants. The adsorption process by iron oxide nano-particles is affected by pH, temperature, adsorbent dosage and equilibrium time. Modification of these materials increased their surface properties for the removal of metals, i.e. cadmium(II), lead(II), copper(II), chromium(II), nickel(II), arsenic(III) and

Manganese oxide nano-particles have a high specific surface area which makes them effective adsorbent for the removal of heavy metals i.e. arsenic(III), lead(II), cadmium(II) and ionic dyes. Manganese oxide nano-particles can also be modified into hydrous manganese oxide, nano-porous and nano-tunnel manganese oxide to

These are porous micro nano-structure with high Brunauer-Emmett-Teller (BET) surface area. Most widely used nano-sorbents of zinc oxide are nanoassembled, nano-sheets, nano-rods, nano-plates and micro-spheres for competent removal of dyes and inorganic pollutants from aqueous phase. Whereas, micro-porous nano assemblies of zinc oxide display maximum potential for the removal of lead(II), arsenic(III) and mercury(II) because of their electro-

The sorption capacity of the magnesium oxide nano-particles is much greater than its bulk counterpart. Their micro-spheres are innovative structure, with increased sorption capacity for the sorption of heavy metals. Various modification of magnesium oxide nano-particles i.e. nano-rods, nano-tubes, nano-wires has been reported as improved sorption affinity towards metals and organic

They are the most widely used material for the sorption of heavy metals as well as organic dyes from aqueous media. Though, they have meager dispersal capacity, very small size of particles and separation complications are some difficulties for using carbon nano-tubes as sorbents. Whereas, these difficulties can be overawed

improve their surface area and porosity for excellent adsorption [61, 62].

**94**

Nano-technology is refining our everyday life by increasing the proficiency and purity of many substances. As described in this chapter, there are different techniques for the synthesis of nano-particles, but laser ablation chemical vapor deposition, nano-lithography, biosynthesis, mechanical milling, and sol–gel are the most suitable techniques because they are less time consuming methods. Nano-particles with inimitable chemical and physical characteristics, have a remarkable prospective for the adsorption of contaminant but still their applications for wastewater treatment are inadequate. However, nanoparticles have pronounced future due to their proficiency and environmentally benign property.

## **Acknowledgements**

The authors would like to convey their gratefulness to National Centre of Excellence in Physical Chemistry, University of Peshawar for providing us necessary support and facilities to carry out this study.

## **Author details**

Tooba Saeed1 \*, Abdul Naeem1 , Tahira Mahmood1 and Nazish Huma Khan2

1 National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar, Pakistan

2 Department of Environmental Sciences, University of Sawabi, Sawabi, Pakistan

\*Address all correspondence to: khantooba590@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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**101**

Section 2

Biological Properties

of Nanoparticles

Section 2
