**2. Classifications of carbon and carbon-based nanomaterials**

Carbon have tendency to polymerize into the large molecular weight compounds with long chains due to its unique electronic construction and the smaller size in comparison of group IV that makes it capable of linking with other elements. As it contains four electrons in the valence layers, carbon can easily form covalent bonds with both metals and non-metals. Due to this property, carbon-based compounds can exist in diverse molecular forms, and same type of atoms can be arranged in the different shapes, with different properties known as allotropes. Graphite and diamond are two known natural occurring allotropes of carbon found in the ecology and formed other multiple allotropes of carbon from natural carbon sources for the different purposes. Furthermore, with the knowledge of top down and bottom up approaches of nanotechnology, a new family of carbon nanomaterials as wonder materials is introduced. In recent past years, the different types of carbon nanomaterials have been experimentally tested and successfully developed as advance materials in many engineering applications. In general, carbon nanomaterials exist in between 1 and 100 nm size range; therefore, the unique properties of carbon nanomaterials like good electrical, ionic conductivity, high mechanical and thermal stability at the nanoscale compared with other materials are exceptional and competent for many engineering applications [16]. Carbon nanomaterials are classified further based on their shape and geometrical structures, till dates different forms of carbon nanomaterials that are existing; horn-shaped as nanohorns, tube-shaped as carbon nanotube (CNT), ellipsoidal spherical shape carbon nanospheres (fullerenes), and zero-dimension dots exhibited quantum character as carbon quantum dots (CQDs). Because of excellent properties, carbon nanomaterials have now been extensively used synthesizing the nanocomposite materials that and used in many applications including microchannels, micro/nanoelectronics, textiles, paints, gas storage, composites, conductive plastics, displays, antifouling batteries with excellent durability during cycling-charge. The carbon quantum dots,

**3**

*Recent Developments in Nanocarbon-Polymer Composites for Environmental and Energy…*

as a newly emerging biocompatible material, have exhibited fluorescence properties and possess many other valuable excellent properties, such as high aqueous solubility, low cost, low toxicity, abundant surface functional groups and large active surface area for functionalization. Although, besides being used as bio compatible materials, such new class of (carbon quantum dots) nanomaterial are also applied as gas biosensors and heavy metal sensing applications [7, 17, 18]. In particular, the unique features of CQDs as up-converted photoluminescence (PL) behavior and photo-induced electron transferability of CQDs have proposed a new route for harvesting the sunlight from nonconventional reserve, to achieve efficient metal-

Fullerene as a new class of carbon family had introduced by Kroto, Curl and Smalley [22] in 1985 and denoted as buckminsterfullerene (C60). It is an intermediate allotrope of carbon between graphite and diamond as it constitutes from the bunch of atomic C*n* repeating unit (*n* > 20) which are collectively composed to form a spherical surface having a hollow core, or empty region of space inside the molecule. Carbon atoms are usually located on the surface of the sphere at the vertices of pentagons and hexagons and linked by forming sp2-hybridizing covalent bonds. Generally, C60 has two bond lengths, in which double bonds for 6:6 ring bonds are shorter than the 6:5 bonds. The important distinct characteristic ofC60 is that the pentagonal rings resulted in poor electron delocalization. As a result, C60 behaves like an electron deficient alkene, and reacts readily with electron rich species. C60

of formation 9.08 kcal/mol with boiling point of 800 K [23]. Fullerenes, due to its excellent properties like superconductivity, radical scavengers and excellent durability, are frequently applied in medicinal and electronics field, also in solar cell, fuel cell, cosmetic products (low order fullerene such as, C28, C26, etc.), biological/ medical area, catalysis and other relevant fields [24–26]. Furthermore, fullerene can

CNTs are one of the types of allotrope among carbon-based nanomaterials that have excellent mechanical and electrical properties. CNT are light-weighted, high strength material as compared to steel at nondimensional scale and discovered first by a Japanese scientist S. Ijimain 1991. Nowadays, due to its extraordinary graphic nature and high specific surface area have attracted attention and applied as a pillar material in many engineering applications like battery, electrochemical, pollutant remediation, and used as fillers for nanocarbon-polymer composites [28–30]. CNT exist broadly in two different shapes; cylindrical shaped is formed by rolling of the graphene sheets; and possessed cap fullerene structure appeared in half shape. Based on their geometrical configuration as proficiently qualified is experienced by high voltage electron microscopy techniques. CNT are further classified into two types (i) single-walled carbon nanotube (SWCNT), and (ii) multiwalled nanotube (MWCNT), Carbon nanotubes are prepared in rolled sheets of very few single layer carbon atoms (graphene) form cylindrical molecules. CNT with diameter 1–3 nm and length of few micrometers while for MWCNT, graphene sheets having 0.34 nm of inter-space distance, are stacked like concentric layers in cylindrical form of diameter 5–40 nm. Zhang et al. has been described in a reported literature, which is approximately 550 mm in length [31]. The properties of CNT are basically dependent upon the diameter, size and morphology. There are several methods are reported

, standard heat

is the odorless, and nonvolatile black solid having density 1.65 g/cm3

be easily modified to tailor properties for nanocomposites synthesis. [27].

*DOI: http://dx.doi.org/10.5772/intechopen.85626*

free photocatalysts [19–21].

**2.2 Carbon nanotubes**

**2.1 Fullerenes**

*Recent Developments in Nanocarbon-Polymer Composites for Environmental and Energy… DOI: http://dx.doi.org/10.5772/intechopen.85626*

as a newly emerging biocompatible material, have exhibited fluorescence properties and possess many other valuable excellent properties, such as high aqueous solubility, low cost, low toxicity, abundant surface functional groups and large active surface area for functionalization. Although, besides being used as bio compatible materials, such new class of (carbon quantum dots) nanomaterial are also applied as gas biosensors and heavy metal sensing applications [7, 17, 18]. In particular, the unique features of CQDs as up-converted photoluminescence (PL) behavior and photo-induced electron transferability of CQDs have proposed a new route for harvesting the sunlight from nonconventional reserve, to achieve efficient metalfree photocatalysts [19–21].

## **2.1 Fullerenes**

*Green Chemistry Applications*

mechanism that green chemistry offers a relatively lesser toxic synthesis approach, by reducing the harmful chemical substances in the designing the useful chemical products [6]. Nowadays, due to the unique properties of carbon-based nanomaterials like good electrical conductivity, ease in surface functionalization, high mechanical strength and good thermal stability of carbon-based fullerenes carbon nanotubes (CNTs), carbon quantum dots and graphene, attracted high interest toward research and used widely in many application purposes. Therefore, in the reported literatures, as wonder materials, carbon-nanomaterials have been used directly or modified for aforesaid applications [7]. Although, following complex techniques and expensive hydrocarbons or other specific hazardous source like laser are not easy to handle in different synthesis routes like chemical vapor deposition (CVD), plasma CVD, laser ablation used for the synthesizing the different carbonbased nanomaterials. There are some reported literatures in which an inexpensive and environmentally friendly approach is exploited for recovering the carbon based nanomaterials and experimentally particularly shown their applicability in remediation and sensing applications [8–14]. The synthesis of nanocomposites plays leading role in the current advanced applications purposes such as, energy storage,

electronics parts, environmental remediation, biomedicine, etc. [15].

**2. Classifications of carbon and carbon-based nanomaterials**

materials is introduced. In recent past years, the different types of carbon nanomaterials have been experimentally tested and successfully developed as advance materials in many engineering applications. In general, carbon nanomaterials exist in between 1 and 100 nm size range; therefore, the unique properties of carbon nanomaterials like good electrical, ionic conductivity, high mechanical and thermal stability at the nanoscale compared with other materials are exceptional and competent for many engineering applications [16]. Carbon nanomaterials are classified further based on their shape and geometrical structures, till dates different forms of carbon nanomaterials that are existing; horn-shaped as nanohorns, tube-shaped as carbon nanotube (CNT), ellipsoidal spherical shape carbon nanospheres (fullerenes), and zero-dimension dots exhibited quantum character as carbon quantum dots (CQDs). Because of excellent properties, carbon nanomaterials have now been extensively used synthesizing the nanocomposite materials that and used in many applications including microchannels, micro/nanoelectronics, textiles, paints, gas storage, composites, conductive plastics, displays, antifouling batteries with excellent durability during cycling-charge. The carbon quantum dots,

efficacy for the previously mentioned applications.

Present book chapter deals with production and potential applications of nanocarbon and nanocarbon-polymer composite materials, with special attention on the energy and environmental related sector and their significant role in enhancing the

Carbon have tendency to polymerize into the large molecular weight compounds with long chains due to its unique electronic construction and the smaller size in comparison of group IV that makes it capable of linking with other elements. As it contains four electrons in the valence layers, carbon can easily form covalent bonds with both metals and non-metals. Due to this property, carbon-based compounds can exist in diverse molecular forms, and same type of atoms can be arranged in the different shapes, with different properties known as allotropes. Graphite and diamond are two known natural occurring allotropes of carbon found in the ecology and formed other multiple allotropes of carbon from natural carbon sources for the different purposes. Furthermore, with the knowledge of top down and bottom up approaches of nanotechnology, a new family of carbon nanomaterials as wonder

**2**

Fullerene as a new class of carbon family had introduced by Kroto, Curl and Smalley [22] in 1985 and denoted as buckminsterfullerene (C60). It is an intermediate allotrope of carbon between graphite and diamond as it constitutes from the bunch of atomic C*n* repeating unit (*n* > 20) which are collectively composed to form a spherical surface having a hollow core, or empty region of space inside the molecule. Carbon atoms are usually located on the surface of the sphere at the vertices of pentagons and hexagons and linked by forming sp2-hybridizing covalent bonds. Generally, C60 has two bond lengths, in which double bonds for 6:6 ring bonds are shorter than the 6:5 bonds. The important distinct characteristic ofC60 is that the pentagonal rings resulted in poor electron delocalization. As a result, C60 behaves like an electron deficient alkene, and reacts readily with electron rich species. C60 is the odorless, and nonvolatile black solid having density 1.65 g/cm3 , standard heat of formation 9.08 kcal/mol with boiling point of 800 K [23]. Fullerenes, due to its excellent properties like superconductivity, radical scavengers and excellent durability, are frequently applied in medicinal and electronics field, also in solar cell, fuel cell, cosmetic products (low order fullerene such as, C28, C26, etc.), biological/ medical area, catalysis and other relevant fields [24–26]. Furthermore, fullerene can be easily modified to tailor properties for nanocomposites synthesis. [27].

#### **2.2 Carbon nanotubes**

CNTs are one of the types of allotrope among carbon-based nanomaterials that have excellent mechanical and electrical properties. CNT are light-weighted, high strength material as compared to steel at nondimensional scale and discovered first by a Japanese scientist S. Ijimain 1991. Nowadays, due to its extraordinary graphic nature and high specific surface area have attracted attention and applied as a pillar material in many engineering applications like battery, electrochemical, pollutant remediation, and used as fillers for nanocarbon-polymer composites [28–30]. CNT exist broadly in two different shapes; cylindrical shaped is formed by rolling of the graphene sheets; and possessed cap fullerene structure appeared in half shape. Based on their geometrical configuration as proficiently qualified is experienced by high voltage electron microscopy techniques. CNT are further classified into two types (i) single-walled carbon nanotube (SWCNT), and (ii) multiwalled nanotube (MWCNT), Carbon nanotubes are prepared in rolled sheets of very few single layer carbon atoms (graphene) form cylindrical molecules. CNT with diameter 1–3 nm and length of few micrometers while for MWCNT, graphene sheets having 0.34 nm of inter-space distance, are stacked like concentric layers in cylindrical form of diameter 5–40 nm. Zhang et al. has been described in a reported literature, which is approximately 550 mm in length [31]. The properties of CNT are basically dependent upon the diameter, size and morphology. There are several methods are reported

for CNT preparation like arc discharge, laser ablation, chemical CVD, and plasma CVD. Among the listed methods, arc discharge was the first technique used for the preparation of CNT while laser-ablation method was used to prepare the SWCNT. In the chemical CVD method, small amount of metallic catalysts (Ni and Co) are used to catalyze the hydro-carbon as source at relatively lower temperature for the growth of graphitic surface. The high enhanced electrical property of SWCNTs is due to the presence of the chirality or hexagon orientation with respect to the tube axis, however on bulk scale its synthesis process is very complex and not easy to control the layers. In contrast to the SWCNT, due to the presence of multiple layers, MWCNT possess high mechanical and thermal satiability. Further, based on SWCNTs morphology, it is classified into three subgroups: (i) armchair morphology exhibiting high electrical conductivity than the copper, (ii) zigzag morphology has good semiconductor property and (iii) chiral morphology has semi-conductive property.

#### **2.3 Graphene**

Graphene is two dimensional, single-atom layer of carbon atoms which are sp2 hybridized and fixed in a rigid hexagonal lattice like a flat plane. Graphene is also a primitive building element of graphite, fullerene and CNT, Graphene was discovered in 2004 by Canadian physicist Wallace. It is an allotropic form of carbon with bond length of 0.142 nm between neighboring atoms of carbon and layer by layer of graphene is stacked with an interplanar spacing of 0.335 nm. The layers of graphene in graphite are bounded by Van der Waal forces [32, 33]. The unique physical properties of graphene, such as, thermal stability, mechanical rigidity and electrical conductivity are higher for few layers of graphene than of their three-dimensional materials. Also, graphene conducts high heat because of high thermal conductivity of graphene in comparison with available excellent heat conductors such as, silver and copper, and much better than graphite and diamond [7, 33].

#### **2.4 Carbon quantum dots**

A new class of with unique fluorescent property of carbon nanoparticles discovered accidentally Xu et al. in [34] during purification of SWCNTs. Later in 2006, Sun et al. had given a name of such fluorescent materials as carbon quantum dots (CQDs) particle of size found less than 10 nm. Till date, due to its fascinating property (harvesting optical light and imparting multicolor tuned emission) of CQDs offers a surprising potential material in fields of bio-imaging, photo-degradation and catalysis applications [35]. In last decade, various chemical precursors like citric acid, ammonium citrate, ethylene glycol, benzene, phenylenediamine, phytic acid, and thiourea, have been used for synthesizing CQDs. In order to minimize energy consideration, various synthetic methods, including hydrothermal, solvothermal, electrochemical, microwave assisted pyrolysis, ultrasonication, and chemical oxidation, etc., have been tested to produce the fluorescent CQDs. A number of review and research papers have been focused on the synthesis of such CQDs [36–39]. However, to date there has not been a very few reviews which explicitly focused on green synthesis routes is discussed in details for sensing and bio-imaging of applications [40].

**Figure 1** describes the different types classification of synthesis routes used in developing the different types of nanocarbons.

#### **2.5 Naturally occurring synthesis nanocarbon**

Nanocarbons occur naturally, but not available at abundant scale; therefore, this approach is not very conventional to control the number of graphitic layers,

**5**

*Recent Developments in Nanocarbon-Polymer Composites for Environmental and Energy…*

therefore their physical and chemical properties of nanocarbon may vary for engineering applications. There are different types of nanocarbon available from natural synthesis are reported in literature [41]. Velasco-Santos et al. described the existence of carbon nanotubes in the coal/petroleum mixture [42]. SWCNT can be synthesized by CVD, Su and Chen, 2007 and Mracek et al. 2011used metal oxide mixed volcanic lava as a substrate and catalyst [43, 44]. It was noted that process may provide indication for a probable creation of nanomaterials in natural conditions when the temperature rises extremely high, e.g., during volcano eruptions. Like CNT and SWCNT, fullerenes are also found in different ecological materials, for example in the natural mineral shungite from Karelia fullerene is found in low concentrations (2% w/w) [45] and also in meteorite samples of cosmic origin [46]. Chitin is one of the naturally occurring nanomaterials obtained from carbohydrate polymer. Synthesis of chitin nonmaterial considers the following factors such as, thermal dimensional stability, dispersibility, mechanical reinforcements, antibacterial activity etc. depending on the specific goals [47]. Natural nanomaterials can be obtained from polymer waste and its feasibility depends upon processing, recycling,

Chemical functionalization process formed a huge distinct variety of carbonbased nanomaterials having different functionality, which are applied successfully in different sectors. As the surface functionalization means, carbon-based nanomaterials are added with other groups that ultimately changed its chemical and physical properties [49, 50]. There are many methods of functionalization available for carbon based nanomaterial, such as oxidation, ionic/non-ionic aliphatic aqueous (Hydrophobic), Ionic/Non-ionic aromatic (π-π stacking), Van der Waals' force (Attraction), Wrapping, doping, and direct deposition. The modification of surfaces is depending on the feasibility and degree of functionalization for the specific application. Therefore, in light of specific application, materials have been synthesized by following different mechanisms like non-covalent bonds, covalent bonds, electrostatic force, hydrogen bonds, Van-der Waals force etc. [51]. Some example of surface modification are as follows; Jiang et al. covered the CNT surface with active sulfate groups by using sodium dodecyl sulfate (NaC12H25SO4) a common surfactant (anionic) for dispersing the sulfate groups [52]. In oxidation process CNT are exposed to mixture of acids via ultrasonic treatment method, during this

*DOI: http://dx.doi.org/10.5772/intechopen.85626*

*Types of synthetic routes of different nanocarbons.*

transportation cost, etc. [48].

**Figure 1.**

**2.6 Chemically functionalized nanocarbons**

*Recent Developments in Nanocarbon-Polymer Composites for Environmental and Energy… DOI: http://dx.doi.org/10.5772/intechopen.85626*

#### **Figure 1.**

*Green Chemistry Applications*

**2.3 Graphene**

**2.4 Carbon quantum dots**

for CNT preparation like arc discharge, laser ablation, chemical CVD, and plasma CVD. Among the listed methods, arc discharge was the first technique used for the preparation of CNT while laser-ablation method was used to prepare the SWCNT. In the chemical CVD method, small amount of metallic catalysts (Ni and Co) are used to catalyze the hydro-carbon as source at relatively lower temperature for the growth of graphitic surface. The high enhanced electrical property of SWCNTs is due to the presence of the chirality or hexagon orientation with respect to the tube axis, however on bulk scale its synthesis process is very complex and not easy to control the layers. In contrast to the SWCNT, due to the presence of multiple layers, MWCNT possess high mechanical and thermal satiability. Further, based on SWCNTs morphology, it is classified into three subgroups: (i) armchair morphology exhibiting high electrical conductivity than the copper, (ii) zigzag morphology has good semiconductor property and (iii) chiral morphology has semi-conductive property.

Graphene is two dimensional, single-atom layer of carbon atoms which are sp2 hybridized and fixed in a rigid hexagonal lattice like a flat plane. Graphene is also a primitive building element of graphite, fullerene and CNT, Graphene was discovered in 2004 by Canadian physicist Wallace. It is an allotropic form of carbon with bond length of 0.142 nm between neighboring atoms of carbon and layer by layer of graphene is stacked with an interplanar spacing of 0.335 nm. The layers of graphene in graphite are bounded by Van der Waal forces [32, 33]. The unique physical properties of graphene, such as, thermal stability, mechanical rigidity and electrical conductivity are higher for few layers of graphene than of their three-dimensional materials. Also, graphene conducts high heat because of high thermal conductivity of graphene in comparison with available excellent heat conductors such as, silver

A new class of with unique fluorescent property of carbon nanoparticles discovered accidentally Xu et al. in [34] during purification of SWCNTs. Later in 2006, Sun et al. had given a name of such fluorescent materials as carbon quantum dots (CQDs) particle of size found less than 10 nm. Till date, due to its fascinating property (harvesting optical light and imparting multicolor tuned emission) of CQDs offers a surprising potential material in fields of bio-imaging, photo-degradation and catalysis applications [35]. In last decade, various chemical precursors like citric acid, ammonium citrate, ethylene glycol, benzene, phenylenediamine, phytic acid, and thiourea, have been used for synthesizing CQDs. In order to minimize energy consideration, various synthetic methods, including hydrothermal, solvothermal, electrochemical, microwave assisted pyrolysis, ultrasonication, and chemical oxidation, etc., have been tested to produce the fluorescent CQDs. A number of review and research papers have been focused on the synthesis of such CQDs [36–39]. However, to date there has not been a very few reviews which explicitly focused on green synthesis routes is discussed in details for sensing and bio-imaging of applications [40]. **Figure 1** describes the different types classification of synthesis routes used in

Nanocarbons occur naturally, but not available at abundant scale; therefore, this approach is not very conventional to control the number of graphitic layers,

and copper, and much better than graphite and diamond [7, 33].

developing the different types of nanocarbons.

**2.5 Naturally occurring synthesis nanocarbon**

**4**

*Types of synthetic routes of different nanocarbons.*

therefore their physical and chemical properties of nanocarbon may vary for engineering applications. There are different types of nanocarbon available from natural synthesis are reported in literature [41]. Velasco-Santos et al. described the existence of carbon nanotubes in the coal/petroleum mixture [42]. SWCNT can be synthesized by CVD, Su and Chen, 2007 and Mracek et al. 2011used metal oxide mixed volcanic lava as a substrate and catalyst [43, 44]. It was noted that process may provide indication for a probable creation of nanomaterials in natural conditions when the temperature rises extremely high, e.g., during volcano eruptions. Like CNT and SWCNT, fullerenes are also found in different ecological materials, for example in the natural mineral shungite from Karelia fullerene is found in low concentrations (2% w/w) [45] and also in meteorite samples of cosmic origin [46]. Chitin is one of the naturally occurring nanomaterials obtained from carbohydrate polymer. Synthesis of chitin nonmaterial considers the following factors such as, thermal dimensional stability, dispersibility, mechanical reinforcements, antibacterial activity etc. depending on the specific goals [47]. Natural nanomaterials can be obtained from polymer waste and its feasibility depends upon processing, recycling, transportation cost, etc. [48].

## **2.6 Chemically functionalized nanocarbons**

Chemical functionalization process formed a huge distinct variety of carbonbased nanomaterials having different functionality, which are applied successfully in different sectors. As the surface functionalization means, carbon-based nanomaterials are added with other groups that ultimately changed its chemical and physical properties [49, 50]. There are many methods of functionalization available for carbon based nanomaterial, such as oxidation, ionic/non-ionic aliphatic aqueous (Hydrophobic), Ionic/Non-ionic aromatic (π-π stacking), Van der Waals' force (Attraction), Wrapping, doping, and direct deposition. The modification of surfaces is depending on the feasibility and degree of functionalization for the specific application. Therefore, in light of specific application, materials have been synthesized by following different mechanisms like non-covalent bonds, covalent bonds, electrostatic force, hydrogen bonds, Van-der Waals force etc. [51]. Some example of surface modification are as follows; Jiang et al. covered the CNT surface with active sulfate groups by using sodium dodecyl sulfate (NaC12H25SO4) a common surfactant (anionic) for dispersing the sulfate groups [52]. In oxidation process CNT are exposed to mixture of acids via ultrasonic treatment method, during this

process, carboxylic groups (–COOH) is attached with CNT surfaces. Oxidation of CNT is very important and creates oxygen carrying groups (–COOH and –OH), which makes CNT feasible for further functionalization without affecting their electrical and mechanical properties [7].
