Advanced Carbon Materials: A Comprehensive Overview

#### **Chapter 1**

## Introductory Chapter: Introduction to Advanced Carbon Materials and Innovative Engineering Applications

*Sadia Sharif, Sana Arbab, Amna Saeed, Khurram Shahzad, Muhammad Aamir Iqbal, Abdullah Khan Durrani, Asghari Maqsood and Mujtaba Ikram*

#### **1. Introduction**

Carbon belongs to the group IV of periodic table with atomic number 6. Graphite, diamond and fullerene are the allotropic forms of carbon. Carbon-based materials are versatile in term of applications due to its nature to chemically combine with other carbon-based materials and to make a strong covalent bond with a range of different elements. Therefore, they have outstanding properties like high strength, high density, and high hardness. The amazing characteristics of carbon materials make them most suitable candidate in various applications of advance technology. Graphene, carbon fibers, carbon foams, structural graphite (special graphite), carbon nanotubes (CNT), diamond-like carbon (dlc) and nano-crystalline diamond (ncd) are all included in advance carbon materials category. Advance carbon material are backbone of next generation scientific revolution especially in field of nanotechnology and materials sciences, respectively. Advanced carbon materials which are graphene, fullerenes, CNTs are considered most researched nanostructures in last couple of decades. Due to outstanding physical properties of advanced carbon monoliths, it has been used in photovolatic, environment, energy, thermal, and electronic applications. 21st century is being considered as "Scientific era of graphene", which is most amazing form of carbon due to highest electrical conductivity, thermal conductivity, strength and permeabile properties. Graphene is a material which conducts electricity and heat to maximum, which makes it an ideal candidate for energy and thermal applications, respectively. The following chapter will have a detailed insight in various forms of advanced carbon materials especially graphene, structural graphite, carbon nanotubes, diamond-like carbon (DLC), carbon foam and fullerene, respectively. The chapter grants detailed insight into physical properties and applications of advanced carbons materials.

#### **2. Types of advanced carbon materials and related application**

#### **2.1 Graphene**

Graphene is first ever 2-D allotropic form of carbon with hybridized Sp2 bonding which gave rise to new advancements in research and technology. The mysterious

**Figure 1.** *Descriptive illustration of various structures of graphene.*

electronics, structural, electrochemical, and physicochemical features of single layer of this material are significantly the big concern for the material scientists [1–4]. Mono atomic carbon layer extending across the two provided large surface areas due to an incredibly porous material [5], representing its potent absorbing ability. Hereby, scientists may conclude that it is a great adsorption applicant.

Thanks to the intersection among conduction and valence band at six positions in momentum at the Dirac points, graphene is often considered a zero-gap semiconductor [6]. Zero band gap depicts "zigzag" with the presence of an "armchair". Descriptive illustration of various structure of graphene is represented in **Figure 1**. Moreover, high charge room temperature durability, as demonstrated by previous research, is 15000 cm<sup>2</sup> .V−1.s−1 [7]. In some earlier studies, the identical charge flexibility for hole and electron was also stated [8–11]. The splitting stability of charge carriers at a room temperature of audible graphene phonons is noted to be 4.5 × 103 times more than copper [12]. At room temperature, graphene plates give lowest resistivity 10−6 Ω cm, which is lower compared to silver [13]. Graphene in twisted bilayer form exhibited superconductivity [8, 14]. Owing to its adsorption power which is nearly 2.3% of the red light, and approximately 2.6% of the green light, the mono-atomic dense bilayer surface can be observed with the naked eye [14]. Graphene has an exceptional clarity for monolayer atomic structure in vacuum [15]. Thermal behavior, one of the key characteristics of graphene, an efficient and desirable tested route for many researchers because of its high ability in thermal applications. In previous experiments, a comparative study of graphite and graphene found that the thermal conductivity varies in both materials at room temperature which are 2000 W.m−1.K−1 and 5300 W.m−1.K−1, respectively [16]. However, recent progress has demonstrated that the former thermal conductivity value is sustainable, in fact it ranges from 1500 to 2500 W·m−1·K−1 for individual layer of graphene [17–25].

Graphene has two dimensions. The LA and TA showed linear dispersion relation whereas the quadratic scattering relation was observed because of off-plane mode. That is why the linear dispersion mode has high thermal conductivity relative to the off-plane mode [26]. The negative GPs found by the phonon graphene bands and at low temperatures are significant, while the clear link between the negative GPs and thermal expansion coefficient [27]. The graphene structure is layered and the spacing is around 0.335 nm between each sheet. Toughness of graphene is 130 GPa and

*Introductory Chapter: Introduction to Advanced Carbon Materials and Innovative Engineering... DOI: http://dx.doi.org/10.5772/intechopen.95969*

it has 1TPa Young's Modulus, which is why it is significantly a stronger material than others [28]. Scientists have found that Graphene monolayer have a large-angle-bent, which gives a slight strain, so 2D carbon monoliths displayed important mechanical and physical features. Moreover, the charge mobility in the monolayer of graphene does not alter after high disruption [29].

#### *2.1.1 Applied applications of graphene based materials*

Graphene is versatile material owing to excellent physical properties. It has been used in many applications in industry and environment. Following are the applications of components from graphene.


#### **2.2 Structural graphite**

The word "Graphite" is taken from a Greek-word "graphein" having meanings of "to write". This is a grayish-black naturally-occurring carbon-material with a radiant black-shine. It is a unique material which shows properties of both crystalline & non-crystalline and of a metal & non-metal. On this basis, graphite can be classified as natural and synthetic-graphite.

#### **2.3 Natural-graphite**

Naturally-occurring graphite is further grouped into three classes:


#### *2.3.1 Crystalline or structural-graphite*

Graphite has a layer-structure with hexagonal-arrangement of C-atoms containing covalent-bonding "honeycomb-structure". The layers are stacked together by secondary-bonding type that is, Van-der-Waals interactions which measure the weak shear-strength of graphite. Therefore, by applying a small shear-stress, deformation in structure happens and thus graphite comes out to be anisotropic where properties depend on the direction of applied-force. In structural-graphite, every C-atom is covalently associated to three neighboring C-atoms and that is how each atom leaves a spare free-electron. These free-electrons form a delocalizedcloud of electrons which is weakly bonded to layers which is an ultimate-reason of graphite's good electrical-conductivity along each layer [52]. Structure of graphite is respresented in **Figure 2**.

#### *2.3.2 Artificial or synthetic-graphite*

Artificial-graphite is obtained by graphitization of nongraphitic carbon and via chemical-vapor-deposition CVD from hydro-carbons using higher temperatures. This graphite is not highly crystalline as natural-graphite or structural-graphite. Example includes synthetic-graphite obtained via heating calcined-petroleum at about 2800°C.

#### *2.3.3 Applied applications and physical properties of graphite*

On account of structural, chemical and mechanical properties of graphite, some important applications are listed in the table below:


#### **2.4 Carbon foam (C-foam)**

The C-materials are best known for their wide-range porous-structure with variety of size and number of pores [55, 56]. Among fibrous, tubular, granular and other platelet & spherical morphologies of C-materials, C-foam has a particular-pore organization, where there is an interconnection of various macropores (cells) to form an open-cell-structure. Actually, this unique cell-structure defines the novel characteristics and features of these substances such as low density, high thermalstability, water resistive surfaces, efficient thermal and electrical-conductivities, etc.

*Introductory Chapter: Introduction to Advanced Carbon Materials and Innovative Engineering... DOI: http://dx.doi.org/10.5772/intechopen.95969*

Thermal and electrical conductivities can be altered for bulky-C-products by making controlled-changes in the internal. Cell-structure to define C-foam can be understood thoroughly from the SEM-image in **Figure 3**. Two distinct pores can be observed in the image: a macropore called "cell" which is surrounded by "C-wall" and other is a hole in C-wall called "window". Window connects the neighboring cells together to form a Cell-structure. With these terminologies, the concept of C-foam is described as: Components with enlarged pores where cells (macropores or sometimes mesopores) are interconnected through windows and thus provide space to introduce other types of substances inside the pores to increase substrate compatibility [58].

*2.4.1 Applied application and physical properties of C-foam*


#### **2.5 Carbon nanotubes (CNTs)**

As the name suggests, these are tubes of carbon with diameters of nanometerrange which are also known as "bucky-tubes". The tubular C-structure was first studied in 1991 by Iijima [66, 67]. These were named as "multi-walled CNTs

**Figure 4.** *(a) SW-NT [4] & (b) MW-NTs [71].*

(MW-CNT)". Single-partition (SW) CNT was synthesized by Bethune [68]. Both the types can synthesize using three methods: arc-ablation, thermal decomposition and catalytic-growth. To understand the structure of SW-CNT, structure of crystalline-graphite should be known. As graphite contains stacked-layers of hexagonally-arranged C-atoms with sp2 -configuration. The stacking of these layers is due to inter-molecular forces and separately single layer is known as "graphene sheet". Each nanotube comprises of millions of C-atoms and in SW-NT only ten atoms are arranged at circumference and thickness of tube is ~1 atom [69, 70]. The structures of single wall and multi wall nanotubes are shown in **Figure 4**.

#### *2.5.1 Applied applications and physical properties of CNT's*

CNTs show a great combination of superlative-mechanical, electrical and thermal properties which is mainly due to sp2 C-C bonding ability. These properties have opened their ways to the various areas of industrial-applications, some of them are listed below.


#### **2.6 Fullerene**

The fullerene discovery in 1985 has revotulized the scientific field. It has been used widely in physical, biological and chemical applications, respectively. Amazing physical properties are attribute of C60, which is actually a member of fullerene family.

#### **2.7 Diamond-like carbon (DLC)**

Diamond-like carbon (DLC) is undefined carbon [75, 76]. In DLC, considering the hybridization of sp3, no periodicity exists because of the heterogeneity of the

*Introductory Chapter: Introduction to Advanced Carbon Materials and Innovative Engineering... DOI: http://dx.doi.org/10.5772/intechopen.95969*

bond angle C-C-C. The DLC has low density than that of diamond. Preferably DLC is composed of only sp3 carbon atoms. The processed content, though, sometimes contains sp3 and s2 carbon atoms. The existence of sp2 carbon atoms does not make the substance electrically isolated. In terms of hardness and thermal conduction, DLC is not as strong as diamond, but is much cheaper. The DLC is widely used for painting purposes for better wear resistance and thermal conductivity, owing to its low coefficient of friction. The DLC is normally produced by plasma enhanced chemical vapor deposition (PECVD. The accumulation conditions vary from DLC to diamond. The DLC is hydrogenated frequently during its development to inactive the collar bonds. Such passivation is beneficial to minimize the electric capacitance in the DLC [77].

#### **3. Conclusion**

Advanced carbon materials are backbone for scientific revolution of 21st century especially in nanotechnology. Carbon nanotubes (CNTs) and graphene are most researchered nanomaterials for the last decade due to outstanding physical properties. Graphene, being the first ever 2-D material, bring huge opportunities and potential for novel materials research due to good electrical conductivity, thermal conductivity, tensile strength and good dielectric properties, respectively. Due to unique characteristics of graphene monoliths, it has been employed in various fields such as electrical, thermal. Mechanical, and optical applications. In conclusion, advanced carbon materials will be the driving force for next generation scientific revolution.

#### **Author details**

Sadia Sharif1 , Sana Arbab2 , Amna Saeed<sup>2</sup> , Khurram Shahzad<sup>2</sup> , Muhammad Aamir Iqbal3 , Abdullah Khan Durrani2 , Asghari Maqsood4 and Mujtaba Ikram2 \*

1 Department of Physics, Government College University, Lahore, Punjab, Pakistan

2 Institute of Chemical Engineering and Technology (ICET), University of the Punjab (PU), Lahore, Punjab, Pakistan

3 School of Materials Science and Engineering, Zhejiang University, China

4 Nanoscale Laboratory, Department of Physics, Air University, Islamabad, Pakistan

\*Address all correspondence to: mujtaba.icet@pu.edu.pk

© 2021 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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#### **Chapter 2**

## Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer, Sensing and Energy Engineering

*Muhammad Ikram, Ali Raza, Khurram Shahzad, Ali Haider, Junaid Haider, Abdullah Khan Durrani, Asim Hassan Rizvi, Asghari Maqsood and Mujtaba Ikram*

#### **Abstract**

Advance carbon material that includes graphene, fullerenes, hierarchical carbon, and CNTs are referred to as strength of revolution and advancement in the era of material science and technology. In general, 20th century corresponds to plastic meanwhile 21st century will be named as "Century of Graphene" owing to its exceptional physical properties. Graphene is now well-known and prominent 2D carbon allotrope that is considered as multipurpose material in comparison with any material discovered on earth. One of the interesting properties of graphene is strongest and lightest material that enables it to conduct electricity and heat as compared to any other material. Such features permit it to utilize in numerous applications including biosensors, electronic industry, environmental remediation, drug delivery, energy storage, and production as well. Owing to these capabilities, it can be stated that graphene can be utilized to improve effectiveness and performance of existing substances and materials. In the future, conjugation of graphene with other 2D material will be devolved to produce further remarkable compounds that make it appropriate for an extensive variety of applications. This chapter grants the utilization and applications of advanced carbons materials in chemical, polymer, sensing and energy enegineering.

**Keywords:** polymer composites, nano coatings, lubricants, nanofluids, biosensors, fuel cells, supercapacitors

#### **1. Introduction**

Carbon has been distinguished into variety of forms as amorphous carbon, diamond, and graphite. Among these, the well-recognized allotropes of carbon since ancient times are diamond and graphite. The third kind of carbon named fullerene was discovered by Kroto et al. in 1985 whereas; carbon nanotubes (CNTs) were discovered by Iijima in 1991 that leads to gain a significant role in the field of science and technology. Accordingly, only three kinds of carbon allotropes were identified and well-known in the carbon family are first, diamond and graphite

(3D) secondly, CNTs (1D) and thirdly, fullerenes (0D). Later, in 1991 it was realized that CNTs were fabricated by rolling of 2D graphene single sheet that was extracted from 3D graphitic material [1–3]. Furthermore, isolation of graphene was somewhat struggling and indefinable concerning any effort corresponds to experimental research until 2004. Graphene is an elementary structural element of CNTs, fullerenes, and graphite that are named as allotropes of carbon family. Fullerene is entitled as buckyball as it is composed of carbon sheets in the arrangement of spherical profile. In comparison with fullerene, CNTs acquire tubular form. For more than two decades, CNTs and fullerene-based martial expose extensive applications in the varied portion of the research that involve biosensors, super-capacitors, electrochemical sensors, electronics, fuel cells, batteries, and medicinal applications. Presently, graphene is entitled as "Rising Star Candidate" after its effective production from scotch tape process by utilizing voluntarily accessible graphite by Andre Geim and his coworkers in 2004. Single-layer sheets of graphene consist of carbon atom that is sp2 bonded and acquires honeycomblike lattice which is densely packed. As an active material, remarkable properties of graphene that include tunable bandgap, high specific surface area, superior thermal, electrical stability and conductivity, and more importantly Hall effect (at room temperature) provides suitable platform for its utilization in the production of several composites materials [4]. Struggles were devoted to reviewing the structure and preparation of graphene its properties, possible applications, and finally composite material [5–8]. At present, owing to possess remarkable properties, graphene is shortlisted as the most widespread material that can be employed for several devices and applications. This chapter grants the utilization and applications of graphene in various approaches, the synthesis routes, and numerous exceptional properties.

#### **2. Application**

Previously, graphene has illustrated promising impression to various information communication technology areas that sorts from a high-performance application (top-end) in ultrafast information processing (i.e. THz) to consumer applications by means of flexible electronic structures. An authentic property of graphene is verified by the increment in the score of chip makers now energetic in research based on graphene. Prominently, graphene is reflected as the emerging candidate that can be utilized for post-Si-electronics. Most auspicious applications of graphene contain light processing, sensors, electronics, plasmonics, energy storage, meta-materials, generators, etc. Besides, graphene is utilized to enhance various industrial and medical processes. The overview for the applications of graphene is displayed in **Figure 1**.

#### **2.1 Polymer composites**

Biphasic materials are considered as polymeric composites, which are attained by dispersing one phase into another controllably. Modified graphene may be dispersed into polymer-matrix to become reinforcing-filler to increase optimally physiochemical properties [10]. Firstly, Stankovich et al. presented phenyl isocyanated graphene acting as nanofiller during the synthesis of polystyrene (PS)/graphene matrix [11]. It was observed that only 2.4 vol% increments belonging to surface-modified graphitic compound filled desired composites, caused by enlarged surface area graphitic composite. The electrical conductivity attained percolation threshold by incorporating about ~0.1 vol% graphene as illustrated **Figure 2**. Reports offered by Eda et al.

*Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

**Figure 1.** *Overview of applications of advanced carbon material (graphene) [9].*

#### **Figure 2.** *Electrical conductivity of phenyl isocyanate modifi ed. graphene filled polystyrene composites [11].*

exhibited functionalized graphitic filled PS-composites showing the same electrical properties as that of monolayer rGO nanosheets [12]. Whereas PS-composites are being explored p-type semiconducting nature at high temperatures.

Kuila et al. reported that dodecyl-amine (DA) along with octadecy-amine (ODA) functionalized graphitic filler during synthesis of linear-low-density polyethylene (LDPE), while ethylene-vinyl-acetate (EVA) composites were obtained respectively [13–16]. Modified-graphene was well dispersed in LLDPE as well as EVA matrix during hydrophobic-interaction with alkyl-chains of polymer matrix along with modifier. As far as tensile strength is concerned, it acts with storagemodulus collectively to composites as they are increased with surface-modified graphene optimally to a certain limit, thereby decreasing with additional fillers. Epoxy graphitic composites have been detailed in investigation processes [17–19]. It has been keenly observed that little increment of surface-modified graphitic material increasingly enhances mechanical as well as thermal stability as compared with neat epoxy. This corresponds to reasonable surface area along with superior mechanicalstrength attributing to graphene composite. Some other usable polymers for graphitic-composite preparation are known as polyvinyl-alcohol, crystal-polymers, polypropylene, polypyrrole, polymethyl methacrylate chitosan, cellulose, polycarbonate, polyethylene terephthalate, and polyvinyl chloride [20–25]. Graphiticpolymers offer potential applications towards automobiles, air-craft industry, turbine blades, bony structures, and tissue culture implantations [26–30].

#### **2.2 Nano coatings: antimicrobials and microelectronics**

Carbon nanotubes show a promising multifunctional nature material in coating fabrication. Metal decorated CNTs are considered as hybrid-systems that may be prepared by using those CNTs having carboxyl-groups, binding transition metal ions such as Ag+ and Cu2+. These aforesaid ions contribute a large part to their superior antimicrobial activity to destroy bacterial as well as fungus microbes along with less cross-resistance towards antibiotics (see **Figure 3a** and **b**) [31]. MWCNTs with paint materials successfully reduce biofouling-ship-hulls owing to discourage embodied algae with barnacles [32]. Consequently, they are referred to as alternatives for environmentally polluted biocide type paints. Anticorrosion-coatings include CNTs for metals for enhancement of coating-stiffness and strengthen them to make an electric pathway to create cathodic protection.

Widespread progress has been made for fabrication of CNTs that are based on flexible and transparent conductive thin films [33–35] proving alternative material of indium tin oxide. The main issue concerning ITO is its expensive nature owing to shortage of indium. However immense need for displays, touchscreens and photovoltaic provide stimulus. Moreover, CNTs flexibility raise the transparency of conductors showing a major advantage over ITO coatings towards flexible displays. Additionally, transparent CNTs conductors are deposited from solutions such as slot-die coating as well as ultrasonic spraying along with cost-effective nonlithographic approaches likewise micro-plotting. The latest effort has been made for fabrication of CNTs films showing 90% transparency with 100-ohm resistivity per square as is clear from **Figure 4**. Surface resistivity so much appeared is considerably suitable for promising applications. However, substantially it is better than equally transparent and optimal doping with ITO coatings [36]. Widespread applications have exhibiting requirements relevant to CNTs thin-film-heaters and are substantially used for defrosting automobile-windows as well as sidewalks. Aforesaid all types of coatings are widely used on an industrial level.

Recently, CNTs films are transparent; however, stretchable flexible may often tailor in the form of shapes and sizes. They are freestanding and are placed on rigid or flexible insulated surfaces. A piece of carbon nanotube CNTs thin films may explore magnet-free-loudspeaker. It may simply show through applying an audiofrequency-current passing through it depicted in **Figure 5**. CNTs film loudspeaker produces sound waves with high-frequency range, a wide range of sound pressurelevel along with low harmonic-distortion [37]. These CNTs thin films behave like transistors, proving more attractive towards driving organic light-emitting-diode

#### **Figure 3.**

*Comparison in functional mechanism between small molecular antibiotics and macromolecular antimicrobials (a) mechanisms of antibiotic resistance in bacteria, (b) mechanism of membrane-active antimicrobial peptides.*

*Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

#### **Figure 4.**

*Carbon nanotubes flexible transparent conducting film ((image courtesy Plasticstar material news).*

#### **Figure 5.**

*Carbon nanotube thin film loudspeakers (a) the CNT thin film was pulled out from a super aligned CNT array grown on a 4 in. Silicon wafer and put on two electrodes of a frame to make a loudspeaker. (b) SEM image of the CNT thin film showing that the CNTs are aligned in the drawing direction. (c) A4 paper size CNT thin film loudspeaker. (d) the cylindrical cage shape CNT thin film loudspeaker can emit sounds to all directions, diameter 9 cm, height 8.5 cm [39].*

screen display. Because of this reason, they have explored higher-mobility as compared with amorphous silicon, depositable by low-temperature, and vacuum-free approaches. Today flexible CNTs -TFTs having mobility 35 cm2 V−1 s−1, whereas an on/off ratio of 6 × 106 has been demonstrated in **Figure 5a, d** [38].

#### **2.3 Lubricants**

Applications corresponding to surface-functionalized-graphene show additive counterpart in lubricant oil refinery owing to progressing research field. Extremely large mechanical-flexibility, fine friction-reduction, greater surfacearea, and anti-wear-ability support enhancement in properties. In addition, Zhang et al. also observed oleic acid-modified graphitic nature lubricant [40]. Tribological properties were investigated by employing four-ball tribometer relevant to oily surface-modified graphene. **Figure 6a, b** illustrates lubricant optimized-graphene with contents (0.02–0.06 wt.%), exhibiting improvedfriction as well as anti-wear activity, 17% friction-coefficient whereas 14% wear scar-diameter respectively. Desired friction behavior has been elaborated by

#### **Figure 6.**

*Four-ball test results: (a) FC versus graphene concentration; (b) WSD versus graphene concentration; (c) schematic diagram of the tribological mechanism of graphene sheets as oil additives; (d) lubrication regime transition [40].*

proposed tribological activity as shown in **Figure 6c**. Graphitic protective-layer became prominent on each steel ball surface separately with less concentration, thereby introducing improved anti-wear performance. On the other hand, oily films become discontinuous with higher density that is considered responsible for antiwear-degradation properties. Lin et al. investigated (0.075 wt%) stearic with oleic-acid modified graphitic nature in oil tunes wear-resistance along with load-carrying machine efficiency [41]. Current reports also presented that alkylated graphitic organic solvents may show lubricant behavior to improve properties [42]. Alkylated-graphene with different alkyl-chain-length (Cn = 8, 12, 18) is synthesized by condensed medium reaction (alkylamine+SOCl2-activated GO). It was investigated through octadecyl amino-graphene mixed with hexadecane. In this case, reduced friction along with wear concentration (26% and 9%) was obtained compared with hexadecane.

#### **2.4 Nanofluids**

Loss of energy in the form of heat energy slows down performance of various instruments and mechanical technology. Instrument and machinery performance may be improved by using some fluids such as DI water, transformer oil, and heatsensitive fluids. Heat transfer capability of fluids is less enough caused by the deterioration of productivity and lifetime of equipment and machines and also electronic circuits. To prolong heat transfer efficiency, the addition of nanomaterials addition is increased in fluids that may further improve the efficiency. Baby et al. reported thermal conductivity that may be increased upto14% with temperature (25<sup>ο</sup> C) and deionized water is used as base-fluid showing fraction by volume of only 0.056% [43, 44]. Moreover, thermal conductivity is increased upto 64% at 50<sup>ο</sup> C but with same contents belonging to modified-graphene. Ghozatloo et al. observed 0.06 wt% functionalized-graphene may improve thermal-conductivity (14.2%) when treated in water (25<sup>ο</sup> C) [45]. Finally, thermal-conductivity is enhanced (18%) when the temperature is increased to 52<sup>ο</sup> C.

*Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

#### **2.5 Graphene-based transparent and flexible conductive films for displays and electrodes**

Graphene is incorporated into electronics field by employing transfer printing along with solution-based approaches. Chhowalla et al. [46] suggested an efficient approach for smooth deposition with effective control of reduced graphene oxide in the form of thin films having thickness like single-monolayer to several-layers ranging large areas. Optoelectronic properties are tuned over reasonable order of magnitude that presents potentially beneficial towards transparent semiconductors as well as semi-metals. The thinnest films show graphitic ambipolar-transistor behavior. However, thick films behave like graphitic semi-metals respectively [47, 48]. Consequently, suggested deposition in this approach offered new routes to translate fundamental properties relevant to graphene into viable devices. Furthermore, large-scale transparent electrode growth has been successfully presented by Hong et al. [49] In this work, chemical vapor deposition technique was employed on thin nickel films. Two methods were applied for the formation of films and thereby transferring also to arbitrary substrates. Graphene films exhibited sheet resistance as well as optical transparency at desired level respectively. Graphene monolayers were transferred to SiO2 substrates showing electron mobility at faster rate along with half-integer (quantum Hall effect). High-quality graphene was grown by CVD that presented better results as compared with mechanically cleaved graphene as illustrated in **Figure 7a**-**c**. Owing to extraordinary mechanical properties, graphene demonstrated macroscopic use upto maximum level, resulting in conducting electrodes and transparent electrodes in (flexible and foldable) electronics [50].

In addition, superior optical and electronic graphene properties i.e., high mobility, optical behavior, flexibility trend, and environmental stability are accounted for promising material attributing to applications towards photonic as well as optoelectronic fields. In this support, comprehensive literary work has been done favorable for graphene photonics, optoelectronics, and other applications were offered by Ferrari et al. [51]. From scientific contents included in the review clearly show graphene-based conducting films and graphene oxide (GO) based conducting films that were used in synthesis of various photonic with optoelectronic devices. Equipment such as inorganic and organic electrodes of dye-sensitized solar cells, light-emitting diodes as well as electrochemical cells, touch screens, graphene-based absorbers.

#### **Figure 7.**

*Synthesis, etching, and transfer processes for the large scale and patterned graphene films, (a) synthesis of patterned graphene films on thin nickel layers (b) etching using FeCl3 (or acids) and transfer of graphene films using a PDMS stamp (c) etching using BOE or hydrogen fluoride (HF) solution and transfer of graphene films.*

Graphene electrodes showing high-performance field-effect transistors have been fabricated by Kim et al. [52]. To optimize performance of devices, authors controlled work-function attached with graphene electrodes via functionalization of SiO2 substrate surface. NH2 may donate electrons that are considered terminated SAMs but they are induced n-doping strongly in graphene. On the other hand, CH3-terminated SAMs contributed neutralized p-doping that was strictly induced through SiO2-substrates. Resultantly, graphene electrode work function considerably changed. Moreover, SAMs were observed as pattern-able robust yield. Besides, output of work may also be used towards fabrication of various graphitic nature compounds that paved foundation of electronic as well as optoelectronic devices.

Graphene films indicate mechanical along with optical properties as compared with other transparent-thin-films, particularly in photonics and optoelectronics. However, as far as conductivity is concerned it is inferior as compared with conventional (ITO) electrodes having comparable transparency and resulting in lower performance of devices working on graphene-based transparent thin films. Ahn et al. [53] presented an effective method to overcome deficiency and to improve graphene films concerning performance towards electrostatically doping that was employed through ferroelectric polymer. Aforesaid graphene films showing ferroelectric polarization have been used for the preparation of ultrathin organicsolar-cells (OSCs). Graphene-based OSCs have explored superior efficiency as well as superior stability as compared with graphene-based OSCs that were chemically doped. Moreover, OSCs fabricated by ultrathin-ferroelectric-film act as substrate with few micrometer sizes, exhibited attractive mechanical flexibility as well as durability. In the last, these may also be rolled up into cylindrical shapes having 7.5 mm diameter size.

#### **2.6 Graphene-based separation membranes**

Graphene nanopores sheets are used as separation membranes emerging and covering various since theoretical studies that were presented by Král et al. [54]. They were labeled modified nanopores incorporated graphitic type monolayers thereby resulted from molecular dynamic-simulation providing superior realm of hydrated ions. The ions in a partly stripped state connected with hydration shells may penetrate through infinitesimal pores having diameter ∼5 Å, such as fluorine with nitrogen terminated-pores permit flow of Li<sup>+</sup> , Na+ and K+ like positive ions having ratio 9:14:33 systematically whereas negative ions are strictly prohibited. On the other hand, hydrogen-terminated pores accelerate F− , Cl− and Br− anions along with a specific ratio 0:17:33 rather it blocks cationic passage. Aforesaid nanopores may provide versatile promising applications, particularly towards molecular separation and energy storage devices respectively.

In addition, Jiang et al. [55] contributed the work that dealt with permeability as well as selectivity related to graphene sheets structured with nanometer-scale pores adopting density functional theory for necessary calculations. Researchers investigated superior selectivity order of magnitude that was 105 for H2/CH4 showing excellent performance from H2 side in the situation of nitrogen-treated pore. Furthermore, report writers investigated selectivity at an extremely higher order of magnitude equivalent to 1023 for H2/CH4 for all hydrogen functionalized pores with width infinitesimally 2.5 Å, presenting a barrier (1.6 eV) for methane (CH4) whereas surmountable for H2 with magnitude 0.22 eV. These results exhibited that pores are considered superior to polymers as well as silica membranes. Whereas bulk solubility along with diffusivity is plays a dominant role to transport gas molecules throughout the material. Outcomes suggested one atom thin

#### *Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

porous-graphene-sheets behave such as highly efficient and selective membranes relevant to gas separation. Aforesaid types of pores may occupy a widespread impact concerning various energy devices with technological applications.

The molecular-dynamic-simulation employed by Xue et al. [56] explored CO2 separation strategy from that of CO2 mixture whereas N2 gas through porous graphene-membranes. Graphene sheets are chemically functionalized to observe its effects while porous graphene membranes performance for separation has been controllably examined. Researchers investigated chemical functionalization of graphene sheets that may increase absorptive capability of CO2 gas. On the other hand pore-rim chemical-functionalization significantly enhanced CO2 selectivity over N2 gas molecules. The results demonstrated versatile use of functionalizedporous-graphene for CO2 as well as N2 separation. Resultantly authors suggested an effective strategy, improving gas separation activity of porous-graphenemembranes [57].

Nanoporous graphene use for water desalination has been suggested by Grossman et al. [58]. Through employing classical-molecular-dynamics, this work presented nanometer-scale porous single-layer-graphene that may prove filter of (NaCl) effectively from that of water. Furthermore, authors researched desalination-performance corresponding to membrane exploring functioning of poresize, chemical-functionalization as well as applied-pressure. The results indicate membrane's ability that prevents salt penetration and all depends on the porousdiameter size along with sized pores suitable for water flow whereas passage of ions was banned. Further investigation indicates role of functional-groups appeared at graphene-edges in hydroxyl group may form commonly double hydrophilic nature. However, water flux is increased taking place by the reason of salt rejection activity with less amount corresponding to capability of hydroxyl group substituting water molecules in hydration-shell of ions. Collective and achieved outcomes that explored water-permeability of relevant material were clearly in higher magnitude as compared with reverse-osmosis membranes conventionally, thereby NPG may perform valuable role play towards water refinement [59, 60].

The same period was covered by Karnik et al. [61] study also who selectively suggested transport of molecules employing intrinsic-defects single-layer (CVD) graphene. In this case, small measured area was identified greater than 25 mm2 , but in turn it was transferred on porous polycarbonate-substrate. The collective contribution of pressure-driven as well as diffusive- transport with precise-measurement presented confirm evidence with respect to size-selective- transport of material molecules passing through membranes. They were attributed to low-frequency presence within 14 nm range diameter size pores relevant to (CVD) graphene as describe in **Figure 8**. Consequently, authors have proposed first step towards the occurrence of graphene-based selective- membranes [62–65].

Previous work was progressively continued [66] for molecular-sieving by employing porous- graphene. In this respect, Bunch et al. [67] also fabricated valves to control gas-phase-transport through graphene containing discrete nano-sized pores. Reports have revealed and identified gas-flux passing through discrete nanosize pores present in monolayer-graphene that may be detected as well as controlled employing nanometer-size gold clusters. These clusters are centered on graphene surface by migrating pores but partially block them also. However, samples containing not gold-clusters indicate stochastic-switching of magnitude of gas molecules attributing rearrangement of desired pores. Additionally, previously fabricated molecular valves may be involved particularly to progress ideal approaches towards a molecular synthesis that are considered foundation for controllable switching concerned with molecular gas flux [68, 69].

#### **Figure 8.**

*(a) Graphene composite membrane (GCM) consists of large-area graphene on polycarbonate track etch (PCTE) membrane, (b) permeability of the CVD graphene, KG, calculated for the three membranes using a simple circuit model (inset), indicated as a function of the diameters of the molecules. Only two pores, one of which is covered by graphene, are shown for clarity. The gray region denotes the continuum model prediction for graphene of porosity between 0.025% and 0.15% [61].*

#### **2.7 Biosensors**

Sensors are regarded as those devices that may identify changes in occurring events. Various studies have reported CNTs to use concerning sensors such as chemical, thermal, biological, and gas respectively. In addition, CNTs may also behave like flow sensors [70, 71]. It has been observed that liquid flow on SWCNTs bundles creates voltage normally in flow direction, and may be used in near future in the form of micro-machines working in a fluid medium, for example, heart pacemakers working without heavy-battery as well as recharging [70]. Piezoresistive sensors based on pressure may be prepared using CNTs. SWCNTs have also grown on polysilicon membranes [72]. Uniform pressure creates change into resistance of SWCNTs that was observed in membranes. From viewpoint of Caldwell et al. [73] piezoresistive fabrication offered pressure sensors for CNTs that may bring changes dramatically to biomedical industry and various piezoresistance diagnostic nature as well as therapeutic devices have recently applied in sensor field. Moreover, CNTs fabricated biosensors are used to detect deoxyribonucleic acid concentration in the body. Aforesaid instruments also detected specific parts of DNA corresponding to particular type of disease [74]. Sensors previously mentioned become capable to detect only few molecules of DNA containing specific sequences, thereby increasing probability to diagnose patients possessing specific sequences that are closely related to cancerous genes. Furthermore biosensors have been suitably used for the sensing of glucose. CNTs chemical-sensors, especially for liquids, may also use sensing capability to investigate blood completely or partially. In this case, biosensors are proposed favorable to detect sodium as well as to find pH value accordingly [75].

Having small size with owing attractive electrochemical properties, carbon nanotubes contribute a great part as a component of biosensors. Additionally, CNTs fabricated electrodes possess interesting electrochemical properties as compared with previously available electrodes and show superior quality [76]. CNT-based biosensors present a high aspect-ratio that enables tubes to become embodied into proteins so that electron transferring included with enzymes frequently occur such as glucose oxidase where redox centers are observed not normal to be accessible (See **Figure 9**) [78]. Moreover, chemically modified CNTs have become an effective approach to contribute selectivity property into resulting biosensors that have sufficiently exploited towards exploring sensitivity to detect DNA molecules [79]. However, in near future, fine efforts may be expected to direct towards preventing biomolecules that may be absorbed on surface of tube walls, whereas promising advances have previously contributed a great part in this respect [80]. Further

*Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

#### **Figure 9.**

*Schematics of synthesis process DNA based biosensors [77].*

advancements may extend range of molecules to be modified that are considered attachable to nanotubes whereas enzymes, as well as nucleic acids along with some metal nanocrystals, are numerously employed to meet the need so far. Particularly respect is electropolymerized coatings have been appreciated that may be prepared with various concentrations, having precise and controllable thicknesses [81].

#### **2.8 Fuel cells**

As far as fuel cells are concerned, they are utilized for conversion of chemical energy into electricity directly with great efficiency and exhibited excellent results towards different applications [82–84]. In the fuel cells, catalysts on membrane surface are especially PEM made from graphene. Recently numerous investigations are under progress assessing probability for substitution of platinum catalyst with metals or metal oxides and with nitrogen functionalized metal catalyst [85, 86]. However, some catalysts face issues such as stability as well as activity as compared with platinum catalyst. Active carbon exhibits capability for meeting said challenges yet they tend to occupy certain limitations accordingly. They possess high surface area owing to have instability thereby raising major issues unless coupled with suitable material for this purpose. Graphene technological development made by active carbons has suggested stronger substitutes to platinum occupying high conductivity whereas surface area is considered high along with adhesion property for the catalyst [87, 88]. Graphene oxide, a derivative of graphene resides large number of functional groups making them best for nucleation sites such as catalyst nanoparticles randomly locate on and edges of the surface [89]. The extensive use of graphene is indicated in fuel cells showing supporting material to anode catalyst and replace also cathode catalyst as well as standalone electrolyte membrane and bipolar plates. All work may be summarized concerning role of graphene in various component forms. Platinum, as well as alloys, are supposed as conventional catalysts in the electrodes of fuel cells. They are either an anode or cathode located in fuel cells. These fuel cells are fed by hydrogen and other hydrocarbon methanol [90] as well as ethanol [91]. Platinum is expensive as well as limited in availability and also caused by the produced intermediates while oxidation reactions are carried out at different fuels [92]. Various approaches were employed to reduce catalyst loading or complete replacement of Pt catalyst by using non-precious catalyst reactions at anodes [93] as well as cathode [94] terminals of fuel cells.

#### **2.9 Supercapacitors**

Supercapacitors harvest excellent properties such as energy density, ultra thinness, and long life, and therefore have proven promising candidates in

electrochemical energy-storage systems [95–97]. Initially, supercapacitors may be categorized into electrical double-layer as well as Pseudo-capacitors depending on energy-storage mechanisms. In first category, charges accumulate electrostatically at electrode and electrolyte interface through formation of an electrical doublecharges layer. Charge-storage is uniquely physical essence showing no chemical reaction yet is called non-faradaic process. Electric-double-layer behaves like dielectric whereas capacitance proves direct-function owing to surface-area of electrode. Therefore, carbon-based nanomaterials possessing great surface-area for electrodes increase capacitance of electrical double-layer capacitors. Charge –discharge functioning is indicated by ion absorption-desorption capability of EDLC. Ions are directed forming EDL at the time of voltage application at electrodes which in turn charge EDLC for controlling purpose. It has been observed that carbonaceous electrodes exhibit fine electrochemical surface-area inheriting large porosity caused by creating enhanced interfacial-area forming prominent EDL. Carbonaceous materials have attractive electrical properties owing to which are labeled as basic type of EDLC [98]. Unlike EDLC nature, Pseudo capacitors show capability of fast (Faradaic) charging with transfer-reactions that are carried out at solid electrodes as well as electrolytes. As a result, faradaic-charge-transfer is an applied voltage-dependent system. Fundamental electrochemical reactions in pseudocapacitance involve chemisorption along with electro-sorption from electrolyte. Redox (oxidation and reduction) reactions attractions from electrolyte thereby producing intercalation/de-intercalation sites relevant to active electrodes. Previous electrochemical processes are proposed as surface dependent. In order to promote electrochemical properties attributing to capacitors, great efforts were devoted to making functionalization/hybridization related to a variety of materials or nanostructured optimized promising candidates [99].

#### **3. Conclusions and future directions**

Advanced carbons materials such as graphene and CNTs are considered key merits for affordable energy conversions and storage versatile applications. The investigation explored the latest technological advancement during synthesis of the said advanced materials whereas characterizations are performed with respect to current day applications. CVD technique often leads to production of nanostructures having porous networks showing good conductivity. Since quality improvement is the main goal of research work of relevant material, so is improved significantly through employing such technique. Growing concerns are also expected concerning scalability adopting this approach reasonably. Furthermore, characteristics and performance are achievable towards graphene as well as graphene oxide equally growing concern size with quality of grapheneoxide-precursor. The investigation related to novel techniques are aimed to enhance into inter-sheet- binding is considered another novel direction towards research purpose. Desired characteristics are proposed to be achieved through merging graphene sponges as well as polymers. As far as research-based graphene applications are concerned, they belong to several energy storage/conversion devices that are considered still novel in research activities. Graphene suitability has exhibited electrochemical properties prominently and for electrochemical purposes accordingly.

Peculiarities related to graphene as well as graphene oxide compared to allotropes of carbon were also discussed in detail. Aforesaid merits include such as excellent surface-area, high conductivity, great solubility, facile synthesis, and cheap source material as well. Though various technological advancements were explored yet space is available for improvement particularly for both

*Advanced Carbon Materials: Base of 21st Century Scientific Innovations in Chemical, Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95869*

electro-analytical and electrochemical sensors. Some of other electrochemical applications related to graphene oxide are still extendable covering further electrochemical applications towards future directions. Furthermore, critical challenges are still associated with such material as facile synthesis has been critically addressed. The structure of graphene oxide is also still incomplete at molecular level and therefore considered more important in literature. Other focus areas are supposed to be an understudy for further attention with respect to defects concerned with conductivity of graphene oxide. A brief understanding of electron flow on graphene oxide substrate/interface will also be an empty area of research available for further enhancement towards graphene oxide as well as other applications. Designs and approaches adopted, up till now, associated with manufacturing of graphene oxide devices are suggested critical in the future status of this material. Despite the aforementioned and highlighted challenges, graphene oxide applications associated with electrochemical sensors remain the key future application of graphene oxide.

## **Author details**

Muhammad Ikram1 , Ali Raza<sup>2</sup> , Khurram Shahzad3 , Ali Haider4 , Junaid Haider5 , Abdullah Khan Durrani3 , Asim Hassan Rizvi3 , Asghari Maqsood6 and Mujtaba Ikram3 \*

1 Solar Cell Applications Research Lab, Department of Physics, Government College University Lahore, Punjab, Pakistan

2 Department of Physics, Riphah Institute of Computing and Applied Sciences (RICAS), Riphah International University, Lahore, Pakistan

3 Institute of Chemical Engineering and Technology (ICET), University of the Punjab (PU), Lahore, Punjab, Pakistan

4 Department of Clinical Medicine and Surgery, University of Veterinary and Animal Sciences, Lahore, Punjab, Pakistan

5 Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China

6 Nanoscale Laboratory, Department of Physics, Air University, Islamabad, Pakistan

\*Address all correspondence to: mujtaba.icet@pu.edu.pk

© 2021 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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## Section 2
