*3.1.4 Carbon fibers/CNTs*

A novel method was studied to graft carbon nanotubes over carbon fiber to form a CNT/CF [49]. Islam reported direct covalent bonded CNTs and CF without any catalyst or coupling agents through ester linkage. CNTs can be used to reinforce CFs to improve interfacial shear and impact strength [50]. Two methods are reported to attach CNTs with CF by physical adsorption (Van der waals interaction), which are weaker than chemical covalent bonding [51].

#### **3.2 Graphene-based nanocomposites**

Graphene-based nanostructured materials have distinctive 2D structures with high electronic mobility, exceptional electronic and thermal conductivities, excellent optical performance, good mechanical strength, and ultrahigh surface area as compared to other materials.

#### *3.2.1 Polymer/graphene nanocomposite*

Graphene nanofiller addition within the polymer has a promising application in biosensors, energy storage devices, photocatalysts, drug delivery. Recently, a wide range of processing methods has been studied for scattering both GNP and GO-derived fillers into polymer matrices. Controlled amount of nanomaterial by weight % and size is carefully taken into deliberation [52]. Salimikia et al. [53] synthesized a solid-phase microextraction fiber over polyaniline/graphene oxide nanomaterial using the electrospinning method and used it as sorbent for determination of nicotine. Farajvand et al. [54] prepared Graphene oxide/polyaniline nanocomposite and used it as an adsorbent to determine cadmium (II) ions in an aqueous solution.

#### *3.2.2 Activated carbon/graphene nanocomposite*

Activated carbon is considered as the center of research for commercial utilization. Adsorption properties of metal ions by AC/GR have been examined and a number of methods have been developed for synthesis of graphene/activated carbon nanosheet composite to make high-performance electrode material for supercapacitors. Many research groups have used activated carbon for preparation of graphene nanocomposites. Xin et al. [55] reported a new carbon nanocomposite material having graphene and activated carbon and used it for oxygen electrode (cathode) in Li-ion batteries. In the AC/GR, the graphene showed a three-dimensional (3D) arrangement having good electrical conductivity and exceptional mechanical strength and elasticity, while the AC coating on the graphene surface supplied several meso/micropores with diameters less than nanometers. Lu et al. [56] investigated an easy method to prepare a new catalyst by electrodepositing of Ag nanocrystals on the different polymer dyes, Poly (methylene blue) or Poly (4-(2-Pyridylazo)-Resorcinol) modified graphene carbon spheres (GS) hybrids which had advantages of both carbon spheres and graphene composite and were employed for detection of H2O2 as nonenzymatic electrochemical sensor. Hossain and Park [57] studied the hydrothermal method for the synthesis of glucose-treated reduced graphene oxide-activated carbon composites. Platinum nanoparticles were electrochemically deposited on a modified composite surface. Chitosan-glucose oxidase composites and Nafion were incorporated into modified surface of working electrode for the preparation of an extremely sensitive glucose sensor.

#### *3.2.3 Metal oxide/graphene nanocomposite*

In this type of nanocomposites, metal oxide particles are incorporated in graphene nanosheets. Metal oxide-based Graphene nanocomposite has attained the attention of scientific community as anode materials due to high kWh/cost and effective highperformance electrode material in an electrochemical supercapacitor. Beura et al. [58] prepared ZnO-based graphene nanocomposites by hydrothermal method and used it

#### *Improved Nanocomposite Materials and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.102538*

as a catalyst for the degradation of dyes. The band of the nanocomposites was 2.84 eV, while the photoluminescence lifetime increased from 15.05 to 21.60 ns. Photocatalytic activity of the composite material was investigated by both anionic and cationic dyes. Borah et al. [59] used an in-situ method to synthesize TiO2/rGO. The prepared nanocomposites were used to catalyze the transesterification of waste cooking oil into biodiesel. Excellent catalytic activity was shown by the catalyst and 98% conversion of oil into biodiesel was seen at optimum reaction conditions. Wang et al. [60] presented a detailed summary of the research progress on the low-cost metal oxides/ graphene nanocomposites (MOs/G) as anode materials for SIBs.

#### *3.2.4 Metal/graphene nanocomposites*

Various heavy metals such as Au, Fe, Cu, Ce, etc., have been introduced into graphene nanosheets to form different nanocomposites. Nanocomposite with ultra-low resistivity than conventional copper metal at room temperature is the next generation conductor. Several research groups have fabricated metals/ graphene nanosheets. Arukula and co-workers [61] prepared rGO/polyaniline (PANI)/Pt–Pd nanocomposite by wet reflux strategy. The prepared nanocomposites materials were used as potential anode catalysts with improved methanol oxidation tendency for direct methanol fuel cells (DMFCs). Xuan et al. [62] reported a 3D patterned porous laser-induced silver-based graphene nanocomposite. The prepared nanocomposites were used as an electrode, which showed high, uniform electrical conductivity even under mechanical deformations. Incorporation of platinum and gold nanoparticles on the 3D porous LIG importantly enhanced the electrochemical capacity for wearable glucose sensor applications. Zheng et al. [63] reported the quick and effective preparation and characterization of a novel nitrogen-doped graphene copper nanocomposite. The prepared nanocomposite showed superior electrical conductance of 538 W/m·K at room temperature, which is 138% greater than that of copper. The measured electrical resistance was 0.16 μΩ cm at 25°C which is much lower than that of copper. Gupta et al. [64] reported copper-based reduced graphene oxide nanocomposite for use as a catalyst. The copper-based reduced graphene oxide catalyst was easily recovered and used for seven consecutive cycles.

#### *3.2.5 Fibers/graphene nanocomposites*

In this type of nanocomposites, graphene is used as a filler while fibers are used as a matrix. Davoodi and co-workers [65] reported the preparation of polylactic acid and GO-based nanocomposite using the electrospinning method. The mechanical properties, surface chemical structure, and topology study of the nanofibers were performed. Jin et al. [66] used a facile method for the hybridization of polyaniline nanofibers (PANI NFs) on functionalized reduced graphene oxide (FrGO) films. The GO was first reduced and functionalized by sulfur to form FrGO. Hydrothermal method was used to hybridize FrGO and PANI NFs to form PANI NFs/FrGO composite films. The as-prepared nanocomposite films were uniform, flexible, and stable with a high specific capacitance of 692.0 F/g at 1 A g−1 and excellent capacitance retention of 53.5% at 40 A g−1. Wan et al. [67] used a facile two-step method to prepare a ternary flexible nanocomposite material of bacterial cellulose/graphene/ polyaniline (BC/GE/PANI). The prepared nanocomposite showed enhanced electrical conductivity of 1.7 ± 0.1 S/cm, which is greater than most of the polyaniline-based composites.


#### **Table 1.**

*Comparison of mechanical properties of different polymers and their nanocomposites [68].*

**Table 1** shows the comparison of mechanical properties of some polymers and their nanocomposites.
