Characterization and Application of Nanomaterials (2023) Volume 6 Issue 1 doi:10.24294/can.v6i1.2637 1 Review Article High-tech graphene oxide reinforced conducting matrix nanocompo- sites—Current status and progress Ayesha Kausar1,2,*, Ishaq Ahmad1,2, Tran Dai Lam3 1 NPU-NCP Joint International Research Center on Advanced Nanomaterials and Defects Engineering, Northwestern Polytechnical University, Xi’an 710072, Shanxi Province, China. E-mail: dr.ayeshakausar@yahoo.com 2 UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, iThemba LABS, Somerset West 7129, South Africa. 3 Institute for Tropical Technology, Vietnam Academy of Science and Technology, Hanoi 100000, Viet Nam. ABSTRACT Graphene oxide can be referred to as oxidized graphene. Similar to graphene, oxidized graphene possesses remark- able structural features, advantageous properties, and technical applications. Among polymeric matrices, conducting pol- ymers have been categorized for  conjugated backbone and semiconducting features. In this context, doping, or nano- additive inclusion, has been found to enhance the electrical conduction features of conjugated polymers. Like other carbon nanostructures (fullerene, carbon nanotube, etc.), graphene has been used to reinforce the conjugated matrices. Graphene can be further modified into several derived forms, including graphene oxide, reduced graphene oxide, and functionalized graphene. Among these, graphene oxide has been identified as an important graphene derivative and nanofiller for con- ducting matrices. This overview covers essential aspects and progressions in the sector of conjugated polymers and gra- phene oxide derived nanomaterials. Since the importance of graphene oxide derived nanocomposites, this overview has been developed aiming at conductive polymer/graphene oxide nanocomposites. The novelty of this article relies on the originality and design of the outline, the review framework, and recent literature gathering compared with previous liter- ature reviews. To the best of our knowledge, such an all-inclusive overview of conducting polymer/graphene oxide fo- cusing on fundamentals and essential technical developments has not been seen in the literature before. Due to advanta- geous structural, morphological, conducting, and other specific properties, conductive polymer/graphene oxide nano- materials have been applied for a range of technical applications such as supercapacitors, photovoltaics, corrosion re- sistance, etc. Future research on these high-performance nanocomposites may overcome the design and performance- related challenges facing industrial utilization. Keywords: Graphene Oxide; Conductive Polymer; Nanocomposite; Conductivity; Supercapacitor 1. Introduction Conductive, conducting, or conjugated polymers constitute an es- sential category of polymers with semiconduction or electron conduction properties[1,2]. Important types of conjugated polymers include polya- cetylene, polyaniline, polythiophene, polypyrrole, and derivatives. Con- jugated polymers have been recognized for their optical, electrical, thermal, and physical characteristics[3]. Technological applications of conductive polymers have been observed for electronics, energy de- vices, biomedical fields, and so on[4]. Graphene is a one-atom-thick two-dimensional nanosheet material[5]. Graphene oxide is simply a gra- phene derivative having oxygen-containing surface functionalities on graphene nano-sheet. Graphene oxide has been utilized to form polymer nanocomposites with conducting polymers, thermosets, and thermo- plastic matrices[6,7]. Particularly conducting polymers are generally ARTICLE INFO Received: 30 April 2023 Accepted: 13 June 2023 Available online: 24 June 2023 COPYRIGHT Copyright © 2023 by author(s). Characterization and Application of Nano- material is published by EnPress Publisher LLC. This work is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ 2 well-known due to their remarkable properties, such as low price, high conductivity, lightweight- ness, simple fabrication, and reusability potential. Doping of conducting polymers on graphene oxide surfaces usually leads to interface formation, which improves the electrical properties of the resulting nanocomposite[8]. Due to interface development between matrix-nanofiller, charge transfer across the interface is greatly promoted. Consequently, these nanocomposites possess fine durability, con- ductivity, corrosion resistance, mechanical strength, wear resistance, and barrier properties[9]. Several approaches have been used for the fabrica- tion of conductive polymer/graphene oxide nano- composite, including in situ, solution, electro- polymerization, electrodeposition, etc.[10]. Conse- quently, conducting polymer and graphene oxide derived nanocomposites revealed suitability for ap- plication in technical sectors such as photovoltaics, capacitors, sensing devices, radiation shielding, etc.[11–13]. Therefore, the major theme behind devel- oping this review article is to gather and portray the field literature and efforts reported on graphene ox- ide reinforced conducting polymer nanocompo- sites so far, in a novel way by identifying the prop- erty/potential advantages of combining conducting polymers with graphene oxide nanofiller. Hence, this overview is designed to cover in- dispensable properties and potential aspects of gra- phene oxide reinforced conductive polymer nano- composites. Owing to the unique structural combi- nation of conjugated polymer and graphene oxide, essential features of the conductive nanomaterials have been enhanced. Subsequently, conducting polymer and graphene oxide-based nanocompo- sites were investigated, aiming for energy storage and production devices and anticorrosion nano- materials. 2. Graphene oxide Graphene is a nanocarbon nanoallotrope with sp2 hybridized carbon atoms in nanostructure[14]. It is a monolayer of carbon with hexagonal arrange- ments. Graphene is simply a single sheet of stacked graphite nanostructure[15]. Graphene is a one-atom- thick nanosheet of carbon atoms[16]. Due to hybrid- ization and π electron conjugation, the graphene nanosheet reveals semiconductivity features[17]. Graphene has been prepared using a number of top- down and bottom-up techniques, such as graphite chemical or mechanical exfoliation, chemical va- por deposition, plasma-based chemical vapor dep- osition, thermally enhanced chemical vapor depo- sition, laser ablation, organic synthesis, and other important techniques[18]. Graphene oxide is a sig- nificant modification of the graphene nanosheet through the incorporation of various surface func- tionalities[19]. Mainly hydrophilic groups like car- bonyl, acid, epoxide, hydroxyl, etc. have been ob- served on the graphene oxide nanosheet. Figure 1 gives a comparison of the simple structures of gra- phene vs. graphene oxide. Hummer’s approach and the Brodie method have been commonly used for the formation of graphene oxide[20,21]. Both of these methods involve using oxidizing agents for the for- mation of graphene oxide from graphene[22]. Gra- phene oxide possesses high conductivity, heat sta- bility, mechanical strength, and chemical stability features. Graphene oxide has been essentially rein- forced in polymers to form nanocomposites. Poly- mer and graphene oxide derived nanomaterials have been applied for electronics, energy devices, membranes, and biomedics[23–25]. Figure 1. Graphene and graphene oxide. 3. Conducting polymers Conductive polymers have been placed in a separate category of polymers and are not included in thermoplastics or thermosets classifications[26,27]. Inherently conducting polymers have conductivity properties similar to semiconductors[28]. Therefore, conducting polymers are often referred to as syn- thetic metals[29]. Conductive polymers have light 3 weight and fine processability properties[30]. The π- conjugation in conducting polymer backbones formed an electron transportation system and elec- tron affinity properties[31]. The presence of alter- nate single and double bonds in conducting poly- mers causes delocalization of electrons in sp2 hy- bridized orbitals. Consequently, conductivity prop- erties are actually due to electron transportation through double bonds and charge transfer by reso- nance. Doping agents and oxidation-reduction pro- cesses were applied to enhance the conducting characteristics of conductive polymers. Polyacety- lene is an intrinsically conjugated polymer[32]. The doping process has been used to improve the elec- trical conductivity features of polyacetylene[33]. Other significant conductive polymers are poly- carbazole[34], polythiophene[35], polypyrrole[36], polyaniline[37], and several derived forms (Figure 2). HN Polyaniline Polypyrrole N S Polythiophene Poly(3-hexylthiophene) n n n S n Figure 2. Some significant conjugated polymers. Among these, polyaniline is the most widely studied conductive polymer. Polyaniline is a low- priced and easily possessable conjugated poly- mer[38]. Polyaniline has been studied for electron transportation and percolation threshold values. Consequently, conducting polymers have high electron conductivity and technical applications. 4. Graphene oxide nanofiller in conducting polymeric nanocompo- sites Graphene and graphene oxide nano-reinforce- ments have been used to form polymeric nanocom- posites[39]. Graphene derivative nanofillers have improved the electronic, strength, heat stability, and other features of the resulting nanocompo- sites[40]. However, graphene and derivatives can have poor dispersion in matrices because of the wrinkling effect. Graphene oxide possesses the ad- vantage of better dispersion in polymers due to its surface functionalities[41]. Moreover, graphene ox- ide has been found to develop better interactions with the polymer matrix. Appropriate processing approaches need to be adopted for fine graphene oxide dispersion in polymer matrices[42]. Con- sistent graphene oxide dispersion in matrices has been found to enhance the electron conductivity, heat constancy, robustness, and physical features of the nanocomposites. In this context, conductive polymers have been filled with graphene oxide nanofiller to design efficient nanocomposites[43]. Polyaniline (an important conjugated polymer) and graphene oxide derived nanocomposites have been fabricated[44]. Li et al.[45] applied in situ polymerization for the development of polyaniline and reduced graphene oxide based nanocomposites. Gao et al.[46] also formed polyaniline and reduced graphene oxide based nanocomposites through in situ techniques. The reduced graphene oxide was produced by sodium borohydride. Chauhan et al.[47] fabricated polyaniline and reduced graphene oxide derived nanocomposites. Increasing reduced gra- phene oxide contents led to enhancements in elec- tron conduction and specific capacitance properties. Graphene oxide was functionalized with sulfonic acid for modification. Consequently, the polyani- line and sulfonated graphene oxide revealed fine electron conduction features. Hawash et al.[48] fab- ricated polyaniline and graphene oxide nanosheet- immobilized granular tea waste-derived nanocom- posites. The nanomaterial has been applied for ef- fective removal of bromide (Br−) from aqueous systems. The nanocomposite revealed bromide ad- sorption of 26.8 mg–1. Figure 3 shows an oxidation technique to form the polyaniline/graphene oxide nanosheet-immobilized granular tea waste nano- composites. Graphene oxide functionalities have been found to interact with the functional groups on granular tea waste, such as carboxylic acid, hy- droxyl, amine, amide, etc. Consequently, electro- static as well as hydrogen binding interactions were developed to form the nanocomposite. 4 Figure 3. Schematic for the formation of PANI/GO@GTW nanocomposite[48]. PANI = polyaniline; GO = graphene oxide; GTW = granular tea waste; PANI/GO@GTW = polyaniline/graphene oxide nanosheet immobilized granular tea waste[48]. Reproduced with permission from MDPI. Polypyrrole is a significant conductive matrix with facile preparation and electrical conductivity features[49]. Several designs have been formed us- ing polypyrrole and graphene nanofiller[50]. Simi- larly, polypyrrole and graphene oxide derived na- nomaterials have been reported[51]. Graphene oxide dispersion has been used to enhance the physical properties of the polypyrrole nanocomposites, such as electron mobility and thermal transport[52]. These nanocomposites have been developed using in situ, electrochemical, emulsion, and solution polymerization techniques. Deng et al.[53] devel- oped polypyrrole and graphene oxide based nano- composites by the electrochemical synthesis method. The inclusion of 0.5 to 1 wt.% graphene oxide led to an impedance variation of 115 to 26 kΩ. Wu et al.[54] prepared polypyrrole, reduced graphene oxide, gold nanoparticles, and glucose oxidase based multilayered films through the elec- trodeposition method. Figure 4 illustrates the step- wise synthesis process for the formation of polypyrrole/reduced graphene oxide/gold nanopar- ticles/glucose oxidase nanocomposite. Initially, the biosensor was synthesized through the electrodep- osition of polypyrrole/reduced graphene oxide on a neat glassy carbon electrode. Then, gold nanopar- ticles and glucose oxidase were immobilized on the electrode surface. The glucose oxidase formed self- assembly along with gold nanoparticles on the polypyrrole/reduced graphene oxide nanocompo- site surface. Gold nanoparticles can efficiently bond to biomolecules such as enzymes or nucleic acids via covalent linking. Figure 5 depicts cur- rent-time curves using a glucose biosensor based on polypyrrole/reduced graphene oxide/gold nano- particle nanocomposite in the applied potential range of 0.35 V to 0.55 V. It has been observed that increasing applied potential increases the current values. For the biosensor, a working potential of up to 0.5 V was used to attain high selectivity or sen- sitivity. The nanocomposite electrode was found to be efficient in detecting glucose in the range of 0.2 to 8 mM. The detection limit was found to be 5.6 μM. In addition, biosensor was found to has eco- friendly properties. Figure 4. Schematic illustration of a glucose biosensor using the polypyrrole and reduced graphene oxide (PPy-RGO) and gold nanoparticles and glucose oxidase (AuNPs-GOD) multi- layer films as the sensitive layer fabricated by the electrodep- osition and self-assembly[54]. AuNPs = gold nanoparticles; GOD = glucose oxidase; PPy- RGO-AuNPs/GOD = polypyrrole/reduced graphene ox- ide/gold nanoparticles/glucose oxidase. Reproduced with per- mission from MDPI. 5 Figure 5. Current-time curves for PPy-RGO-AuNPs- GOD/GCE in 4 mM glucose at different applied potentials from 0.35 V to 0.55 V versus SCE[54]. PPy-RGO-AuNPs/GOD = polypyrrole/reduced graphene ox- ide/gold nanoparticles/glucose oxidase/electrode. Reproduced with permission from MDPI. Polythiophene and derived forms have been utilized to form nanocomposites[55]. Shamsayei et al.[56] fabricated polythiophene and graphene oxide based nanocomposites by the electrochemical method. The microstructure and electron conduc- tion features of the nanomaterials have been ex- plored. Bora and researchers[57] used the interfacial polymerization method for the formation of poly- thiophene and graphene oxide based nanomateri- als. Due to nanofiller loading, dispersion, and the formation of a percolation network, the nanocom- posite had a high electrical conductivity of 2.7 × 10–4 S cm–1. Thermal stability analysis revealed higher degradation temperatures in the range of 248–260 ℃ for the nanocomposites relative to the neat matrix (200–300 ℃). Yang et al.[58] fabricated poly(3-hexylthiophene) and reduced modified gra- phene oxide based nanocomposite. The morphol- ogy studies were performed to study the nanoparti- cle dispersion in the matrix. The poly(3-hexylthio- phene) was found layered on the nanofiller surface. Pilo et al.[59] used a polythiophene derivative, poly(2,5-di(2-thienyl)thieno[3,2-b]thiophene, with graphene oxide to form the nanocomposites. The resulting nanomaterials have been utilized for the formation of enzyme-sensing electrodes. The bio- sensor had a detection limit and sensitivity of 0.036 mM and 9.4 µA mM–1 cm–2, respectively. Zamani et al.[60] fabricated the poly(3,4-ethylenedioxythio- phene)/graphene oxide nanocomposite. The mate- rial was electrodeposited on solid phase microex- traction fiber to form the sensing electrode. The nanocomposite electrode had a detection limit of 0.005–0.025 µg L–1 for tricyclic antidepressants (nortriptyline, amitriptyline, desipramine, imipra- mine, etc.). The sensing electrode revealed drug extraction of up to 105%. 5. Significance of graphene oxide filled conducting nanocomposites Supercapacitors have been categorized as ef- fective energy storage devices[61]. Conductive pol- ymers and derived nanocomposites have been ap- plied to form supercapacitors[62]. Polythiophene has been effectively used in supercapacitors owing to efficient charge mobilization, eco and chemical stabilization[63]. Moreover, polythiophene and gra- phene oxide derived nanocomposites have been functional for supercapacitance application[64]. Mostly, in situ polymerization route was adopted to attain polythiophene/graphene oxide nanocom- posite for supercapacitors. The poly(3,4-ethylene- dioxythiophene) nanocomposites filled with gra- phene oxide possess a high specific capacitance of about 201–320 Fg–1[65]. The poly(9-butyl-3,6- di(thien-2-yl)-9H-carbazole) and graphene oxide based nanocomposite also have a specific capaci- tance of up to ~320 Fg–1[66]. Interactions among polythiophene or polythiophene derivatives and graphene oxide occur via non-covalent bonding and π-π stacking interactions. These interactions have improved electron transfer, specific capaci- tance, and charge-discharge performance[67,68]. Zhou et al.[69] formed polypyrrole and graphene ox- ide derived nanocomposite through an electro- chemical approach. The nanocomposite was elec- trochemically co-deposited on the fluorine doped tin oxide substrate. Then, the layered supercapaci- tor was formed by sandwiching the nanocomposite layer between the fluorine-doped tin oxide sub- strates. Li et al.[70] developed cellulose and gra- phene oxide based nanocomposites. Then, polyan- iline was layered on cellulose/graphene oxide through in situ polymerization of aniline mono- mers. Cellulose/graphene oxide/polyaniline nano- material possess a high electron conduction of about 1.15 S cm–1. The supercapacitor electrode had a sufficiently elevated specific capacitance of 6 1,218 mF cm–2 at 1.0 mA/cm2. The flexible super- capacitor electrodes have revealed constant capac- itance with twisting, so they can be used for flexi- ble electronics. Figure 6 shows a schematic for the formation of nanocomposite. Moreover, the con- tact behavior of water droplets on nanocomposite surfaces was studied for super wettability behavior. Due to the porous nature of the nanocomposite, a water droplet was easily penetrated. Figure 7 de- picts cyclic voltametric curves for in series and par- allel devices as compared to a single device. The supercapacitor was used to light a red-light emit- ting diode for 4 minutes. Consequently, the nano- composites have been used to form flexible, weight-less electronics. Figure 6. (a) Synthetic route to cellulose/graphene oxide/pol- yaniline nanocomposites; (b) the water droplet contact pro- cess on the nanocomposite surface[70]. GO = graphene oxide; PANI = polyaniline; ANI = aniline; APS = ammonium peroxydisulfate. Reproduced with permis- sion from MDPI. Figure 7. (a) CV profiles of single device, two devices in se- ries, and two devices in parallel connection at a scan rate of 50 mVs–1; (b) GCD profiles of single devices and three de- vices in series at a current density of 2 mA cm–2; and (c) opti- cal pictures of three devices in series connection to light a LED lamp for 4 minutes[70]. CV = cyclic voltammetry; LED = light emitting diode; GCD = galvanostatic charge/discharge. Reproduced with permis- sion from MDPI. Multipurpose energy production devices have also been focused on the use of conducting poly- mers[71]. In this context, conjugated polymers have been filled with efficient carbon nanoparticles such as fullerene, graphene, graphene oxide, and carbon nanotubes[72]. Ensuing nanocomposites have been used to improve solar cell efficiencies. Graphene oxide has been adopted as an efficient electron ac- ceptor nanomaterial in solar cells[73]. Graphene ox- ide has a large surface area and electron-conduct- ing pathways for electron passage through the ma- terial. Polythiophene and derivatives reinforced with graphene oxide have been integrated into solar cells[74]. Stylianakis et al.[75] fabricated and applied poly(3-hexylthiophene) and graphene oxide nano- materials for bulk heterojunction solar cells. Poly(3-hexylthiophene) was used for electron do- nation, whereas graphene oxide worked for elec- tron acceptance material[76,77]. Furthermore, gra- phene oxide formed a percolation network, allow- ing electron diffusion through the system[78]. Ag- bolaghi[79] produced the polyaniline and reduced graphene oxide nanomaterials through in situ tech- niques. The resulting nanocomposite has a solar cell efficiency of up to 7%. Corrosion is a critical issue for metal-based industries[80]. In this context, different methods have been developed and applied for the corrosion protection of metals, such as the use of inhibitors and surface coatings[81]. Conductive polymers were reinforced with graphene and graphene oxide to de- velop anticorrosion coatings[82]. Moreover, pristine graphene oxide has been used as the a corrosion protective coatings[83]. Graphene oxide has been layered on nickel or copper metal for corrosion in- hibition[84]. Similarly, graphene oxide reinforced polyaniline matrix has also been used as an anticor- rosion coating[85]. Graphene oxide filled polythio- phene nanocomposites have been applied for cor- rosion protection applications[86]. Electron conduc- tion and corrosion defiance features of polythio- phene/graphene oxide nanomaterials have been ex- plored. However, few research efforts have been observed regarding polythiophene and graphene oxide derived anticorrosion nanomaterials so far. 7 Therefore, further investigations are desirable in this field to attain better designs and properties[87]. 6. Prospects and conclusions Continuous research efforts have been fo- cused on conductive polymeric materials. Essential conjugated polymers such as polyaniline, polythi- ophene, polypyrrole, and derived polymers have been investigated with graphene oxide nanofiller. In this respect, various processing methods have been used to form the conductive polymer/gra- phene oxide nanomaterials. Consequently, struc- ture, microstructure, and electron transportation properties have been explored. Interactions be- tween conjugated polymers and graphene oxide have been found to enhance the features of the en- suing nanocomposites. Inclusion of graphene oxide has been reported to enhance the electrical conductivity of the con- ducting polymer up to 50–90%. Enhancement in electrical conductivity depends upon the nanofiller dispersion and interaction with the matrix, which may ultimately lead to the formation of an electron- conducting network for percolation[88]. Cheng et al.[89] reported the fabrication and electrical con- ductivity properties of polyaniline and graphene oxide derived nanocomposites. Inclusion of 0.45 wt.% graphene oxide in polyaniline led to an elec- trical conductivity of up to 9.8 S cm–1, which is 90% higher than that of the pristine polyaniline ma- trix. The synergistic effects between matrix-nano- filler were observed due to interactions between the oxygen functionalities of graphene oxide and amino groups on polyaniline and aromatic ring stackings, leading to fine dispersion and network formation. Good dispersion of graphene oxide in the conducting polymer matrix has enhanced sur- face-to-volume ratio and interfacial interactions, which contributed to overall enhanced electrical conductivity properties. Supercapacitors have been developed using conjugated polymer/graphene oxide nanocompo- sites. An important use of polymer/graphene oxide nanocomposites was observed for photovoltaics. The corrosion resistant features of the conductive polymers and graphene oxide derived nanocompo- sites have also been studied. The anticorrosion fea- tures were enhanced using conducting polymers doped on graphene oxide surfaces. In the future, new design combinations and structure-property relationships of these nanomaterials need to be in- vestigated for further developments in these fields. Moreover, research can be extended towards the development of efficient designs for microelec- tronics and digitally integrated circuits. The bio- medical sector also needs to be explored for the ap- plication of conductive polymer/graphene oxide nanocomposites. Here, synthesis processes and mechanisms need to be investigated for the for- mation of high-performance conducting nano- materials. In this review, major problems regarding con- ducting polymer/graphene oxide nanocomposites have been identified, including the benefits of com- bining graphene oxide and conducting matrices, overall property/potential advantages, and chal- lenges in this field. Graphene oxide has been iden- tified as a low-cost, efficient nanocarbon[90]. In ad- dition, lots of literature has been reported regarding the significant features and technical characteris- tics of conducting polymers and derived nanocom- posites[91,92]. The main challenges discovered for conjugated polymers include poor processability and large-scale coating development. Conse- quently, hardly any conducting polymer/graphene oxide nanomaterials have been used for commer- cial level applications. However, reports have been observed for the future market of these nanomateri- als[93]. Therefore, it is essential to investigate pre- sent research statistics and future forecasts on the upcoming industrial revolution of conducting pol- ymer/graphene oxide nanocomposite in the form of this comprehensive review article[94]. As portrayed in this article, the detailed analysis of design, ap- proaches, opportunities, and challenges has been found indispensable for the future development of conducting polymer/graphene oxide nanocompo- sites[95]. In short, this overview comprehensively cov- ered the essential aspects of conducting polymer and graphene oxide derived nanocomposites. The 8 morphology, electronic, thermal, and strength fea- tures of the nanomaterials were studied. In addition, the potential application areas for these nano- materials have been stated, like energy storage, en- ergy conversion, and anticorrosion. 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