BET surface area and density comparison for γ-Al2O3-rGO (1, 2 and 3 h calcination time) and pure γ-Al2O3 (1 h calcination time), compared with various fabrication methods .
Ceramic monoliths are applied in many insulating and high resistive engineering applications, but the energy application of ceramics monoliths is still vacant due to less conductivity of monolithic ceramics (for example, in silica- and alumina-based hybrids). This book chapter is a significant contribution in the graphene industry as it explains some novel and modified fabrication techniques for ceramics-graphene hybrids. The improved physical properties may be used to set ceramics-graphene hybrids as a standard for electrical, mechanical, thermal, and energy applications. Further, silica-rGO hybrids may be used as dielectric materials for high-temperature applications due to improved dielectric properties. The fabricated nano-assembly is important for a technological point of view, which may be further applied as electrolytes, catalysts, and conductive, electrochemically active, and dielectric materials for the high-temperature applications. In the end, this chapter discussed porous carbon as a massive source of electrochemical energy for supercapacitors and lithium-ion batteries. Carbon materials which are future of energy storage devices because of their ability to store energy in great capacity, so sustainability through smart materials got a huge potential, so hereby keeping in view all the technological aspects, this chapters sums up important contribution of graphene and porous carbon for applied applications.
- superior energy storage
- chemical activation
- lithium-ion batteries
Decades ago, scientists believed that carbon comes in two basic forms, that is, graphite and diamond, but in the last three decades, scientists have discovered new forms of carbon known as advanced carbon materials including fullerene, carbon nanotubes (CNTS), and graphene, respectively [1, 2, 3, 4, 5, 6]. In recent years, graphene is considered as an outstanding candidate for enhancing the structural, electrical, mechanical, and thermal properties of materials (for example, metals, ceramics, and polymers) [7, 8]. In hybrid nanostructures, the physical property enhancement may be possible due to excellent physical properties of the graphene. Excellent physical properties included higher thermal conductivity (5000 Wm−1 K−1), electrical conductivity (106 S m−1), and Young’s modulus (1 TPa), which are a driving force for enhancement in the physical properties of hybrids. Among the various types of graphene materials, graphite oxide-derived graphene plays an important role in increasing the physical properties of hybrids because of its surface functionalization and its ability of large-scale production at any level. Even a tiny amount of graphene in hybrids (either polymers or ceramics or metals) may alter its physical properties to a great extent. In case of graphene, the compatible structural properties and how it makes bond with various types of nanostructures are reasons for improved properties in the end product (hybrids or composites). For example, reduced graphite oxide (rGO)-polystyrene composites with a low threshold content of 0.1 (volume %) rGO have shown greatly improved electrical conductivity (approx. 0.1 S m−1); this has been possible due to good dispersion of rGO in the polymer composite matrix. Similarly, in inorganic hybrids, rGO has been used for the deposition of Co3O4 particles for increased catalytic effects, which may have been used for the decomposition of ammonium perchlorate because of the complex properties of GO and Co3O4. In another research, rGO was used to improve the mechanical properties of the bulk silicon nitride (i.e. toughness is enhanced by up to 235%), which may be used for high-performance mechanical and structural applications [8, 9]. In short, graphene being the toughest, strongest, lightweight material may act as a wonder material for future scientific revolution in every aspect of life. Even if it is combined with polymers, metals, and ceramics, it may play a significant role in improving physical properties due to its versatile surface, morphology, chemistry, and physical properties. In this chapter, we will discuss graphene combination with various ceramics and how it has been used to improve their physical properties, and porous carbon for energy storage, respectively. This book chapter will be a significant contribution to advance studies on physical properties and technological applications.
2. Highly conductive graphene-alumina-based hybrid monoliths for electrical, thermal, and mechanical applications
Low strength and brittle attributes are the main properties of ceramics. The most widely used structural ceramic is alumina, due to its good thermal conductivity and the shape stability . Alumina has a wide range of applications, some of the fields include dental implants, high speed cutting tools, chemical insulators, electrical insulators, and wear resistant coatings. Scientists have observed that mechanical properties of alumina may be improved using carbon nanotubes, for example, fracture toughness (by 94%), flexural strength (6.4%), and hardness (by 13%), respectively. On the addition of graphene platelets, about 40% enhancement in the fracture toughness of the ball milled alumina/zircon/graphene have been noticed. In another research study, the alumina-rGO core shell nanocomposites were fabricated using the method known as the sol-gel method, and it was found through this study that the BET surface area of the rGO is essential to enhance the surface charge properties of the hybrids. In another study, alumina graphene composite films were reported with a low optical gap of about 1.53 eV. Alumina-rGO nano-composites obtained via deposition during the process showed a unique morphology of aluminum nanoparticles with low prosperity and BET surface area of 242.4 m2 g−1. Moreover, scientists have found that in a microwave preparation of alumina-rGO composites, the grain size of the alumina matrix was reduced from 475 to 180 nm, which was obtained from the conventional sintering process, leading to an increase in the Young’s modulus from 148 to 180 GPa. Scientists have found that using solvothermal-hot press processing route, highly conductive alumina-rGO hybrids may be obtained, which consist of Al2O3 nanorods and rGO, respectively [7, 8, 10]. The same solvothermal method was used to form hybrids from cross-linked Al2O3 nanorods and reduced graphite oxide (rGO) platelets. Then after hot pressing, the hybrid monoliths were obtained, which were utilized for the systematical study of improved physical properties of hybrids. Using the same method, it is noticed that with the 3 h-calcinated hybrid, the Al2O3-rGO monoliths show enhanced electrical conductivity (changes from 5.1 × 10−10 to 6.7 × 101 S m−1), mechanical tensile strength (90% increase), thermal conductivity (80% increase), and a much higher dielectric constant (12 times) than the bare Al2O3. The highest values of electrical conductivity (8.2 × 101 S m−1), thermal conductivity (2.53 Wm−1 K−1), dielectric constant (104), and Young’s modulus (3.7 GPa) are determined for the alumina-rGO hybrid which is calcinated for about 1 h. It was noticed that the functional groups that contain oxygen on GO were useful for the adsorption of aluminum isopropoxide, leading to the dispersion of rGO and the Al2O3, which were obtained during the solvothermal process by the hydrolysis of the aluminum isoropoxide . The improvement in the mechanical properties was caused due to the elongated Al2O3 nanorods, which was indicated by the study of aspect ratio of the nanorods. Graphene platelets, functional groups present, and their surface properties are driving forces for enhancement in the physical properties of alumina-rGO hybrids.
2.1 Preparations of highly conductive graphene-alumina-based hybrid monoliths
In the past, alumina rGO hybrids have been prepared using sol gel, molecular level mixing, and powder coating methods, but scientists have tried some conventional preparation methods followed by high temperature treatments [7, 11]. Such methods have shown great enhancement in physical properties of hybrids. Here, we discuss one of such advanced methods, that is, the preparation of Al2O3-rGO hybrids using solvothermal-hot press processing route. Al2O3-rGO was prepared by the mixing of GO and with cyclohexane and the aluminum isopropoxide (C9H21AlO3), which was followed by the solvothermal process. The procedure involves 0.1 g of GO being first dispersed in 35 mL of cyclohexane, then 3.5 mL of aluminum isoproperoxide (C9H21AlO3) being added dropwise. The mixture is then stirred continuously at room temperature at the rate of 1000 rpm for several days until the GO powder is dispersed homogeneously but the color of the suspension changes with time. Then the products are separated by centrifugation, and the products were then washed several times with cyclohexane. The solid sample obtained are denoted as Al[O]
2.2 Improved physical properties of the highly conductive graphene-alumina based hybrid monoliths
In the case of hybrids, higher the rGO, higher will be the enhancement in the physical properties such as electrical, thermal, dielectric, and mechanical properties. In the hybrids, the surface area has been increased, and as a result, greater will be the interfacial interaction of the rGO [7, 12]. The higher rGO platelets will improve the physical properties because it provides a large surface area for interfacial interactions at nano-level. Due to higher surface area of graphene, BET surface area has been improved in the hybrids as represented in the Table 1, in comparison with various fabrication methods . Scientists believe that the higher mechanical strength is caused due to the elongated dimensions of nanorods in alumina-rGO hybrids. From the literature, it is found that 90% increase in tensile strength and 75% increase in compressive strength occur when the content of rGO is increased up to 7.707% in the hybrid. The addition of rGO affects the dielectric constant, and it increases by four orders of magnitude through a second percolation threshold [7, 8].
|Sample type||BET surface area (m2 g−1)||Bulk density (g/cm3)|
|Solvothermal-hot press processing method||γ-Al2O3 (1 h calcination time)||γ-Al2O3-rGO (3 h calcination time)||γ-Al2O3-rGO (2 h calcination time)||γ-Al2O3-rGO (1 h calcination time)||γ-Al2O3 (1 h calcination time)||γ-Al2O3-rGO (3 h calcination time)||γ-Al2O3-rGO (2 h calcination time)||γ-Al2O3-rGO (1 h calcination time)|
|Core-shell flakes Al2O3-rGO||Al2O3||Al2O3-rGO||Al2O3||Al2O3-rGO|
|In situ deposition Al2O3-rGO||Al2O3||Al2O3-rGO||Al2O3||Al2O3-rGO|
Further, the hot press processing sustains the quality of rGO in the hybrids. An increase in calcination temperature resulted in enhanced crystallinity in the Al2O3 nanorods and rGO hybrids as also shown in XRD of hybrid (Figure 1a). From the surface science point of view, this may cause enhancement in the diameters and lengths of the nanorods in the hybrid as shown in the Figure 1b. TEM images showing variations in diameters of nano-rod structures with various calcination temperatures are presented in Figure 1c–h. As a result, after calcination and hot-press processing, Al2O3-rGO monoliths were obtained with enhanced physical properties. Researchers have found that with very little rGO in the alumina hybrid, higher electrical conductivity (8.2 × 101 S m−1), higher dielectric constant by four orders of magnitude, and improved thermal conductivity (1.4 Wm−1 K−1) have been achieved . Hot pressing at 900°C ensured the complete reduction of GO and the higher crystallinity of Al2O3, resulting in enhanced physical properties. The elongated and fine Al2O3 nanorod morphology, atomic-level layered structure, and excess surface free electrons of rGO resulted in the best reported BET surface area (408 m2 g−1 in the 2 h-calcinated alumina–rGO), best thermal conductivity (2.53 Wm−1 K−1 in the 1 h-calcinated alumina—rGO), and relatively small density (0.92 g cm3 in the 1 h-calcinated alumina–rGO) and high strength (3.7 GPa in the 1 h-calcinated alumina–rGO), respectively .
Hot press processing may have an impact on the physical properties of hybrids; SEM images of hot pressed samples have shown particle-like morphology, as represented in Figure 2.
Moreover, well-aligned, elongated, and fine nanorod morphology of alumina is the reason for improvement in the mechanical strength [7, 13, 14]. Aspect ratio studies have confirmed that alumina-rGO hybrids (1 h calcinated) have more strength compared to hybrids that are calcined at more time (2 and 3 h), as shown in Figure 3.
Thus, nano-hybrids of alumina monoliths and rGO can be further applied as electrolytes, catalysts, and electrochemically active materials because of nanometer dimensions and improved physical properties [7, 15].
3. Highly conductive graphene-silica-based hybrid monoliths for dielectric applications
Improved physical properties may be achieved for -rGO monoliths using calcination followed by hot press processing. If adsorption of ethyl silicate( is required as if the group on graphene oxide contains oxygen, then it is beneficial for adsorption because it helps in uniform dispersion of rGO within the matrix, which can be obtained during the hydrothermal reaction by hydrolysis of ethyl silicate [8, 16]. If spheres in hybrids become more crystalline, then good physical properties in the hybrid can be obtained. Crystallinity in the spheres can be enhanced by increasing calcination temperature and further hot press processing at 750°C. Graphene is a material having good physical properties. As experimentally proved by scientists worldwide, the thermal, electrical, and mechanical properties of polymers, metals, and ceramics may be improved using graphene. Graphite oxide-derived graphene has tunable surface functionalization and the potential for large scale production, so it can be used to enhance the physical properties of hybrids. For the decomposition of ammonium perchlorate, can be used as a catalyst [8, 17]. To increase the catalytic effect of , rGO can be used. Basically, rGO helps in uniform deposition of in inorganic hybrids. Silica has good functionalized ability and is very stable, so it can be used as an additive in numerous applications. In biomedical, polymer, and ceramics engineering, silica is used for various purposes. rGO can be used to enhance the physical properties of silica. Epoxy--rGO hybrids have enhanced thermal conductivity (0.452 W), storage modulus (3.56), and dielectric constant (77.23). In another study, rGO has been used to improve the gas sensing performance, which was obtained by an electrostatic self- assembly approach. If dispersion, corrosion resistance, and barrier properties of hybrids are required to be enhanced, then the presence of rGO is essential, and this was found when nanocomposites of silica-graphene oxide were fabricated using in situ gel method. -graphene hybrids are better gas sensors as compared to rGO-based sensors [18, 19]. Toward 50 ppm for 850 s, the gas sensing response of rGO-based sensors is 1.5% and that of -graphene-based sensors is 31.5%, respectively. It has been shown that -rGO composites having enhanced BET surface area (676 ) can be obtained by one-step hydrothermal method. On addition of ultrathin graphene, -polyvinyldiene fluoride having high dielectric constant (72.94) and low dielectric loss (0.059) is obtained. Composites of epoxy-silica-graphene oxide have enhanced tensile strength, which leads to an increase in fracture toughness and Young’s modulus . The physical properties of -rGO such as dielectric, electrical, mechanical, and thermal properties need to be improved further. So, in this chapter, we are discussing various physical properties of silica-rGO hybrids for dielectric applications.
3.1 Preparation of highly conductive graphene-silica based hybrid monoliths for dielectric applications
In brief preparation using solvothermal-hot press processing route , GO is mixed with cylcohexane and ethylsilicate (, followed by hydrothermal reaction to form -rGO hybrids. For the preparation, 0.1 g of GO is dispersed in 50 mL cyclohexane, followed by addition of 5 mL of ethylsilicate dropwise. Then GO powder is homogeneously dispersed by stirring the mixture at the speed of 1500 rpm for several days at room temperature. The products are then separated by using centrifugation. The products are then washed with cyclohexane for several times. The obtained solid samples are represented as /GO. From suspension of 0.1, 0.2 and 0.3 g GO, /GO powders were obtained, respectively. The solid samples obtained are then dispersed in 75 mL cyclohexane, and then for hydrothermal reaction, the mixture is transferred to a 100 mL Teflon-lined stainless-steel autoclave. The reaction is then carried out at 420 K for 4 h, and the sample obtained is then centrifuged and dried at 303 K. The sample obtained is denoted as -rGO. Then calcination of -rGO is carried out at 800 K for 1 h. To study the physical properties, using the same method, hybrids of -rGO consisting of 1.55, 6.75, and 10.82 wt% rGO are obtained. 1.55, 6.75, and 10.82% rGO is referred to as sample-a, sample-b, and sample-c, respectively. Without adding GO by using the same procedure, pure (referred to as sample-d) is obtained. The calcination temperature is then set as 500, 600, 700, and 800 K for a processing time of 1 h to study the effect of calcination temperature on crystallinity.
3.2 Surface and physical properties of highly conductive graphene-silica-based hybrid monoliths for dielectric applications
Researchers have developed a hydrothermal-hot press processing technique, a simple and efficient method that can improve the thermal, electrical, dielectric, and mechanical properties of the hybrid [8, 20]. By a hydrothermal reaction, GO is dispersed in cyclohexane and ethylsilicate to produce hybrids composed of rGO and silica monoliths [20, 21]. The SEM morphology of hybrids has shown sphere-particle-like morphology with thin layers of rGO, which act as a support for elongated matrix, as shown in Figure 4.
SEM images of SiO2-rGO-1.55% (sample a) at various temperatures are shown in Figure 5. At all temperatures, hybrids have shown sphere-like morphology, but sphere size changes at various temperatures [9, 22].
The solvothermal-hot press processing method shows the best reported electrical conductivity (0.143 ), thermal conductivity (1.612 W), and higher dielectric constants for -rGO monoliths. Thus, due to enhanced physical properties of the nano hybrids, it can be applied as electrolytes, catalysts, conductive and electrochemically active materials, and dielectrics for high-temperature applications [8, 12, 23].
Table 2 have shown BET surface area and mesoporous volume % analysis for the hybrids. From the table, it is confirmed that BET surface area has been increased with more rGO in the hybrids, while mesoporous volume % increased with more silica [8, 24].
|Sample type||BET surface area (m2 g−1)||Total volume (cm3 g−1)||Mesoporous volume (cm3 g−1)||Microporous volume (cm3 g−1)||Mesoporous volume (%)|
The dielectric properties of the SiO2-rGO hybrids and bare SiO2 were measured using an LCR meter as shown in Figure 6. The dielectric properties of the hybrids were measured at a frequency of 1 kHz. For SiO2, its dielectric constant is found to be around 3.79, which is closer to that of pure silica. For sample a, the dielectric constant significantly increased by a value of 497, which indicates the presence and proximity of a first percolation threshold.
The enhanced dielectric constant (up to order of 105 and 107) was determined for samples b and c, which is much higher compared to that for sample d. Formation of conductive pathways is one of the main reasons for an increase in the overall dielectric constants. In sample c, significant leakage current leads to higher dielectric loss (300). By further increasing the rGO, the dielectric constant increased by seven orders of magnitude, indicating the presence of a second percolation threshold, which is achieved through the higher value of dielectric constant. Similarly, the dielectric loss indicates very similar behavior in the real part of the dielectric constant as shown in the inset of Figure 6. Scientists have experimentally proved that a small amount of rGO in hybrids can enhance dielectric properties to a great extent. The existence of a double percolation threshold in SiO2 and the rGO hybrids can be significant for applied applications because it can be used to enhance the dielectric permittivity (up to 107) with the addition of a small percentage of rGO in the hybrids. Silica-rGO hybrids may be used as dielectric materials for high-temperature applications due to better dielectric properties [7, 8, 23, 25].
4. Porous carbon for superior energy storage
A process called one-step carbonization-activation which is used to transform frozen tofu, mainly a source of carbon (C) and nitrogen (N), into a co-doped porous carbon having N (0.6–6.7 wt%) and O (3.6–9.5 wt %) and bearing a specific area of about 3134 m2 g−1. Mesopores and micropores constitute a high volume of this hierarchy carbon, i.e. 1.11 cm3 g−1 consists of mesopores and 0.71 cm3 g−1 of micropores with a regular pore size appropriation somewhere in the range of 0.8–4 nm [9, 26]. When used as electrodes in supercapacitors, this porous carbon shows a specific capacitance of 243 F g−1 with sulfuric acid used as electrolyte and retains 93% of its initial capacitance after 10,000 cycles. In 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), a specific resistance of 170 F g−1 and a reliable rate capability can be observed using above prepared carbon which also provides an energy density of 72 W h kg−1 (calculated at an average power density of 889 W kg−1). A total of 25 light emitting diodes (LEDs) which are connected in parallel fashion may be empowered immediately for more than 2 min in the wake of being charged for 25 s, using supercapacitors comprising of porous carbon, at a current density of 10 A g−1. What’s more, the porous carbon displays a high reversible charge capacity of 2120 mA h g−1 in the first cycle (estimated at 0.1 A g−1) or 1035 mA h g−1 after 300 cycles (estimated at 1 A g−1), when used as an anode for Li-ion batteries [9, 26, 27].
4.1 Preparation of porous carbon for superior energy storage
Devices having energy due to chemical reactions are getting more fame than other energy storage devices due to their considerable potential applications . An instantaneous charging and discharging capability, which leads toward an efficient power density of about 10 kW kg−1, can be observed in supercapacitors. The fabrication flowchart for porous carbon is shown in Figure 7.
4.2 Surface and physical properties of porous carbon for superior energy storage
On the other hand, in spite of having longer charging time, a high energy density of about 100–200 W h kg−1 can be referred in lithium-ion batteries (LIBs). There are two fundamental processes by which the energy can be stored in supercapacitors, which are as follows: (i) pseudocapacitive electrodes store ions based on quick faradaic reactions at the electrode-electrolyte interface, and (ii) electrical double-layer capacitive electrodes store energy by the adsorption and desorption of ions on the large surface area of the porous material [29, 30]. The working of lithium-ion batteries depends upon the transfer of lithium ions in between the cathode and the anode. The mechanism by which the lithium ions are stored or released, in lithium-ion batteries, depends upon the nature of the material of which the electrode is made . High electrical conductivity, tailored porosity, and chemical stability are the main features of carbon materials that make their extensive use in many devices such as commercial supercapacitors and lithium-ion batteries (LIBs) . Scientists reveal that in supercapacitors, mesopores and micropores are the main constituents of porous carbon as they provide ion buffering reservoirs, movement of ions and then storage site for ions, respectively. In lithium-ion batteries, the reversible Li-ion storage capacity is retained to an approximation of 372 mA h g−1, for graphite, using graphite anode in lithium-ion batteries which interacts with Li-ions to produce a compound, LiC6, that retains the reversible storage capacity to its mention value. In addition, because of the permeable structure, the use of carbon materials as a framework of electrodes, that is, in lithium-ion batteries and other energy storage devices, is increasing nowadays . It is believed that the supercapacitors cannot fulfill the energy requirements of future electrical devices because of their low energy density (less than 6 W h kg−1). Also, the capacity and rate capability of electrodes in LIBs are below to standards. To approach the above-mentioned requirements, porous carbon having good electrical conductivity and a modified 3-dimensional structure is required .
In the recent decades, a number of techniques named activation, self-assembly, and templating have been used for the production of porous carbon materials. But activation exceeds other techniques owing to the fact that it tends to produce a carbon of a large specific surface area of about 200 m2 g−1 and other useful properties. Activation can also play an important role in the production of novel carbon by doing a proper processing of nanostructured carbon precursors . For instance, graphene platelets can be rebuilt thoroughly to a 3D porous carbon having a specific surface area of approximately 3100 m2 g−1 and pore size appropriation somewhere in between 0.6 and 5 nm, during the activation of microwave-exfoliated graphite oxide in the presence of KOH. Moreover, in graphite grids, the n-type can be brought up using the atoms like nitrogen which has the ability to donate electrons. The carbon doped with nitrogen finds its applications as anode in lithium-ion batteries because the hybridization between the lone pair electrons of nitrogen with π electrons of carbon can assist lithium lodging [36, 37]. Porous carbon materials derived from biomass are more sustainable than derived from other materials like coal, pitch, polymers, etc. Scientists have indicated that porous carbons for energy stockpiling applications can be acquired from different biomass sources, for example, rice husks, rice straw, algae, what’s more, water bamboo. For instance, lithium and other confrere elements experience a one-step pyrolysis-activation synthesis to transform willow catkin into a cross-linked layered porous carbon which is co-doped with two metals, that is, nitrogen (N) and sulfur (S). The carbon thus produced exhibits some outstanding features related to chemical performance like it shows a specific capacitance of 298 F g−1 at 0.5 A g−1 in 1 molar solution of Na2SO4 with the great cycling stability along with the capacitance loss of only 2% when checked after 10,000 cycles at 5 A g−1.
Tofu, rich in moisture, proteins, sugars, and follow sums of minerals, is a bounteous asset and has been viewed as a characteristic source of carbon and nitrogen [9, 36, 38]. It is obvious from the above discussion that tofu is a favorable predecessor material in the manufacture of carbon materials used for energy storage devices, but further developments are required for better performance like enhanced capacitance in symmetric supercapacitors and rate capability/cyclic stability in lithium-ion batteries. The features like large surface area, hierarchical (permeable) porous structure, and heteroatomic doping make the use of porous carbon samples (obtained from tofu) suitable for the material used as an anode in Li-ion batteries [9, 35, 38].
This study presented some novel and modified fabrication techniques for ceramics-graphene hybrids. The improved physical properties may be used to set ceramics-graphene hybrids as a standard for electrical, mechanical, thermal, and energy applications. Further, silica-rGO hybrids may be used as dielectric materials for high temperature applications due to improved dielectric properties. The fabricated nano-assembly is important for a technological point of view, which may be further applied as electrolytes, catalysts, and conductive, electrochemically active, and dielectric materials for the high-temperature applications. In addition, the porous carbon as a massive source of electrochemical energy for supercapacitors and lithium-ion batteries is also addressed.
Conflict of interest
The authors have declared no ‘conflict of interest’.
Novoselov KS, Fal’Ko VI, Colombo L, Gellert PR, Schwab MG, Kim K. A road map for graphene. Nature. 2012; 490:192-200
Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, et al. Electric field effect in atomically thin carbon films. Science. 2004; 306:666-669
Pham VP, Jang H-S, Whang D, Choi J-Y. Direct growth of graphene on rigid and flexible substrates: Progress, applications, and challenges. Chemical Society Reviews. 2017; 46:6276-6300
Pham PV. The new etching technologies of graphene surfaces. ACS Omega. 2018; 3:8036-8041
Pham VP, Nguyen MT, Park JW, Kwak SS, Nguyen DHT, Mun MK, et al. Chlorine-trapped CVD bilayer graphene for resistive pressure sensor with high detection limit and high sensitivity. 2D Materials. 2017; 2:4
Pham VP, Jo YW, Oh JS, Kim SM, Jhon MS, Yeom GY. Effect of plasma–nitric acid treatment on the electrical conductivity of flexible transparent conductive films. Japanese Journal of Applied Physics. 2013; 52:7R
Ikram M, Tao Z, Ye J, Qayyum HA, Sun X, Xu J. Enhanced physical properties of γ-Al2O3–rGO hybrids prepared by solvothermal and hot-press processing. RSC Advances. 2018; 8:8329-8337
Ikram M, Qayyum HA, Ali S, Tan Z, Ahmad M, Xu J. Hydrothermal-hot press processed SiO2-rGO hybrid with enhanced physical properties. Journal of Solid State Chemistry. 2018; 265C:364-371
Sun X, Ye J, Pan F, Xu J, Cheng T, Wang X, et al. Hierarchical porous carbon obtained from frozen tofu for efficient energy storage. New Journal of Chemistry. 2018; 42:12421-12428
Balazs AC, Emrick T, Russell TP. Nanoparticle polymer composites: Where two small worlds meet. Science. 2006; 314:1107-1110
Yang X, Zhang X, Ma Y, Huang Y, Wang Y, Chen Y. Superparamagnetic graphene oxide–Fe3O4 nanoparticles hybrid for controlled targeted drug carriers. Journal of Materials Chemistry. 2009; 19:2710-2714
Stankovich S, Dikin DA, Dommett GHB, Kohlhaas KM, Zimney EJ, Stach EA, et al. Graphene-based composite materials. Nature. 2006; 442:282-286
Zhang Z, Pinnavaia TJ. Mesostructured γ-Al2O3 with a Lathlike framework morphology. Journal of the American Chemical Society. 2002; 124:12294-12301
Ahmad I, Cao H, Chen H, Zhao H, Kennedy A, Zhu YQ. Carbon nanotube toughened aluminium oxide nanocomposite. Journal of the European Ceramic Society. 2010; 30:865-873
Jagminas A, Kaciulis S, Klimas V, R’eza A, Mickevicius S, Soltani P. Fabrication of graphene-alumina heterostructured films with nanotube morphology. Journal of Physical Chemistry C. 2016; 120:9490-9497
Benavente R, Pruna A, Borrell A, Salvador MD, Pullini D, Penaranda-Foix F, et al. Fast route to obtain Al2O3-based nanocomposites employing graphene oxide: Synthesis and sintering. Materials Research Bulletin. 2015; 64:245-251
Liu Y, Ma D, Han X, Bao X, Frandsen W, Wang D, et al. Hydrothermal synthesis of microscale boehmite and gamma nanoleaves aluminia. Materials Letters. 2008; 62:1297-1301
Chen YF, Lee CY, Yeng MY, Chiu HT. The effect of calcination temperature on the crystallinity of TiO2 nanopowders. Journal of Crystal Growth. 2003; 247:363-370
Zhang Y, Li D, Tan X, Zhang B, Ruan X, Liu H, et al. High quality graphene sheets from graphene oxide by hot-pressing. Carbon. 2013; 54:143-148
Liu H, Choy KL, Roe M. Enhanced conductivity of reduced graphene oxide decorated with aluminium oxide nanoparticles by oxygen annealing. Nanoscale. 2013; 5:5725-5731
Wang SX, Zou KX, Qian YX, Deng YF, Zhang L, Chen G.H. et al. Insight to the synergistic effect of N-doping level and pore structure on improving the electrochemical performance of sulfur/N-doped porous carbon cathode for Li-S batteries. Carbon 2019; 144:745-755
Nan CW, Shen Y, Ma J. Physical properties of composites near percolation. Annual Review of Materials Research. 2010; 40:131-151
Kim JY, Lee WH, Suk JW, Potts JR, Chou H, Kholmanov IN, et al. Chlorination of reduced graphene oxide enhances the dielectric constant of reduced graphene oxide/polymer composites. Advanced Materials. 2013; 25:2308-2313
Zaretsky EB. High temperature impact response of 998 alumina. Journal of Applied Physics. 2013; 114:183518
Yoo E, Kim J, Hosono E, Zhou H-s, Kudo T, Honma I. Large Reversible Li Storage of Graphene Nanosheet Families for Use in Rechargeable Lithium Ion Batteries. Nano Letters. 2008; 8:2277-2282
Wang L, Zhang G, Zhang X, Shi H, Zeng W, Zhang H, et al. Porous ultrathin carbon nanobubbles formed carbon nanofiber webs for high-performance flexible supercapacitors. Journal of Materials Chemistry A. 2017; 5:14801-14810
Kang K, Meng YS, Br ́eger J, Grey CP, Ceder G. Electrodes with high power and high capacity for rechargeable lithium batteries. Science. 2006; 311:977-980
Staaf L, Lundgren P, Enoksson P. Present and future supercapacitor carbon electrode materials for improved energy storage used in intelligent wireless sensor systems. Nano Energy. 2014; 9:128-141
Wang B, Zhang W, Wang L, Wei J, Bai X, Liu J, et al. Three dimensional carbon-bubble foams with hierarchical pores for ultra-long cycling life supercapacitors. Nanotechnology. 2018; 29:275706
Shopsowitz KE, Hamad WY, MacLachlan MJ. Chiral nematic mesoporous carbon derived from nanocrystalline cellulose. Angewandte Chemie, International Edition. 2011; 50:10991-10995
Zhu Y, Murali S, Stoller MD, Ganesh K, Cai W, Ferreira PJ, et al. Carbon-based supercapacitors produced by activation of graphene. Science. 2011; 332:1537-1541
Sankar S, Lee H, Jung H, Kim A, Ahmed ATA, Inamdar AI, et al. Ultrathin graphene nanosheets derived from rice husks for sustainable supercapacitor electrodes. New Journal of Chemistry. 2017; 41:13792-13797
Sevilla M, Fuertes AB. Hierarchical microporous/mesoporous carbon nanosheets for high-performance supercapacitors. ACS Nano. 2014; 8:5069-5078
Sing KS. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure and Applied Chemistry. 1985; 57:603-619
Zhou Q, Chang J, Jiang Y, Wei T, Sheng L, Fan Z. Fast charge rate supercapacitors based on nitrogen-doped aligned carbon nanosheet networks. Electrochimica Acta. 2017; 251:91-98
Yang G, Niu J, Shao R, Liang J, Dou M, Li Z, et al. A facile molecularly engineered copper (II) phthalocyanine as hole transport material for planar perovskite solar cells with enhanced performance and stability. Nano Energy. 2017; 36:322-330
Fang Y, Lv Y, Che R, Wu H, Zhang X, Gu D, et al. Two-dimensional mesoporous carbon nanosheets and their derived graphene nanosheets: Synthesis and efficient lithium ion storage. Journal of the American Chemical Society. 2013; 135:1524-1530
Hou J, Cao C, Idrees F, Ma X. Hierarchical porous nitrogen-doped carbon nanosheets derived from silk for ultrahigh-capacity battery anodes and supercapacitors. ACS Nano. 2015; 9:2556-2564