Chemically-reduced Graphene Research Articles

Machine learning assisted electrochemical sensing technology for the detection of nitrate ions in PM2.5

This study investigates a graphene-modified glassy carbon electrode for detecting nitrate ions in particulate matter (PM2.5). The electrode configuration consists of a glassy carbon base electrode drop-coated with chemically-reduced graphene (CRGN), followed by an optimized nitrate ion-selective membrane (NO3-ISM) layer. Electrochemical impedance spectroscopy demonstrates graphene’s ability to enhance electron transfer by mitigating water layer formation. The nitrate sensor exhibits a linear potentiometric response from 0.1 mM to 0.1 M nitrate and theoretical Nernstian sensitivity. However, chloride interferences are observed. To improve selectivity, a support vector machine model utilizing particle swarm optimization (PSO-SVM) is developed. This machine learning approach shows significantly higher predictive accuracy than univariate calibration, even in mixed nitrate-chloride samples. The combination of the graphene-modified sensor and PSO-SVM algorithm provides an optimized nitrate detection strategy, advancing technologies for air quality monitoring.

A novel electrochemical sensing platform based on mono-dispersed gold nanorods modified graphene for the sensitive determination of topotecan

In this research, we developed a novel design to fabricate a sensitive and selective electrochemical sensor based on high-quality graphene decorated with mono-dispersed gold nanorods (AuNRDs) for the determination of topotecan (TPC) in human blood serum. For this purpose, the screen-printed electrode (SPE) was firstly modified with graphene prepared by metal intercalation process (MI-GR), and then followed by the decoration of mono-dispersed AuNRDs synthesized by seed mediated growth method. The synthesized MI-GR and AuNRDs samples were characterized by Raman, XPS, UV-Vis and TEM techniques. Electrochemical studies indicated that the electrocatalytic activity of MI-GR has superior than that of chemically reduced graphene (CR-GR) prepared by conventional approach due to its faster electron transfer ability. Moreover, AuNRDs/MI-GR modified SPE (AuNRDs/MI-GR/SPE) demonstrated a wide linearity in the range of 0.1 – 16.0 μM with a low detection limit of 22.0 nM. The analytical reliability of AuNRDs/MI-GR/SPE was successfully confirmed by the detection of TPC in human blood serum with the satisfactory recoveries at the range of 99.8–100.07%. AuNRDs/MI-GR/SPE could be utilized as an alternative analytical tool for the determination of anti-cancer agents such as TPC in the next generation clinical applications.

Chemically-reduced graphene reinforced polyetherimide nanocomposites: dielectric behavior, thermal stability and mechanical properties

Recently, the research on improvement of dielectric and mechanical performances of the high-performance polymers like polyether imide (PEI) by reinforcement of modified graphene nanosheets has received enormous attention in both defence and commercial sectors. Reduced graphene oxide (rGO) reinforced PEI nanocomposites were fabricated by dispersion of rGO nanosheets in the polyamic acid (PAA) followed by in situ partial thermal reduction and imidization of the as-prepared PAA/rGO nanocomposites. Chemically synthesized graphene oxide was reduced with hydrazine hydrate. Compared to pure PEI, the dielectric permittivity of the PEI nanocomposite with 5 wt% rGO revealed remarkable increase by about 132 times, which is attributed to the enhanced interfacial polarization (Maxwell-Wagner-Sillars effect) at the rGO-PEI interfaces. The PEI nanocomposite exhibited noticeably low dielectric loss (0.43 at 1 kHz) even at high rGO content (5 wt%) due to the low current leakage. The maximum dielectric performance of the nanocomposites was observed near percolation threshold (≈1.12 vol%). Upon thermal annealing, both AC conductivity and dielectric permittivity (<10 kHz) of the nanocomposites were substantially decreased. With incorporation of rGO nanosheets, the mechanical properties of the nanocomposite films were remarkably increased with maximum tensile strength of 423 MPa and Young’s modulus of 2.93 GPa at 5 wt% rGO loading, suggesting excellent stress transfer between PEI-matrix and rGO nanosheets. The PEI/rGO nanocomposites exhibited significant improvement in thermal stability with high char yield (> 40%) in N2 atmosphere compared to pure PEI.

A comparative investigation of aminosilane/ethylene diamine–functionalized graphene epoxy nanocomposites with commercial and chemically reduced graphene: static and dynamic mechanical properties

Incorporation of nanosized fillers into polymers has created new composites by expanding the functions and applications while retaining the excellent engineering and processing flexibility inherent to polymers. Compared with traditional nanofillers, more recently, graphene has been increasingly preferred as a candidate for strengthening and/or functionalizing polymer nanocomposites. The easy synthetic methods, low cost, and non-toxicity of graphene make this material attractive for many technological applications. Herein, we discuss the synthesis of different types of graphene from graphite via graphene oxide reduction. Commercial graphene (CG) as well as the synthesized chemically reduced graphene (CRG) and chemically reduced silane-modified graphene (SMG) were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. The results confirmed that the silane molecules were attached on the surface of graphene sheets. Simultaneously, most of residual oxygen-containing functional groups of GO were reduced and the sp2-hybridized structure of graphene was restored. The utilization of these graphene-based materials in the fabrication of epoxy nanocomposites with enhanced properties has been explored and compared with those of neat epoxy and CG/epoxy nanocomposites. Inclusion of 0.25 phr CRG and SMG in an epoxy resin showed 28% and 32% increases in tensile strength, and the corresponding fracture toughness displayed 67.6% and 66.3% increase respectively. The improved mechanical properties of SMG/epoxy nanocomposites might be due to the uniform dispersion of functionalized graphene and strong interfacial bonding between modified graphene and epoxy resin.

Adsorption and desorption of phenanthrene by magnetic graphene nanomaterials from water: Roles of pH, heavy metal ions and natural organic matter

The adsorption of phenanthrene onto magnetic graphene oxide (MGO), magnetic chemically-reduced graphene (MCRG) and magnetic annealing-reduced graphene (MARG) were compared to examine their unique adsorption properties. The effects of environmental factors on the adsorption-desorption properties of phenanthrene e.g. pH, heavy metal ions, and natural organic matter were also investigated. MCRG had the highest adsorption capacity for phenanthrene, mainly due to the larger surface area and pore volume, and numerous wrinkles of MCRG. The π–π interaction was the predominant adsorption mechanism of MCRG. Coexisting Cd(II) and As(V) had a minor impact on phenanthrene adsorption by MCRG, while the adsorption capacity of phenanthrene decreased considerably with coexisting humic acids. Phenanthrene caused desorption hysteresis, which was largely suppressed by humic acids. The desorption hysteresis was ascribed to the entrapment of phenanthrene molecules derived from the generation of closed interstitial spaces caused by the rearrangement of graphene nanosheets onto MCRG. Steric hindrance was much larger with adsorbed humic acid molecules. Our findings on magnetic graphene nanomaterials (MGNs) and related adsorption-desorption properties highlight their potential applications as efficient adsorbents and their possible risks in natural aquatic environments.

Selective removal of diethanolamine from methyldiethanolamine solution using chemically reduced single-layer graphene and activated carbon

ABSTRACTThe adsorption capacity of chemically reduced graphene (CRG) in selective removal of diethanolamine (DEA) from a mixture of methyldiethanolamine (MDEA) in aqueous solutions was evaluated and compared with commercially available activated carbons using batch studies. Four equilibrium isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin–Radushkevish and three different kinetics models such as Pseudo-first order, Pseudo-second order and Intra-particle diffusion were applied. The maximum uptake capacity for DEA using CRG at 296 K (250.0 mg/g) was high compared to two selected activated carbons (1.05 and 0.559 mg/g). The adsorption of DEA was found to be spontaneous and endothermic process with all the adsorbents.

Innovations in polymer nanocomposite coatings for EMI Shielding applications

Start Excessive usage of electronic gadgets, telecommunication devices and electrical appliances has led to unwanted electromagnetic interference (EMI) as side effect. The EMI pollution interferes with the performance and functioning of the electrical equipments, which is generated through the conduction or radiation of emitted electromagnetic (EM) waves. In addition to affecting the quality of electrical appliances, EMI has a huge negative impact on the health and life of living organisms. Moreover, microwave frequency operated functions such as radar surveillance systems; weather radar, military aviation, radar guns, wireless technology and satellite communication are more prone to EMI pollution and specifically with regard to stealth purposes. In this paper carbon nanomaterial based polyurethane nanocomposites have been synthesized and investigated for decreasing the EM wave pollution due to their light weight, flexibility, optimum conductivity and good dielectric properties. Three different types of graphene sheets such as thermally reduced and exfoliated graphene (TRG); chemically reduced graphene (CRG) and Polyvinyl-pyyrolidone stabilized silver nanoparticles based graphene nanohybrid (Ag-PVP-CRG) have been synthesized and characterized for EMI shielding properties. Further, TRG, CRG and Ag-PVP- CRG sheets have been dispersed in thermoplastic polyurethane (TPU) polymeric matrix to create multifunctional nanocomposite films with properties such as EMI shielding, electrically conductivity and dielectric behavior. The study presents for the first time a comparative evaluation of three different types of graphene sheets in both neat and nanocomposite form. The synthesis of Ag-PVP-CRG nanohybrids and its application for EMI shielding is novel and reported for the first time for such an application.

Novel insight into adsorption and co-adsorption of heavy metal ions and an organic pollutant by magnetic graphene nanomaterials in water

The adsorption of tetracycline (TC), cadmium [Cd(II)] and arsenate [As(V)] onto magnetic graphene oxide (MGO), magnetic chemically-reduced graphene (MCRG) and magnetic annealing-reduced graphene (MARG) was investigated to understand the adsorption properties and molecular mechanisms. The adsorption of three contaminants was pH-dependent and the adsorption capability followed the order of MGO > MCRG > MARG, and hence MGO was selected to systematically study the adsorption behaviors in three different types of binary systems. The maximum adsorption capacities of MGO were 252 mg/g for TC, 234 mg/g for Cd(II) and 14 mg/g for As(V). The superiority of MGO was mainly attributed to its high dispersibility, thin nanosheets and various O-containing functional groups. In addition to H-bonding and π–π interactions, the strong adsorption of TC onto MGO was mainly due to the n–π electron-donor–acceptor (EDA) effect, with the maximum adsorption around pKa of TC. The mutual effects of TC and Cd(II) in the simultaneously added system were negligible. Adsorption of As(V) was significantly suppressed in the presence of TC, whilst As(V) hardly affected TC adsorption. The adsorptions of Cd(II) and As(V) in the co-adsorption system were increased by 65% and 30%, respectively. This synergistic effect resulted from the electrostatic attraction and the formation of type A ternary surface complexation. These new insights were valuable for elucidating the interaction mechanisms and designing novel adsorbents for traditional and emerging pollutions in practical application.

Graphene Oxide/ZnS:Mn Nanocomposite Functionalized with Folic Acid as a Nontoxic and Effective Theranostic Platform for Breast Cancer Treatment.

Nanoparticle-based cancer theranostic agents generally suffer of poor dispersability in biological media, re-agglomeration over time, and toxicity concerns. To address these challenges, we developed a nanocomposite consisting of chemically-reduced graphene oxide combined with manganese-doped zinc sulfide quantum dots and functionalized with folic acid (FA-rGO/ZnS:Mn). We studied the dispersion stability, Doxorubicin (DOX) loading and release efficiency, target specificity, internalization, and biocompatibility of FA-rGO/ZnS:Mn against folate-rich breast cancer cells, and compared to its uncoated counterpart (rGO/ZnS:Mn). The results indicate that DOX is adsorbed on the graphene surface via π–π stacking and hydrophobic interaction, with enhanced loading (~35%) and entrapment (~60%) efficiency that are associated to the chelation of DOX and surface Zn2+ ions. DOX release is favored under acidic conditions reaching a release of up to 95% after 70 h. Membrane integrity of the cells assessed by Lactate dehydrogenase (LDH) release indicate that the surface passivation caused by folic acid (FA) functionalization decreases the strong hydrophobic interaction between the cell membrane wall and the edges/corners of graphene flakes. Chemotherapeutic effect assays reveal that the cancer cell viability was reduced up to ~50% at 3 µg/mL of DOX-FA-rGO/ZnS:Mn exposure, which is more pronounced than those obtained for free DOX at the same doses. Moreover, DOX-rGO/ZnS:Mn did not show any signs of toxicity. An opposite trend was observed for cells that do not overexpress the folate receptors, indicating that FA functionalization endows rGO/ZnS:Mn with an effective ability to discriminate positive folate receptor cancerous cells, enhancing its drug loading/release efficiency as a compact drug delivery system (DDS). This study paves the way for the potential use of functionalized rGO/ZnS:Mn nanocomposite as a platform for targeted cancer treatment.

Effects of Graphene Oxide and Chemically-Reduced Graphene Oxide on the Dynamic Mechanical Properties of Epoxy Amine Composites.

Composites based on epoxy/graphene oxide (GO) and epoxy/reduced graphene oxide (rGO) were investigated for thermal-mechanical performance focusing on the effects of the chemical groups present on nanoadditive-enhanced surfaces. GO and rGO obtained in the present study have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) demonstrating that materials with different oxidation degrees have been obtained. Thereafter, GO/epoxy and rGO/epoxy nanocomposites were successfully prepared and thoroughly characterized by dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM). A significant increase in the glass transition temperature was found in comparison with the neat epoxy. The presence of functional groups on the graphene surface leads to chemical interactions between these functional groups on GO and rGO surfaces with the epoxy, contributing to the possible formation of covalent bonds between GO and rGO with the matrix. The presence of oxidation groups on GO also contributes to an improved exfoliation, intercalation, and distribution of the GO sheets in the composites with respect to the rGO based composites.

Pyrolytic-carbon coating in carbon nanotube foams for better performance in supercapacitors

Abstract Nowadays, the wide-spread adoption of supercapacitors has been hindered by their inferior energy density to that of batteries. Here we report the use of our pyrolytic-carbon-coated carbon nanotube foams as lightweight, compressible, porous, and highly conductive current collectors in supercapacitors, which are infiltrated with chemically-reduced graphene oxide and later compressed via mechanical and capillary forces to generate the active electrodes. The pyrolytic carbon coatings, introduced by chemical vapor infiltration, wrap around the CNT junctions and increase the surface roughness. When active materials are infiltrated, the pyrolytic-carbon coatings help prevent the π-stacking, enlarge the accessible surface area, and increase the electrical conductivity of the scaffold. Our best-performing device offers 48% and 57% higher gravimetric energy and power density, 14% and 23% higher volumetric energy and power density, respectively, and two times higher knee frequency, than the device with commercial current collectors, while the “ true-performance metrics” are strictly followed in our measurements. We have further clarified the solution resistance, charge transfer resistance/capacitance, double-layer capacitance, and Warburg resistance in our system via comprehensive impedance analysis, which will shed light on the design and optimization of similar systems.

Overview of supercapacitance performance of graphene supported on porous substrates

Graphene has attracted great attention for supercapacitor electrode materials owing to unique electrochemical properties. The electrochemical capacitance of graphene supercapacitor is highly in dependence on the substrate and graphene. This overview mainly focuses on the preparation and electrochemical capacitance of the electroactive graphene supported on porous substrate of microporous nickel foam and nanoporous titanium nitride. The graphene includes the chemical-reduced graphene oxide, hydrothermal-reduced graphene oxide and thermal-reduced graphene oxide. The porous supporting substrates include micro-structured porous nickel foam and nano-structured titanium nitride nanotube array. The supercapacitance performance of porous graphene electrode materials has been fully summarised involving chemical-reduced graphene oxide/nickel foam, hydrothermal-reduced graphene oxide/nickel foam, chemical-reduced graphene oxide/titanium nitride and thermal-reduced graphene oxide/titanium nitride. The porous substrate structure of nickel foam and titanium nitride along with the graphene reduction degree could coordinately influence the supercapacitance performance.

ZnO-nanorods/graphene heterostructure: a direct electron transfer glucose biosensor.

ZnO-nanorods/graphene heterostructure was synthesized by hydrothermal growth of ZnO nanorods on chemically reduced graphene (CRG) film. The hybrid structure was demonstrated as a biosensor, where direct electron transfer between glucose oxidase (GOD) and electrode was observed. The charge transfer was attributed to the ZnO nanorod wiring between the redox center of GOD and electrode, and the ZnO/graphene heterostructure facilitated the transport of electrons on the hybride electrode. The glucose sensor based on the GOD-ZnO/CRG/Pt electrode had a high sensitivity of 17.64 μA mM−1, which is higher than most of the previously reported values for direct electron transfer based glucose biosensors. Moreover, this biosensor is linearly proportional to the concentration of glucose in the range of 0.2–1.6 mM. The study revealed that the band structure of electrode could affect the detection of direct electron transfer of GOD, which would be helpful for the design of the biosensor electrodes in the future.

Nonisothermal and isothermal crystallization behavior of isotactic polypropylene/chemically reduced graphene nanocomposites

Graphene oxide was firstly prepared by a modified Hummers method and then reduced via hydrazine reduction method to obtain chemically reduced graphene (CRG). The morphology of CRG dispersed in the isotactic polypropylene (iPP) matrix was observed using transmission electron microscope and rheological measurement methods. Nonisothermal and isothermal crystallization behaviors of iPP/CRG nanocomposites were investigated by differential scanning calorimetry and polarizing optical microscopy methods, respectively. Nonisothermal crystallization measurement revealed that CRG elevated the crystallization temperature of iPP due to the nucleating effect of CRG. And during isothermal crystallization process, the half time crystallization of nanocomposites was significantly reduced. Furthermore, the images of polarized optical microscopy also exhibited that the nucleation density of nanocomposites was much higher than that of neat iPP due to the heterogeneous nucleation of CRG even at a loading of 0.5%. POLYM. COMPOS., 38:E342–E350, 2017. © 2016 Society of Plastics Engineers

Adsorption and coadsorption of organic pollutants and a heavy metal by graphene oxide and reduced graphene materials

The adsorption and coadsorption of naphthalene, 1-naphthol and Cd2+ onto graphene oxide (GO), chemically reduced graphene (CRG) and annealing reduced graphene (ARG) were compared to determine the unique adsorption properties of graphene nanosheets. The adsorption capability of organic pollutants followed the order CRG>ARG>GO, and all three adsorbents showed stronger adsorption to 1-naphthol than to naphthalene. In addition to a π–π interaction, the strong adsorption of 1-naphthol onto graphene nanosheets was mainly attributed to the n–π electron-donor–acceptor (EDA) interactions between the –OH groups of 1-naphthol and the electron-depleted sites on graphene nanosheets. The adsorption of 1-naphthol on reduced graphene materials increased with increasing pH and reached a maximum around its pKa, supporting the n–π EDA interaction mechanism. GO with more functional groups on the nanosheets over CRG and ARG exhibited a strong affinity with Cd2+. The adsorption of Cd2+ onto GO and CRG facilitated the coadsorption of naphthalene and 1-naphthol via surface-bridging mechanisms, such as cation–π interactions. Notably, though ARG showed no significant Cd2+ adsorption, the suppressed coadsorption of naphthalene onto ARG may be attributed to the sieving effect by hydrated Cd2+ binding to the micropore edges on ARG.

Graphene based nanomaterials as chemical sensors for hydrogen peroxide – A comparison study of their intrinsic peroxidase catalytic behavior

In this paper we present for the first time the catalytic activity of N-doped graphene toward a peroxidase substrate oxidation in the presence of hydrogen peroxide. In addition, the activity was compared with that of metallic nanoparticles decorated-graphene, achieved either by catalytic chemical vapor deposition with induction heating (CCVD-IH) or by chemical reduction of graphene oxide (GO). From all investigated graphene-based nanomaterials, the highest activity was exhibited by N-doped graphene and gold nanoparticles supported on chemically-reduced graphene oxide. The steady-state kinetic of the two nanocomposites was carried-out in order to evaluate their peroxidase-mimetic activity. Doping the graphene surface with nitrogen atoms led to a nanomaterial with a better affinity toward hydrogen peroxide compared to the natural enzyme (horseradish peroxidase). Additionally, the systematic study of the catalytic activity for a variety of graphene-based nanomaterials offered important findings for designing new nanomaterials with peroxidase-like activity.

Effect of combined chemical and electrochemical reduction of graphene oxide on morphology and structure of electrodeposited ZnO

This study reports a novel method of tailoring the properties of ZnO nanostructures by electrodeposition in presence of chemically-reduced graphene oxide (rGO). The coupled electrochemical and chemical reduction of graphene oxide resulted in few-layer graphene-based material. The presence of rGO in the electrolytic bath showed a marked influence on the morphology and structure of the hybrid nanostructures. The results indicated the presence of 5mgL−1 rGO results in a 42.9% decrease in resistivity of the hybrid material with respect to the pure ZnO. The proposed approach shows very promising for the fabrication of transparent conductive oxide electrodes.

Hierarchical SnO2 architectures: controllable growth on graphene by atmospheric pressure chemical vapour deposition and application in cataluminescence gas sensor

A facile catalyst-free atmospheric pressure chemical vapour deposition (APCVD) method for the growth of hierarchical SnO2 architectures on graphene is demonstrated. SnO2 2D nanorod arrays, flower@column composites, dendrite structures, and nanoparticles grown on graphene, named as SnO2/graphene architectures, were synthesized on Thermally-Reduced Graphene Oxide (TRGO) and Chemically-Reduced Graphene Oxide (CRGO), respectively. According to characterizations, the rutile SnO2 architectures had large-area uniformity and high crystallinity, which were highly densely and uniformly grown on graphene. A self-catalyzed vapor–solid (VS) and a self-catalyzed vapor–liquid–solid (VLS) mechanisms were proposed based on the detailed observation on the growth behaviour of the SnO2/graphene materials. The synthesized SnO2/graphene materials were directly used to construct gas sensors for methanol detection based on the cataluminescence (CTL) emission. Further study indicated that the SnO2/graphene materials showed enhanced CTL response to methanol and a morphology-dependent CTL performance. And then a fast and highly effective gas sensor for selective detection of methanol was designed based on the SnO2/graphene nanoparticles. The linear range of the methanol gas sensor was 6.3–88.5 μg mL−1, and the detection limit was 5.2 μg mL−1 (S/N = 3).

The Novel Carbon Nanomaterials Electrochemical Sensor for Determination of Trace Aluminum in Human Body Fluids With 8-Hydroxyquinoline

The novel carbon materials modified electrodes are prepared by multi-walled carbon nanotubes (MWNTs) and chemical reduced graphene (CRG) nanosheets. The modified electrodes can detect aluminum(III) in biological samples using 8-hydroxyquinoline (8-HQ) as a sequestering agent. The modified electrodes are characterized by cyclic voltammetry, transmission electron microscopy, and infrared spectrum. The electrochemical behaviors of 8-HQ with and without aluminum at the modified electrodes are investigated by linear scan voltammetry (LSV). The experimental results show the electrochemical activities of the new carbon material modified electrode that are improved greatly and compared with the bare glassy carbon electrode. This novel method is based on the property that LSV anodic peak current of 8-HQ decreases linearly when the concentration of aluminum increases. Under the optimum experimental conditions (pH7.5, 0.1 mol/L Tris-HCl buffer solution, and 2×10-4 mol/L 8-HQ), the linear range and detection limit are 7×10-7 mol/L-8×10-6 mol/L, 3.1×10-7 mol/L for CRG and 7×10-7 mol/L-8×10-6 mol/L, 1.7×10-7 mol/L for MWNT, with 5×10-6 mol/L Al(III). Eight measurements are carried out for each modified electrode, and the relative standard deviation of the results is found to be 2.4% (MWNT) and 3.2% (CRG), respectively. The modified electrode exhibits good stability and is used to detect aluminum concentration in biological fluids, including human serum and cerebrospinal fluid. The recoveries are 87.5%-90.0% for CRG and 92.5%-95.0% for MWNT, respectively.

Small Particles of Chemically-Reduced Graphene with Improved Electrochemical Capacity

Chemically reduced graphenes (CRGs) of different sizes were prepared by the reduction of graphene oxide (GO) in different oxidation degrees, with hydrazine hydrate as the reducing agent. Compared with normally oxidized GO (46.9 wt %), the deeply oxidized GO particles have a higher oxygen content (50.4 wt %). The oxygen content of resulting CRG is correspondingly increased from 11.3 wt % of normal-sized CRG to 16.3 wt % of small-sized CRG, with a dramatic increase in specific surface area from 468.2 to 716.3 m2/g. More graphene edges, which were highly decorated by pseudocapacitive-active sites, were exposed in the small-sized CRG. As a result, small-sized CRG has a much higher specific capacitance (192.1 F/g) than that of normal-sized CRG (132.3 F/g), which is attribute to the contribution of both electrochemical double layer capacitance by an increased surface area and pseudocapacitance by extra surface functional groups.