Tapas Kuila

Non-covalent functionalization of reduced graphene oxide using sulfanilic acid azocromotrop and its application as a supercapacitor electrode material

Sulfanilic acid azocromotrop (SAC) modified reduced graphene oxide (SAC-RGO) was prepared by simple non-covalent functionalization of graphene oxide (GO) followed by post reduction using hydrazine monohydrate. Spectral analysis (Fourier transform infrared, Raman and X-ray photoelectron spectroscopy) revealed that successful modification had occurred of GO with SAC through π–π interaction. The electrical conductivity of SAC-RGO was found to be ∼551 S m−1. The capacitive performance of SAC-RGO was recorded using a three electrode set up with 1 (M) aqueous H2SO4 as the electrolyte. The –SO3H functionalities of SAC contributed pseudocapacitance as evidenced from the redox peaks (at ∼0.43 and 0.27 V) present in the cyclic voltammetric (CV) curves measured for SAC-RGO. The contribution of electrical double layer capacitance was evidenced from the near rectangular shaped CV curves and resulted in a high specific capacitance of 366 F g−1 at a current density of 1.2 A g−1 for SAC-RGO electrode. An asymmetric device (SAC-RGO//RGO) was designed with SAC-RGO as the positive electrode and RGO as the negative electrode. The device showed an energy density of ∼25.8 W h kg−1 at a power density of ∼980 W kg−1. The asymmetric device showed retention in specific capacitance of ∼72% after 5000 charge–discharge cycles. The Nyquist data of the device was fitted with Z-view and different components (solution resistance, charge-transfer resistance and Warburg elements) were calculated from the fitted curves.

Growth of Ni–Co binary hydroxide on a reduced graphene oxide surface by a successive ionic layer adsorption and reaction (SILAR) method for high performance asymmetric supercapacitor electrodes

A simple, additive-free, cost-effective and scalable successive ionic layer adsorption and reaction (SILAR) method is reported to prepare nickel–cobalt binary hydroxide (Ni–Co–BH) on a reduced graphene oxide (RGO) directing template over a macro-porous conductive nickel foam substrate. This green technique is not only considered as fundamental research interest, but also describes the commercial applications of supercapacitors to reduce the electrode fabrication cost. Three different Ni–Co–BH–G (Ni–Co–BH/RGO) composites are synthesised by tailoring the nickel–cobalt ratios. The flower-like 3D framework of Ni–Co–BH–G provides a porous nano-structure to facilitate the charge transfer and ion diffusion. The cathodic peak current density vs. square root of the scan rate slope values of cyclic voltammetry are consistent with specific capacitance (SC) retention (vs. current density) from charge–discharge curves and the diffusion time constant of the Nyquist plot of the Ni–Co–BH–G composites. Taking the advantage of 3D conductive mesoporous open framework, the Ni–Co–BH–G has provided an excellent SC of 2130 F g−1 at 2 A g−1. An asymmetric supercapacitor device is designed with the optimized Ni–Co–BH–G as the positive electrode and concentrated HNO3 treated conducting carbon cloth (CCN) as the negative electrode. An excellent energy density of ∼92 W h kg−1 and a high power density of ∼7.0 kW kg−1 with lifetime stability up to 10000 charge–discharge cycles (capacitance retention ∼ 80%) are provided by the asymmetric device. Four asymmetric devices have been assembled in series, which provided ∼5.6 V charge–discharge potential. The assembled system has powered a 5 V light-emitting diode (LED) successfully.

Development of high energy density supercapacitor through hydrothermal synthesis of RGO/nano-structured cobalt sulphide composites.

Co9S8/reduced graphene oxide (RGO) composites were prepared on nickel foam substrate through hydrothermal reaction and used directly as supercapacitor electrode. The field emission scanning electron microscopy analysis of the composites showed the formation of Co9S8 nano-rods on the RGO surfaces. The average crystal size of the Co9S8 nano rods grown on the RGO sheets were ∼25-36 nm as calculated from x-ray diffraction analysis. The reduction of graphene oxide (GO) was confirmed by Raman and x-ray photoelectron spectroscopy analysis. The electrical conductivity of the Co9S8/RGO composite was recorded as 1690 S m(-1) at room temperature, which is much higher than that of pure GO further confirming the hydrothermal reduction of GO. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were investigated to check the electrochemical performances of the Co9S8/RGO composites. The Co9S8/RGO composites supported on nickel foam showed very high specific capacitance (Sc)(1349 F g(-1) at a current density of 2.2 A g(-1)), energy density (68.6 W h kg(-1)) and power density (1319 W kg(-1)) in 6 M KOH electrolyte. The retention in Sc of the composite electrode was found to be ∼96% after 1000 charge-discharge cycles.

Enhanced mechanical properties of a multiwall carbon nanotube attached pre-stitched graphene oxide filled linear low density polyethylene composite

A synergetic effect of multiwall carbon nanotube (MWCNT) attached pre-stitched graphene oxide (GO) on the mechanical properties of its linear low density polyethylene (LLDPE) composite was demonstrated. The reduction, functionalization and stitching of GO occurred simultaneously with the amine (–NH2) functionalities of ethylenediamine through nucleophilic addition and condensation reaction. The structural features of MWCNT attached pre-stitched GO with ethylenediamine (EtGO) (EtGO–MWCNT) hybrids were confirmed by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. The EtGO–MWCNT hybrid filled LLDPE composite was prepared by solution mixing. The tensile strength of the EtGO–MWCNT/LLDPE composite with 1 wt% loading was enhanced by 148.7% compared to that of the neat LLDPE, which is much higher than those of O-MWCNTs, GO and EtGO filled composites. The enhanced properties of the EtGO–MWCNT/LLDPE composites were attributed to the homogeneous dispersion and the enhanced interfacial interaction with the matrix due to the multi-dimensional structure of EtGO–MWCNT. The EtGO–MWCNT/LLDPE composite also showed better dimensional stability than those of O-MWCNTs, GO, and EtGO filled composites.

Electrochemical performance of reduced graphene oxide surface-modified with 9-anthracene carboxylic acid

An efficient approach for the preparation of 9-anthracene carboxylic acid (ACA) modified reduced graphene oxide (rGO) was demonstrated in this study. ACA was used as a surface-modifying agent and underwent a reversible redox reaction. The benzene ring of the ACA anion was attached to the rGO surface via π–π interactions, and the carboxylate anions helped to disperse the hybrid materials in water due to hydrogen bonding. Therefore, water-dispersible, ACA-modified rGO (ACA-rGO) improved the wettability and capacitance performance in aqueous electrolyte solutions. The morphology of the ACA-rGO was studied using transmission electron microscopy and atomic force microscopy image analysis. The dispersion characteristics of the exfoliated materials were investigated using UV-vis spectroscopy analysis. The chemical states and natures of the samples were investigated using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). The appearance of a new peak at 288.7 eV in the XPS of ACA-rGO confirmed the successful surface modification of rGO using ACA. Raman spectra were studied to compare the electronic structure and defect concentrations in the ACA-rGO with respect to GO. The low intensity and shifted D- and G-bands indicated non-covalent functionalization of rGO with ACA anions. Electrochemical performances of ACA-rGO, rGO, and GO were evaluated in 1 M aqueous Na2SO4 electrolyte. The capacitance performance was investigated through galvanometric charge–discharge with ACA-rGO, rGO, and GO in an operating voltage of −1 to 1 V. The range of specific capacitance in the three-electrode system was 610 to 115 F g−1 at a current density range of 0.8 to 20 A g−1. In addition, the capacitance performance of ACA-rGO was studied in 1 M Na2SO4 electrolyte using two-electrode systems. The cell capacitance, energy density, and power density at a current density of 0.2 A g−1 of the asymmetric assembly with multiwall carbon nanotubes were 77 F g−1, 41.3 Wh kg−1, and 200 W kg−1, respectively.

Electrochemically Preparation of Functionalized Graphene Using Sodium Dodecyl Benzene Sulfonate (SDBS)

Preparation of functionalized graphene by electrochemical exfoliation of graphite rod using sodium dodecyl benzene sulfonate (SDBS) is reported. SDBS solution has been used as the electrolyte as well as functional groups. SDBD is an anionic surfactant which helps to provide uniform dispersion in water and prevents the π-π π-π stacking as well. XRD result indicates the formation of graphene whereas; the functionalization of graphene was confirmed through the FT-IR spectrum, which shows presence of peaks corresponding to SO3-. UV-vis spectroscopy demonstrates the dispersibility of SDBS-functionalized graphene, and peaks of SDBS and graphene appeared at 225 nm and 260nm, respectively. Raman spectroscopy show ID/IGIDIG ratio is < 1. It means that defects of SDBS-functionalized graphene are reduced.

Static and Dynamic Mechanical Properties of Graphene Oxide-Incorporated Woven Carbon Fiber/Epoxy Composite

This study investigates the synergistic effects of graphene oxide (GO) on the woven carbon fiber (CF)-reinforced epoxy composites. The GO nanofiller was incorporated into the epoxy resin with variations in the content, and the CF/epoxy composites were manufactured using a vacuum-assisted resin transfer molding process and then cured at 70 and 120xa0°C. An analysis of the mechanical properties of the GO (0.2xa0wt.%)/CF/epoxy composites showed an improvement in the tensile strength, Young’s modulus, toughness, flexural strength and flexural modulus by ~xa034, 20, 83, 55 and 31%, respectively, when compared to the CF/epoxy composite. The dynamic mechanical analysis of the composites exhibited an enhancement of ~xa056, 114 and 22% in the storage modulus, loss modulus and damping capacity (tanδ), respectively, at its glass transition temperature. The fiber–matrix interaction was studied using a Cole–Cole plot analysis.

Morphology controlled synthesis of MnCO3–RGO materials and their supercapacitor applications

MnCO3-reduced graphene oxide (MnCO3–RGO) was grown on nickel foam by a facile successive ionic layer adsorption and reaction (SILAR) method and used as a supercapacitor electrode. The morphology of the MnCO3 functionalities was tuned from lotus to flake to spherical shape using different chelating agents during synthesis. The length and width of the individual petals of the lotus structure MnCO3 were found to be ∼200–300 and 50–100 nm, respectively. The reduction of graphene oxide (GO) in MnCO3–RGO composites was confirmed by Raman spectroscopy and electrical conductivity data analysis. The lotus shaped MnCO3 grown on RGO sheets provided a high surface area and electrical conductivity as compared to the developed electrode materials. The cyclic voltammetry, galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy analyses showed that the lotus shaped MnCO3 grown on RGO sheets provided higher current response, large specific capacitance (SC) and low solution, charge-transfer and Warburg resistance as compared to the flake and spherically shaped MnCO3 grown on RGO sheets. A fabricated asymmetric supercapacitor (ASC) device with MnCO3 (lotus) – RGO as the positive electrode and sonochemically reduced GO as the negative electrode – exhibited a working potential of ∼0–1.6 V, SC of ∼ 335 F g−1 at ∼2 A g−1 (∼468 mF cm−2 at ∼2.8 mA cm−2), an energy density of ∼120 W h kg−1 (∼0.16 mW h cm−2) and a power density of ∼16 kW kg−1 (∼22 mW cm−2) with a GCD stability of ∼73% after 10u2006000 cycles.

Investigation of mechanical and thermal properties of the cetyltrimethylammonium bromide functionalized molybdenum disulfide (MoS2)/epoxy composites

Molybdenum disulfide (MoS2), a 2D layered material has been recognised as a new paradigm in the area of materials science due to its graphene like structure. Herein, we prepared functionalized MoS2 nanosheets through one-pot hydrothermal technique using cationic surfactant, cetyltrimethylammonium bromide (CTAB). The surfactant functionalized MoS2 (CTAB-MoS2) was subsequently dispersed in epoxy matrix at the loading level of 0.1–0.5 wt% to investigate the reinforcing competence of MoS2 on the mechanical and thermal properties of the composites. Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy (FE-SEM) were used to characterize the microstructure and morphology of the hydrothermally prepared pristine MoS2 and CTAB-MoS2. Dynamic mechanical and tensile properties were studied to comprehend the effect of functionalized MoS2 on the mechanical properties of the composites. At 0.2 wt% loading, the tensile strength and Young’s modulus was improved by ~23 and 26.7%, respectively, while ~83% improvement in storage modulus was recorded. Thermal stability of all the studied specimens were compared by selecting the temperatures at 10 and 50% weight losses which showed small decrease in onset degradation temperature.

Novel synthesis of a Cu2O–graphene nanoplatelet composite through a two-step electrodeposition method for selective detection of hydrogen peroxide

An optimized two-step electrochemical deposition technique for the synthesis of a Cu2O/graphene platelet composite from copper acetate and a graphite rod is demonstrated. In the first step, graphene nanoplatelets were electrodeposited onto a stainless steel substrate from the graphite rod and then Cu2O NPs from copper acetate solution were electrodeposited onto the same electrode through the second electrodeposition step. Raman spectroscopy and X-ray photoelectron spectroscopy were performed to confirm the quality of the graphene nanoplatelets produced. X-ray diffraction studies revealed the successful formation of Cu2O nanoparticles. Transmission electron microscopy and field emission scanning electron microscopy were carried out to study the morphology, and the microscopic images revealed that the graphene surfaces were evenly anchored with Cu2O nanoparticles. The electrocatalytic behavior of the Cu2O/graphene platelet composite was analysed through cyclic voltammetry, differential pulse voltammetry and amperometric studies. The electrochemical studies revealed the utilization of the prepared material for non-enzymatic electrochemical sensing of H2O2. The amperometric studies showed the sensitivity and limit of detection of the prepared Cu2O/graphene platelet composite to be 52.8595 μA μM−1 cm−2 and 34.32 nM, respectively.