Venugopal Velmurugan

Co9S8 nanoflakes on graphene (Co9S8/G) nanocomposites for high performance supercapacitors

Co9S8/graphene nanocomposites (Co9S8/G) at various concentrations of graphene and Co9S8 were prepared by a simple chemical route from cobalt nitrate and graphene as precursors in the presence of PVP as surfactant and thioacetamide (TAA) as sulfur source. To gain knowledge about the structural, morphological and physical properties, the composite material was analyzed by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric Analysis (TGA). SEM measurements showed the presence of well dispersed, ∼300 nm sized Co9S8 nanoflakes. To assess the properties of the nanocomposites for their applicability in supercapacitors, electrochemical analysis was carried out in 6 M KOH electrolyte. A maximum specific capacitance of 808 F g−1 was observed for Co9S8/G-d at 5 mV s−1 scan rate. Galvanostatic charge–discharge curves showed the excellent cyclic stability of Co9S8/G-d composite with higher charge–discharge duration than pure Co9S8. The excellent electrochemical performance of the composite could be due to the better electrical conductivity behavior of graphene on Co9S8 nanoflakes.

Synthesis of Cobalt Sulfide–Graphene (CoS/G) Nanocomposites for Supercapacitor Applications

Cobalt sulfide (CoS) and graphene nanocomposites were prepared from cobalt nitrate, thioacetamide, and graphene as starting materials in the presence of poly(vinylpyrrolidone) as surfactant. Furthermore, its morphology and properties were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope, diffusive reflectance ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and electrochemical measurements. The XRD reveals the amorphous nature of the nanocomposites. The as-prepared nanocomposites were tested for its supercapacitance property by cyclic voltammetric (CV) experiment in 6M KOH electrolyte. CV was performed at a potential range of 0 to -0.8 V at different scan rates, and results show an excellent capacitive behavior of the nanocomposites. A maximum specific capacitance of 2423.3 F/g was obtained at a scan rate of 5 mV/s.

CoFe2O4 and NiFe2O4@graphene adsorbents for heavy metal ions – kinetic and thermodynamic analysis

Magnetic cobalt and nickel ferrites (CoFe2O4 & NiFe2O4) with graphene nanocomposites (CoFe2O4–G & NiFe2O4–G) were synthesized via a solvothermal process and used as an adsorbent for the removal of lead (Pb(II)) and cadmium (Cd(II)) ions from aqueous solution. The as-prepared materials were characterized by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), a Brunauer–Emmett–Teller (BET) surface area analyzer, transmission electron microscopy (TEM) and VSM analysis. To probe the nature of the adsorbent, various experiments were investigated like contact time, adsorbent dose, solution pH and temperature were optimized. The isotherm model fitting studies demonstrated that the data fitted the Langmuir isotherm model well. The highest adsorption equilibrium for Pb(II) is 142.8 and 111.1 mg g−1 at pH of 5 and 310 K for CoFe2O4–G & NiFe2O4–G; while for Cd(II) it was 105.26 and 74.62 mg g−1 at pH of 7 and 310 K. The results show that such type of materials could be used for the removal of heavy metal ions from water for environmental applications.

Graphene/Gold Nanocomposites-Based Thin Films as an Enhanced Sensing Platform for Voltammetric Detection of Cr(VI) Ions

A highly sensitive and selective Cr(VI) sensor with graphene-based nanocomposites film as an enhanced sensing platform is reported. The detection of chromium species is a challenging task because of the different possible oxidation states in which the element can occur. The sensing film was developed by homogenously distributing Au nanoparticles (AuNPs) onto the two-dimensional (2D) graphene nanosheet matrix by electrochemical method. Such nanostructured composite film platforms combine the advantages of AuNPs and graphene nanosheets because of the synergistic effect between them. This effect greatly facilitates the electron-transfer processes and the sensing behavior for Cr(VI) detection, leading to a remarkably improved sensitivity and selectivity. The interference from other heavy metal ions is studied in detail. Such sensing elements are very promising for practical environmental monitoring applications.

Combustion Synthesis of Graphene from Waste Paper for High Performance Supercapacitor Electrodes

Incessant streak of unsuccessful attempts to synthesize low cost graphene with larger flake size and purity is frequently reported. Any reported methods that result in few layers of graphene with minimal contamination are definitive to exist. In this work, graphene was prepared economically from source of “paper” and detailed investigation was done on the effect of synthesizing parameters like paper source, temperature and amount of urea in the formation of graphene. This is a cost effective method, in which the paper that we use in our daily life was carbonized with the help of urea at a temperature of 850∘C under N2 atmosphere. The paper source was varied, shape of the paper was altered and the graphene paper with large surface area was synthesized without smudging and the prepared graphene paper was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) for its structural, morphological investigation. To test the supercapacitance performance, electrochemical behavior was investigated i...