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A simple and environment friendly protocol has been developed for the synthesis of Ag nanoparticles (AgNPs) supported on reduced graphene oxide (rGO) with copper metal foil as reductant. The prepared AgNPs-rGO, nanocomposite was characterized by various analytical techniques such as scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD). The electrochemical performance of the material has been evaluated using cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The average crystallite size of AgNPs is found to be 32.34 nm. The application of prepared electrocatalyst (AgNPs-rGO) as a non-enzymatic sensor is examined through the modified electrode with the synthesized AgNPs-rGO. The sensor showed excellent performance toward H2O2 reduction with a sensitivity of 12.73 µA.cm-2.mM-1, with a linear dynamic range of 1.5 µM – 100 mM, and the detection limit of 1.90 µM (S/N = 3). Furthermore, the sensor displayed high sensitivity, reproducibility, stability and selectivity for the determination of H2O2. The results demonstrated that AgNPs-rGO has potential applications as sensing material for quantitative determination of H2O2.

A facile hydrothermal method is adopted for the synthesis of hierarchical flowerlike nickel sulfide nanostructure materials and their composite with carbon quantum dot (NiS/C-dot) composite. The composite material exhibited good performance for electrochemical energy-storage devices as supercapacitor with a specific capacity of 880 F g-1 at a current density of 2 A g-1. The material remained stable up to the tested 2000 charge-discharge cycles. Carbon quantum dots of size 1.3 nm were synthesized from natural sources and the favorable electronic and surface property of C-dots were utilized for improvement of the supercapacitor performance of NiS. The results from Tafel analysis, double-layer capacitance, and the impedance measurement reveal that the incorporation of C-dots inside the NiS matrix has improved the charge-transfer process, which is mainly responsible for the enhancement of the supercapacitive property of the composite materials.

Gold nanoparticles (AuNPs) and reduced graphene oxide (RGO) composite modified carbon paste electrode (CPE) was prepared by electrodepositing AuNPs over the reduced graphene oxide (RGO) modified carbon paste electrode. The composite material was characterised using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. The nano composite modified electrode was applied for the determination of total As and for the inorganic speciation of As(III) and As(V) in environmental samples. The linear dynamic range was obtained for the determination of As(III) in the present method from 1μgL−1 to 20 μgL−1 and the limit of detection(LOD) in the standard solution was found to be 0.13 μgL−1 for the 300 sec deposition time in 10 mL supporting electrolyte solution. This method was applied for the determination of As (III) in water and soil samples. The results were agreed well with the result obtained from the hydride generation atomic absorption spectrometry.

In the present investigation, ternary nanocomposite of reduced graphene oxide rGO, Nickel sulphde (NiS) and gold nano cube (rGO/NiS/AuNCs) has been synthesized by adopting a facile single step hydrothermal method. The electrochemical interfacial property of the composite materials is obtained from cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The crystal structure, surface morphology and elemental composition of the rGO/NiS/AuNCs ternary nanocomposite are characterized using XRD, SEM and EDX measurements, the characterization of the materials using such techniques have shown the formation of flower shaped NiS and Au in the form of AuNCs, effective formation of composite has been evident from the microscopic and spectroscopic measurements. The square wave voltammetry technique is employed to the determination of Cr(VI) in 0.1 M acetate buffer solution at the optimized pH 5. The influence of various electrochemical parameters affecting the stripping voltammetry are investigated and optimized. Under optimal condition, the limit of detection (LOD) in the present method is found to be 0.09 µgL−1 at the accumulation potential of -0.5V for the duration of 30s. The rGO/NiS/AuNCs ternary nano composite modified electrode showed good stability and high sensitivity towards the detection of Cr(VI) with low response time. The developed method has been applied for the detection of Cr(VI) in environmental samples.

The variables affecting determination of ultra trace levels of uranium (VI) in aqueous samples by differential pulse cathodic stripping voltammetry using chloranilic acid as the complexing agent have been examined in detail. Effect of organic surfactants on the voltammetric behavior has been studied. Electrochemical impedance measurements reveal the effect of adsorption of different surfactants on the adsorption pre-concentration step of uranium-chloranilic acid complex. Additionally, to better understand the analytical feature of the method, physicochemical aspects of the preconcentration process has been studied. Adsorption of uranium-chloranilic acid complex follows the Langmuir adsorption isotherm. Analysis results on sea water samples from India are reported.

A facile, one-step solvothermal approach has been utilized for the synthesis of a reduced graphene oxide/Au nanocomposite (RGO/Au) material. Deposition of Au nanoparticles (AuNPs) on the surface of reduced graphene oxide sheets has been realized by a simple reduction of Au precursors and graphite oxide (GO) in ethylene glycol (EG), without using any additional reductants and surfactants. The morphology of the RGO/Au nanocomposite was thoroughly examined by X-ray diffraction (XRD), Fourier transform infrared (FIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The morphology of the RGO/Au nanocomposite was characterized by HRTEM and 20 nm was the average size of the AuNPs obtained. The performance of the RGO/Au nanocomposite has been investigated in the application of the Hg determination at the trace/ultra trace level using differential pulse anodic stripping voltammetry. The composite material was also applied for the determination of p-methoxy phenol (PMP) and, most importantly, it was observed that the material was suitable for the decomposition of PMP by the electrochemical oxidation process. The three sigma detection limits for Hg2+ and PMP were obtained as 0.25 mu gL(-1) and 0.64 mu M, respectively. The applicability of the RGO/Au nanocomposite was further extended to determine Hg soil samples. Chronoamperometric tests were carried out to investigate the performance of modified and unmodified electrodes in the decomposition of PMP by the electrochemical oxidation route. (C) 2015 Elsevier Ltd. All rights reserved.

An electrochemical method was developed for the determination of mercury using polycrystalline gold electrode modified by self-assembled monolayers (SAMs) of 2-mercaptobenzothiazole (MBTH). Morphological and electrochemical characterisation of the self-assembled structure of MBTH was performed using atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) measurements. The monolayer of MBTH has shown high affinity for Hg2+. The limit of detection for the determination of Hg2+ using the MBTH SAMs modified gold electrode was obtained as 0.421 μg L−1. The pre-concentration of Hg2+ at open circuit potential is beneficial for the onsite monitoring of mercury concentration in water samples.

Bi-film was deposited on the carbon paste electrode and used as the modified electrode in stripping voltammetry. Bi deposition was carried out ex-situ in acetate buffer solution of pH 4.5 under mild stirring conditions. The deposition potential, deposition time and the Bi-concentration in the deposition solution were optimized and the corresponding values are −0.8 V (SCE), 300 s and 0.3 mM Bi-nitrate solution respectively. A substantial enhancement of an order of magnitude in the sensitivity has been observed when carbon paste electrode was modified with nafion coated carbon nano tube on which Bi-film was deposited. This enhanced sensitivity was attributed to the increased active surface area and also the enhanced charge transfer processes which increased the deposition processes and so the stripping current. Effect of different surfactants on the stripping peak of the heavy metal ions is investigated with and without modification by nafion. Detection limits using Bi-film electrode was obtained for Zn, Cd and Pb as 17.3, 16.9, 11.9 μg L−1, respectively, using Bi-film electrode. Analysis result of two water samples and two ayurvedic medicines are reported.