T. V. Venkatesha

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.

An amperometric bienzymatic cholesterol biosensor based on functionalized graphene modified electrode and its electrocatalytic activity towards total cholesterol determination.

Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been covalently immobilized onto functionalized graphene (FG) modified graphite electrode. Enzymes modified electrodes were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). FG accelerates the electron transfer from electrode surface to the immobilized ChOx, achieving the direct electrochemistry of ChOx. A well defined redox peak was observed, corresponding to the direct electron transfer of the FAD/FADH(2) of ChOx. The electron transfer coefficient (α) and electron transfer rate constant (K(s)) were calculated and their values are found to be 0.31 and 0.78 s(-1), respectively. For the free cholesterol determination, ChOx-FG/Gr electrode exhibits a sensitive response from 50 to 350 μM (R=-0.9972) with a detection limit of 5 μM. For total cholesterol determination, co-immobilization of ChEt and ChOx on modified electrode, i.e. (ChEt/ChOx)-FG/Gr electrode showed linear range from 50 to 300 μM (R=-0.9982) with a detection limit of 15 μM. Some common interferents like glucose, ascorbic acid and uric acid did not cause any interference, due to the use of a low operating potential. The FG/Gr electrode exhibits good electrocatalytic activity towards hydrogen peroxide (H(2)O(2)). A wide linear response to H(2)O(2) ranging from 0.5 to 7 mM (R=-0.9967) with a sensitivity of 443.25 μA mM(-1) cm(-2) has been obtained.

Preparation of self assembled sodium oleate monolayer on mild steel and its corrosion inhibition behavior in saline water.

A self assembled monolayer (SAM) of sodium oleate was generated on mild steel by the dip coating method. Formation of the SAM on mild steel was examined using Infrared Reflection Absorption Spectroscopy (IRRAS) and contact angle measurements. The chemical and anticorrosive properties of the SAM were analyzed using different techniques. IRRAS and water contact angle data revealed the crystallinity and chemical stability of the SAM modified mild steel. The electrochemical measurements showed that the mild steel with the sodium oleate derived SAM exhibited better corrosion resistance in saline water. The effect of temperature and pH on the SAM formation and its anti corrosion ability was explored.

Electrodeposition and corrosion behavior of Zn–Ni and Zn–Ni–Fe2O3 coatings

A thin film of Zn–Ni–Fe2O3 on steel substrates was prepared by electrodeposition technique using Zn–Ni alloy plating solution with nano-sized Fe2O3 particles. The cathodic polarization and cyclic voltammetry techniques were used to explain deposition process. The corrosion behavior of deposits was evaluated by polarization and impedance studies. Scanning electron microscope (SEM) images were used to study the surface morphology of coating. The grain size and amount of Fe2O3 particles present in composite coating were measured by X-ray diffraction pattern (XRD) and energy dispersive X-ray diffraction spectrometer (EDS), respectively.

Electrochemical Synthesis and Photocatalytic Property of Zinc Oxide Nanoparticles

Zinc oxide (ZnO) nanoparticles of varying sizes (20, 44 and 73 nm) have been successfully synthesized by a hybrid electrochemical-thermal method using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The as-synthesized product was characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Scanning electron microscopy along with Energy dispersive analysis of X-ray (SEM/EDAX), Transmission electron microscopy (TEM), Ultra Violet - Diffuse reflectance spectroscopic methods (UV-DRS). and UV-DRS spectral methods. The as-synthesized compound were single-crystalline and Rietveld refinement of calcined samples exhibited hexagonal (Wurtzite) structure with space group of P63mc (No.186). The band gaps for synthesized ZnO nanoparticles were 3.07, 3.12 and 3.13 eV, respectively, based on the results of diffuse reflectance spectra (DRS). The electrochemically synthesized ZnO powder was used as photocatalysts for UV-induced degradation of Methylene blue (MB). Photodegradation was also found to be function of exposure time and dye solution pH. It has been found that as-synthesized powder has excellent photocatalytic activity with 92% degradation of MB, indicating ZnO nanoparticles can play an important role as a semiconductor photocatalyst.

Studies on electrodeposition of Zn–MoS2 nanocomposite coatings on mild steel and its properties

Pure zinc and Zn–MoS2 composite coatings were prepared by electrodeposition from zinc sulfate–chloride bath containing uniformly dispersed MoS2 nanoparticles. The effect of MoS2 on the deposition properties morphology, crystallographic orientation, and corrosion behavior were studied. The electrokinetic properties (zeta potential) and size distribution statistics in plating bath for the particles were evaluated using dynamic light scattering experiments. The Zn and Zn–MoS2 deposition process was studied by linear polarization and cyclic voltammetry. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and potentiodynamic polarization measurements were used to characterize the coatings. The addition of MoS2 to the electrolyte significantly changed the microstructure and crystallographic orientation of the zinc deposits and enhanced the corrosion resistance of the coatings. The morphological and electrochemical properties of the zinc coatings were observed to be significantly affected by the incorporation of MoS2 particles into the zinc matrix.

The fabrication, characterization and electrochemical corrosion behavior of Zn-TiO2 composite coatings

Metal-nanoparticle composite coatings improve the hardness, wear resistance and corrosion resistance properties of metal coatings. In this work, TiO2 nanoparticles were chosen as second-phase particles to generate anticorrosive Zn composite coatings. The TiO2 nanoparticles were dispersed in a Zn plating solution to co-deposit them with Zn. The Zn-TiO2 composite coatings were then characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction methods. The presence of TiO2 particles in the composite was confirmed by SEM images and EDS spectra. The Zn-TiO2 composite coatings incorporated with different amounts of TiO2 particles were tested for corrosion performance by polarization and electrochemical impedance spectroscopy, and the dissolution behavior of the coatings that had been immersed in corrosive media for a long time was studied. Improved corrosion resistance properties of the Zn-TiO2 composite coatings were confirmed by polarization studies, fitted Nyquist plots, an increase in phase angle and a shift in the Rct characteristic peak of the Bode plot.

Studies on the preparation and properties of electroless Ni–W–P alloy coatings and its nano-MoS2 composite

The electroless Ni–W–P ternary alloy and its MoS2 composite films were successfully obtained on low-carbon steel by the electroless plating technique. The sodium tungstate concentration in the bath was varied to obtain Ni–W–P deposits containing various W and P contents. Ni–W–P–MoS2 composite was obtained with a suitable concentration of sodium tungstate in the plating bath. These deposits were characterized via x-ray diffraction (XRD), scanning electron microscopy and energy dispersive XRD spectroscopy studies. The corrosion behavior was investigated via potentiodynamic polarization and electrochemical impedance spectroscopy studies in a 3.5 wt% NaCl solution. An increase in codeposition of the alloying metal tungsten changed the structure and morphology of the deposits and enhanced the corrosion resistance. Mechanical properties such as microhardness and friction coefficients were evaluated. Ni–W–P deposits with increasing amounts of tungsten metal were found to possess higher friction coefficients. The microhardness was greatly improved with increasing codeposition of tungsten metal in the alloy. The incorporation of MoS2 nanoparticles into Ni–W–P alloy coatings strongly influenced in reducing the corrosion and friction.

Pulse Electrodeposition, Characterization, and Corrosion Behavior of Ni-Si3N4 Composites

Ni and its composite (Ni–Si3N4) electrodeposits were successfully obtained on mild steel substrate by the electrodeposition technique. The presence of Si3N4 particles in the deposit was analyzed by an energy dispersive x-ray diffraction (EDAX) spectrometer. The structure and surface morphology of the coatings were analyzed with x-ray diffraction (XRD) and scanning electron microscopy. The changes in the preferred orientation of nickel in the presence of Si3N4 particles were obtained by calculating the texture coefficient from XRD data. The hardness of the deposit was measured using a Vickers microhardness indenter. The antifriction properties of deposits were also discussed. The corrosion behavior of the bare Ni and its composite coatings in 3.5% NaCl were analyzed by polarization and impedance techniques.

Anticorrosion Performance of Electrochemically Produced Zn-1% Mn-Doped TiO2 Nanoparticle Composite Coatings

The Zn-TiO2 composite coatings were electrodeposited on mild steel using sulfate plating bath dispersed with 1% Mn-doped TiO2 nanoparticles. The agglomeration state and charge on the particles in plating condition were analyzed by zeta potential and particle size distribution measurements. The change in microstructure and morphology in composite coatings was analyzed by x-ray diffraction, energy-dispersive x-ray diffraction, and Scanning electron microscopic analyses. The corrosion behavior of the coatings was tested by electrochemical methods such as Tafel polarization and Electrochemical Impedance study. The increased charge transfer resistance with reduced corrosion rate was observed for composite coatings compared to pure zinc coating. The morphology and corrosion behavior of the composite coatings are correlated with pure zinc coating properties.