Valarselvan S.,Hh The Rajahs College |
Manisankar P.,Alagappa University
Electrochimica Acta | Year: 2011
The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O 2 to H 2O 2. pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O 2 reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry. © 2011 Elsevier Ltd. All rights reserved.
Muthu Kumaran S.,Hh The Rajahs College
Journal of Alloys and Compounds | Year: 2012
In situ ultrasonic measurements have been carried out in a 2024 Al-Cu-Mg alloy heat treated from 300 to 623 K. Different specimens have been prepared by (i) solution annealed at 766 K for 1 h, and (ii) water quenched then aged at 463 K for 10 h or 32 h. High temperature ultrasonic measurements from 300 to 623 K reveal the three transitions, (i) formation of GPB zone around 346 K, (ii) dissolution of GPB zones and S″ phase at 492 K, and (iii) the formation of semi-coherent S′ phase at 557 K which have been confirmed by DSC studies and SEM/TEM characterization. The different phase transformations and dissolutions at high temperature have been explained by the ultrasonic method and are compared to DSC and characterization with TEM. The first and second differential plot of the ultrasonic parameters with respect to temperature is identified as an effective tool in clearly identifying the fine scale precipitation/dissolution events. © 2012 Elsevier B.V. All rights reserved.
Kumaran S.M.,Hh The Rajahs College |
Gopalakrishnan R.,P.A. College
Journal of Sol-Gel Science and Technology | Year: 2012
Ce doped ZnO nanoparticles (Zn 1-xCe xO, x = 0.0, 0.05 and 0.1) have been synthesized by sol-gel method at annealing temperature of 500 °C for 1 h under Ar atmosphere. The synthesized samples have been characterized by powder X-ray diffraction (XRD), energy dispersive X-ray studies, UV-Visible spectrophotometer and fourier transform infrared (FTIR) spectroscopy. The XRD measurements indicate that the prepared nanoparticles have a hexagonal wurtzite structure and CeO 2 crystallites. The calculated average crystalline varied from 21.97 to 15.62 nm with increase in Ce concentrations. The increase in lattice parameters reveals the substitution of Ce into ZnO lattice. The presence of functional groups and the chemical bonding is confirmed by FTIR spectra. PL spectra of the Zn 1-xCe xO system show that the shift in near band edge emission from 386 to 363 nm and a shift in blue band emission from 517 to 485 nm which confirms the substitution of Ce into the ZnO lattice. © Springer Science+Business Media, LLC 2012.
Gopalakrishnan R.,Oxford Engineering College |
Muthukumaran S.,Hh The Rajahs College
Journal of Materials Science: Materials in Electronics | Year: 2013
Zn1-xNixO (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) nanoclusters have been successfully synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV-visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD and SEM measurements reveal that the prepared undoped and Ni-doped nanoclusters have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystalline size from XRD measurement decreases from 37.5 to 26.6 nm for x = 0 to 0.05 which was confirmed by SEM micrographs. The change in lattice parameters, micro-strain, shift of XRD peaks and the blue shift of energy gap from 3.18 to 3.33 eV (ΔEg = 0.15 eV) for Ni = 0-0.02 and red shift of Eg from 3.33 to 3.14 eV (ΔEg = 0.19 eV) for Ni = 0.02 to 0.05 reveal the substitution of Ni2+ ions into Zn-O lattice. The presence of functional groups and the chemical bonding are confirmed by FTIR spectra. The shift of NBE UV emission between 374 and 395 nm, the shift of green band emission between 517 and 531 nm, the change in intensity and the broadening effect in the photoluminescence spectra confirms the substitution of Ni 2+ ions into the Zn-O lattice. Ni-doped ZnO system shows a great pledge for the fabrication of nano-optoelectronic devices like tunable light emitting diode in the near future. © 2012 Springer Science+Business Media, LLC.
Muthukumaran S.,Hh The Rajahs College |
Gopalakrishnan R.,Oxford Engineering College
Physica B: Condensed Matter | Year: 2012
Un-hydrogenated and hydrogenated Cu, Co co-doped ZnO (Zn 0.96-xCo 0.04Cu xO, x=0.03, 0.04 and 0.05) nanopowders have been synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV-Visible spectrophotometer and Fourier transform infrared spectroscopy. The calculated average crystalline size increases from 37.3 to 50.6 nm for un-hydrogenated samples from x=0.03 to 0.05 and it changes from 29.4 to 34.9 nm for hydrogenated samples. The change in lattice parameters, micro-strain, a small shift of X-ray diffraction peaks towards lower angles and reduction in energy gap reveal the substitution of Cu 2 ions into Zn-Co-O lattice. The hydrogenation effect reduces the particle size and induces the more uniform distribution of particles than the un-hydrogenated samples which is confirmed by SEM micrographs. Photoluminescence spectra of Zn 0.96-xCo 0.04Cu xO system shows that red shift in near band edge ultraviolet emission from 393 to 403 nm with suppressing intensity and a blue shift in green band emission from 537 to 529 nm with enhancing intensity confirms the substitution of Cu into the Zn-Co-O lattice. © 2012 Elsevier B.V. All rights reserved.