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Ajmer, India

Mehta S.K.,Panjab University | Kumar S.,Government College | Gradzielski M.,TU Berlin
Journal of Colloid and Interface Science | Year: 2011

The interaction between organic molecules and the surface of nanoparticles (NPs) strongly affects the size, properties and applications of surface-modified metal sulfide semiconductor nanocrystals. From this viewpoint, we compared the influence of cationic surfactants with various chain lengths and anionic surfactants with different head groups, as surface modifiers during synthesis of ZnS NPs in aqueous medium. The surfactant adsorbs on the surface of the particles as micelle-like aggregates. These aggregates can form even at the concentration lower than critical micelle concentration (cmc) due to interaction between the polar groups and the NPs. The nature of interaction depends specifically on the surfactant polar group. The ability of surfactant to form the micelle-like aggregates on the surface of the NPs correlates with their cmc. This leads to the fact that the surfactant with longer tail stabilizes the NPs better since its cmc is lower. The adsorption of the surfactant on the NPs also stabilizes them by the change of their charge which is in accordance with the correlation of zeta potential with the particles stability. The energetics of surface states generating interesting photoluminescence (PL) properties in ZnS NPs has been governed by the nature of surfactant molecules. In general, the size, structure, and stability of the ZnS NPs can be controlled by the choice of suitable surfactant. © 2011 Elsevier Inc.

Subrahmanyam A.,Indian Institute of Technology Madras | Biju K.P.,Government College | Rajesh P.,Indian Institute of Technology Madras | Jagadeesh Kumar K.,Indian Institute of Technology Madras | Raveendra Kiran M.,Indian Institute of Technology Madras
Solar Energy Materials and Solar Cells | Year: 2012

Photocatalysis phenomena in TiO 2 have been under intense investigation for its potential applications in pollution abatement and in production of hydrogen for green energy. Present study shows that surface modification is a potential technique to achieve efficient and stable plasmonic assisted sun light driven photocatalyst with TiO 2 thin films. A few layers (of different thicknesses) of metallic silver have been deposited (by DC magnetron sputtering technique and subsequently annealed) on the surface of sol-gel processed and spin coated TiO 2 thin films. The photocatalytic activity (PCA) has been measured with 254 nm, 352 nm and actual sun light excitations; aqueous Rhodamine B (RhB) dye is used to estimate the photocatalytic oxidation. The photocatalytic activity has been expressed as the number of RhB molecules oxidized for a given photon flux at the excitation wavelength; also rate constants have been evaluated. It is observed that (i) silver exists in the metallic state on the surface of TiO 2 thin films, (ii) the surface work function of TiO 2 thin films is modified by the silver as revealed by Kelvin probe measurements and (iii) the PCA of silver modified TiO 2 thin films is higher in comparison with unmodified surface. An attempt has been made to explain the higher activity of the surface modified Ag/TiO 2 thin film photocatalyst through the plasmon assisted photocatalytic process. The present study clearly establishes the view that surface modification of TiO 2 is a viable approach towards achieving an efficient sun light photocatalyst. © 2012 Elsevier B.V. All rights reserved.

John R.P.,INRS - Institute National de la Recherche Scientifique | Anisha G.S.,Government College | Nampoothiri K.M.,Indian National Institute for Interdisciplinary Science and Technology | Pandey A.,Indian National Institute for Interdisciplinary Science and Technology
Bioresource Technology | Year: 2011

Population outburst together with increased motorization has led to an overwhelming increase in the demand for fuel. In the milieu of economical and environmental concern, algae capable of accumulating high starch/cellulose can serve as an excellent alternative to food c rops for bioethanol production, a green fuel for sustainable future. Certain species of algae can produce ethanol during dark-anaerobic fermentation and thus serve as a direct source for ethanol production. Of late, oleaginous microalgae generate high starch/cellulose biomass waste after oil extraction, which can be hydrolyzed to generate sugary syrup to be used as substrate for ethanol production. Macroalgae are also harnessed as renewable source of biomass intended for ethanol production. Currently there are very few studies on this issue, and intense research is required in future in this area for efficient utilization of algal biomass and their industrial wastes to produce environmentally friendly fuel bioethanol. © 2010 Elsevier Ltd.

Malashetty M.S.,Gulbarga University | Swamy M.S.,Government College
Physics of Fluids | Year: 2011

The combined effect of gravity modulation and rotation on the onset of thermal convection in a horizontal fluid layer and a fluid-saturated porous layer is studied analytically using linear stability theory. The regular perturbation method based on small amplitude of modulation is employed to compute the critical value of Rayleigh number and wavenumber. We considered in the present paper only synchronous mode. The correction critical Rayleigh number is calculated as a function of Taylor number, Prandtl number, Darcy number, frequency of the modulation, normalized porosity, and viscosity ratio. It is shown that in general the gravity modulation produces a stabilizing effect in case of viscous fluid layer and both destabilizing and stabilizing effects in case of Brinkman porous layer while it produces a destabilizing effect in case of Darcy porous layer. The low frequency gravity modulation is found to have a significant effect on the stability of the system. It is shown that the onset of convection can be advanced or delayed by proper tuning of various governing parameters. The results of Darcy limit and viscous flow limit are derived as the degenerate cases of Brinkman model. © 2011 American Institute of Physics.

Subhas Abel M.,Gulbarga University | Tawade J.V.,Gulbarga University | Nandeppanavar M.M.,Government College
Meccanica | Year: 2012

In the present work, the effect of MHD flow and heat transfer within a boundary layer flow on an upper-convected Maxwell (UCM) fluid over a stretching sheet is examined. The governing boundary layer equations of motion and heat transfer are non-dimensionalized using suitable similarity variables and the resulting transformed, ordinary differential equations are then solved numerically by shooting technique with fourth order Runge-Kutta method. For a UCM fluid, a thinning of the boundary layer and a drop in wall skin friction coefficient is predicted to occur for higher the elastic number. The objective of the present work is to investigate the effect of Maxwell parameter β, magnetic parameter Mn and Prandtl number Pr on the temperature field above the sheet. © 2011 Springer Science+Business Media B.V.

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