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Vala A.K.,Maharaja Krishnakumarsinhji Bhavnagar University
Environmental Progress and Sustainable Energy | Year: 2015

Production of gold nanoparticles (GNPs) by biological route was examined using a marine-derived fungal isolate. The isolated strain was identified as Aspergillus sydowii based on morphological traits and molecular identification technique. The test strain exhibited the potential to produce GNPs. A noteworthy observation was that mode of biosynthesis (extracellular/intracellular) depended on supplied gold ion concentration. As revealed by the color of the filtrate, at lower concentrations of gold ion larger size particles were obtained, while higher concentrations supported synthesis of smaller particles. The particles biosynthesized at 3 mM gold chloride were found to be spherical and nearly monodisperse in nature. The particles were found to be in the size range of 8.7-15.6 nm with a mean diameter of 10 nm. Based on the findings it can be concluded that marine-derived fungus A. sydowii could be a promising candidate for synthesizing GNPs using green chemistry approach. Hence, the protocol is ecofriendly. The present study is the first ever report on biosynthesis of GNPs using a marine-derived A. sydowii. © 2014 American Institute of Chemical Engineers.

Vala A.K.,Maharaja Krishnakumarsinhji Bhavnagar University
Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry | Year: 2014

Gold nanoparticles (GNPs) production by the green chemistry approach was examined using a marine-derived fungus Rhizopus oryzae. The test fungi revealed production of gold nanoparticles both, extra and intracellularly. Extracellular biosynthesis was found at the gold chloride concentration 0.25 mM, as evidenced by lavender-purple color of the solution. At other concentrations, intense coloration in biomass was observed indicating intracellular biosynthesis of gold nanoparticles. To the best of the author's knowledge, this is first ever report on extracellular biosynthesis of GNPs by R. oryzae under static condition. Copyright © Taylor & Francis Group, LLC.

Vala A.K.,Maharaja Krishnakumarsinhji Bhavnagar University
BioTechnology: An Indian Journal | Year: 2014

The objective of the work was to explore potential of marine-derived fungi for biosynthesis of gold nanoparticles (GNPs). Three marine-derived fungal isolates viz. Aspergillus candidus, Aspergillus flavus and Aspergillus niger have been examined for their ability to biosynthesize GNPs.All the test isolates were challenged with different concentrations (0.25, 0.5, 1, 2 and 3mM) of gold (III) chloride under static condition at 27°C for 72h. The isolates could biosynthesize spherical GNPs mostly extracellularly. In certain cases,mode of synthesis extra/intracellular was observed to be dependent on gold ion concentrations. While there is no much information available on exploitation of marine-derived fungi for biosynthesis of metal nanoparticles, present findings suggest marinederived fungi as potential resource for developing cost-effective green technology for GNP synthesis. © 2014 Trade Science Inc. - INDIA.

Soni H.R.,Maharaja Krishnakumarsinhji Bhavnagar University | Jha P.K.,M. S. University of Baroda
Solid State Communications | Year: 2014

The present paper reports the calculated vibrational and elastic properties of some two dimensional carbon allotropes such as graphene, α-, β- and γ-graphynes using first principles density functional theory. The phonon modes of graphynes show quite distinct behavior than graphene and have real frequency throughout the Brillouin zone thus indicating dynamically stable structures. The out of plane, ZA mode is more dispersive in the case of graphynes. We have discussed the implications of phonon modes to the thermal conductance in graphynes and graphene. We have also calculated the elastic constants for graphene and graphynes. Calculated elastic constants of graphynes show more anisotropic conformer nature than graphene. © 2014 Elsevier Ltd.

Gupta S.K.,Maharaja Krishnakumarsinhji Bhavnagar University | Gupta S.K.,Michigan Technological University | Jha P.K.,Maharaja Krishnakumarsinhji Bhavnagar University
International Journal of Hydrogen Energy | Year: 2013

We report first-principles pseudopotential method and density functional linear response theory calculations of the structural, electronic, vibrational and thermodynamical properties of LaH2 in fluoride phase at zero and high pressures. The electronic band structure and first time calculated pressure dependent lattice dynamic properties show that the LaH2 is metallic in nature at zero pressure. The pressure dependent electronic band structure calculations show that the bands are closing and reopening with pressure. The phonon mode softens at 11 GPa indicating an instability in lattice structure and pressure induced transverse acoustic phonon mode driven displacive type structural phase transition. The LaH2 also shows weak superconductivity at zero pressure. The valence charge electron density at 46 GPa shows a cage type charge contour and a space where hydrogen can be absorbed and filled easily. There is a considerable charge accumulation in the bonding region of La and H atoms, which strengthens covalent character of LaH 2, and henceforth this material can be one of the best materials for hydrogen storage application at high pressures. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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