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Subbarao U.,Jawaharlal Nehru Centre for Advanced Scientific Research | Marakatti V.S.,Jawaharlal Nehru Centre for Advanced Scientific Research | Amshumali M.K.,Jawaharlal Nehru Centre for Advanced Scientific Research | Amshumali M.K.,Vijayanagara Sri Krishnadevaraya University | And 4 more authors.
Journal of Solid State Chemistry | Year: 2016

Facile and efficient ball milling and polyol methods were employed for the synthesis of nickel selenide (NiSe) nanoparticle. The particle size of the NiSe nanoparticle has been controlled mechanically by varying the ball size in the milling process. The role of the surfactants in the formation of various morphologies was studied. The compounds were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy (EDS). The efficiency of the NiSe nanoparticle as a catalyst was tested for the reduction of para-nitroaniline (PNA) to para-phenyldiamine (PPD) and para-nitrophenol (PNP) to para-aminophenol (PAP) using NaBH4 as the reducing agent. Particle size, morphology and the presence of surfactant played a crucial role in the reduction process. © 2016 Elsevier Inc.

Jayaramulu K.,Jawaharlal Nehru Centre for Advanced Scientific Research | Datta K.K.R.,Nanomaterials and Catalysis Laboratory | Suresh M.V.,Jawaharlal Nehru Centre for Advanced Scientific Research | Kumari G.,CPMU | And 4 more authors.
ChemPlusChem | Year: 2012

MOF for effective stabilizer for "Pd" and selective host for CO2: A porous, layered MOF system {[ZnACHTUNGTRENUNG(Himdc)- ACHTUNGTRENUNG(bipy)]. DMF} (1; Himdc=4,5-imidazoledicarboxylate, bipy=4,4'-bipyridine) shows selective gas-storage properties, while the polar nanochannels serve as functional scaffold for the stabilization of highly dispersed Pd nanoparticles. The Pd@MOF1a hybrid is a highly active and recyclable catalyst for the synthesis of propargylamine derivatives through A 3 coupling reactions. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nag A.,International Center for Materials Science | Nag A.,Indian Institute of Science | Raidongia K.,International Center for Materials Science | Hembram K.P.S.S.,International Center for Materials Science | And 4 more authors.
ACS Nano | Year: 2010

Enthused by the fascinating properties of graphene, we have prepared graphene analogues of BN by a chemical method with a control on the number of layers. The method involves the reaction of boric acid with urea, wherein the relative proportions of the two have been varied over a wide range. Synthesis with a high proportion of urea yields a product with a majority of 1-4 layers. The surface area of BN increases progressively with the decreasing number of layers, and the high surface area BN exhibits high CO2 adsorption, but negligible H2 adsorption. Few-layer BN has been solubilized by interaction with Lewis bases. We have used first-principles simulations to determine structure, phonon dispersion, and elastic properties of BN with planar honeycomb lattice-based n-layer forms. We find that the mechanical stability of BN with respect to out-of-plane deformation is quite different from that of graphene, as evident in the dispersion of their flexural modes. BN is softer than graphene and exhibits signatures of long-range ionic interactions in its optical phonons. Finally, structures with different stacking sequences of BN have comparable energies, suggesting relative abundance of slip faults, stacking faults, and structural inhomogeneities in multilayer BN. © 2010 American Chemical Society.

Maitra U.,International Center for Materials Science | Govindaraj A.,International Center for Materials Science | Rao C.N.R.,International Center for Materials Science
Proceedings of the National Academy of Sciences of the United States of America | Year: 2013

Prompted by the early results on the catalytic activity of LiMn2O4 and related oxides in the photochemical oxidation of water, our detailed study of several manganese oxides has shown that trivalency of Mn is an important factor in determining the catalytic activity. Thus, Mn2O3, LaMnO3, and MgMn2O4 are found to be very good catalysts with turnover frequencies of 5 × 10-4 s-1, 4.8 × 10-4 s-1, and 0.8 ×10-4 s-1, respectively. Among the cobalt oxides, Li2Co2O4 and LaCoO3-especially the latter-exhibit excellent catalytic activity, with the turnover frequencies being 9 × 10-4 s-1 and 1.4 × 10-3 s-1, respectively. The common feature among the catalytic Mn and Co oxides is not only that Mn and Co are in the trivalent state, but Co3+ in the Co oxides is in the intermediate t2g 5eg 1 state whereas Mn3+ is in the t2g 3eg 1 state. The presence of the eg 1 electron in these Mn and Co oxides is considered to play a crucial role in the photocatalytic properties of the oxides.

Datta K.K.R.,Jawaharlal Nehru Centre for Advanced Scientific Research | Jagadeesan D.,Jawaharlal Nehru Centre for Advanced Scientific Research | Jagadeesan D.,University of Toronto | Kulkarni C.,Jawaharlal Nehru Centre for Advanced Scientific Research | And 4 more authors.
Angewandte Chemie - International Edition | Year: 2011

A structural chameleon: A porous layered carbon material (PLC) containing nanographene domains was prepared by graphitizing glucose within the nanoscopic voids of an aminoclay template. The size of the pores in the PLC was altered reversibly by a mesoscale order-disorder transformation brought about by an applied mechanical force (see picture). This pore flexibility was exploited for the size-selective separation of dye molecules. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Naidu B.S.,International Center for Materials Science | Gupta U.,International Center for Materials Science | Maitra U.,International Center for Materials Science | Rao C.N.R.,International Center for Materials Science
Chemical Physics Letters | Year: 2014

A study of the visible light induced oxidation of water by perovskite oxides of the formula LaMO3 (M = transition metal) has revealed the best activity with LaCoO3 which contains Co3+ in the intermediate-spin (IS) with one eg electron. Among the rare earth manganites, only orthorhombic manganites with octahedral Mn3+ ions exhibit good catalytic activity, but hexagonal manganites are poor catalysts. Interestingly, not only the perovskite rare earth cobaltites but also solid solutions of Co3+ in cubic rare earth sesquioxides exhibit catalytic activity comparable to LaCoO3, the Co3+ ion in all these oxides also being in the IS t2g5eg1 state. © 2013 Elsevier B.V. All rights reserved.

Rao C.N.R.,International Center for Materials Science
Journal of Physical Chemistry Letters | Year: 2015

Although it is customary to substitute cations in metal oxides, sulfides, and other materials to modify their structure and properties, effects of anion substitution have not been investigated sufficiently. This is particularly true of materials cosubstituted by two anions (such as N3- and F- in place of O2- or P3- and Cl- in place of S2-). Substitution of a trivalent anion along with a monovalent anion helps to eliminate defects, the three anions being isoelectronic and of nearly the same size. Furthermore, such aliovalent anion substitution gives rise to marked changes in the electronic structure and properties. Isovalent anion substitution (e.g., S2- in place of O2- or Se2- in place of S2-) does not bring about such changes. In this Perspective, we examine the electronic structures and properties of several oxides involving cosubstitution of N and F for oxygen. The oxides discussed are TiO2, ZnO, Cr2O3, and BaTiO3. Aliovalent anion substitution decreases the band gaps of the oxides and affect the magnetic and ferroelectric transitions. Sulfides such as CdS and ZnS where sulfur is substituted by P and Cl also show a large decrease in band gaps. Unlike in cation substitution where the conduction band is mainly affected, in the aliovalent anion-substituted materials the p-states of the trivalent anions (N3- and P3-) dominate the top of the valence band, with the metal-trivalent anion (N, P) bond being shorter and the metal-halogen bond longer. Such materials with high visible absorption extending to long wavelengths may indeed find uses. © 2015 American Chemical Society.

Singh G.,Indian Institute of Science | Bajargan G.,Indian Institute of Science | Bajargan G.,Vikram Sarabhai Space Center | Datta R.,International Center for Materials Science | And 3 more authors.
Materials Science and Engineering A | Year: 2014

Plastic deformation and strength of Ti-6Al-4V (Ti64) alloyed with minor additions of B at cryogenic temperatures were investigated through unnotched and notched tensile tests at 20 and 77. K. Marked microstructural refinement that occurs with the trace addition of B to Ti64 was exploited for examining the role of microstructural length scales on the cryogenic plastic deformation. The tensile tests were complemented with detailed microstructural characterisation using transmission electron microscopy and electron back scattered diffraction imaging of the deformed specimens. Experimental results show that the addition of 0.30. wt% and above of B to Ti64 reduces ductility, and in turn enhances the notch sensitivity to the extent that those alloys become unsuitable for low temperature applications. However, the addition of ~0.10. wt% B is beneficial in enhancing the low temperature strength. An examination of the yield strength variation at various temperatures reveals that at 77. K, the colony size determines the yield strength of the alloy, just as it does at room temperature; implying dislocation-mediated plasticity continues to dominate up to 77. K. At 20. K, however, twinning dominates the flow response, with the activation of {112-1} and {56-13-} twinning in addition to {101-2} in the base alloy resulting in enhanced ductility of it as compared to either B-modified alloys at 20. K or the base alloy itself at 77. K. The observation of a reasonable correlation between the lath aspect ratio, given by the colony-to-lath thickness ratios, and yield strength variation at 20. K suggests that coarse colony size in the base alloy allows for the activation of additional twinning mechanisms. © 2014 Elsevier B.V.

Singh G.,Indian Institute of Science | Gaddam R.,Lulea University of Technology | Petley V.,Gas Turbine Research Establishment | Datta R.,International Center for Materials Science | And 4 more authors.
Scripta Materialia | Year: 2013

The strain-controlled fatigue behaviour of Ti-6Al-4V alloy with up to 0.11 wt.% B addition was investigated. Results show significant softening when the strain amplitudes, ΔεT/2, are ≥0.75%. B addition was found to improve the fatigue life for ΔεT/2 ≤ 0.75% as it corresponds to the elastic regime and hence is strength dominated. At ΔεT/2 = 1%, in contrast, the base alloy exhibits higher fatigue life as TiB particle cracking due to strain incompatibility causes easy crack nucleation in the B-modified alloys. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Singh G.,Indian Institute of Science | Satyanarayana D.V.V.,Indian Defence Research And Development Laboratory | Pederson R.,GKN plc | Pederson R.,Lulea University of Technology | And 3 more authors.
Materials Science and Engineering A | Year: 2014

The addition of B, up to about 0.1. wt%, to Ti-6Al-4V (Ti64) reduces its as-cast grain and colony sizes by an order of magnitude. In this paper, the creep resistance of this alloy modified with 0.06 and 0.11. wt% B additions was investigated in the temperature range of 475-550. °C and compared with that of the base alloy. Conventional dead-weight creep tests as well as stress relaxation tests were employed for this purpose. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the alloy with 0.11. wt% B was found to be an order of magnitude lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces - a direct consequence of the microstructural refinement that occurs with the B addition - that provide resistance to dislocation motion. © 2014 Elsevier B.V.

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