Few-layer graphene can be chlorinated up to 56 wt.% by irradiation with UV light in a liquid chlorine medium. The chlorinated sample decomposes on heating or on laser irradiation releasing all the chlorine. Similar results have been obtained with the bromination of few-layer graphene.

K. Gopalakrishnan;K. S. Subrahmanyam;Prashant Kumar;A. Govindaraj;C. Rao

RSC Advances

2012-2-21

Two layered tin(II) oxalate structures have been prepared by hydrothermal methods in the presence of structure-directing organic amines. The crystal data for these structures are as follows: oxalate I, [(CH₃)₂NH(CH₂)₂NH(CH ₃)₂]²⁺[Sn₂(C₂O ₄)₃]^2-·H₂O, monoclinic, space group C2/c (no. 15), a = 16.567 (8) Å, b = 10.851 (6) Å, c = 11.652 (6) Å, β = 102.62 (3)°, V = 2039.0 (1) ų, Z = 4, M = 637.4(1), D_calc = 2.825 g cm^-3, Mo Kα, R_F = 0.04; oxalate II, [C(NH₂)₃]₂⁺[Sn₄(C ₂O₄)₅]^2-·2H₂O, orthorhombic, space group Pbca (no. 61), a = 11.390 (1) Å, b = 14.742 (1) Å, c = 16.755 (1) Å, V = 2813.1 (1) ų, Z = 8, M = 1070.8(1), D_calc = 2.844 g cm^-3, Mo Kα, R_F = 0.06. In I, pseudo-pentagonal-bipyramidal SnO₆ units form a puckered layered structure by sharing oxygens with the oxalate anions. The layers contain 8- and 12-membered apertures, and the amine (protonated N,N,N′N′-tetramethyl-1,2-diaminoethane) and water molecules are in the interlamellar region where they interact with the framework and with each other by hydrogen bonding. The lone pairs of the Sn(II) atoms point into the interlamellar region. Oxalate II contains both square-pyramidal SnO₄ units and SnO₆ units similar to those in I. These units together form a saw-tooth lamellar structure by linking through the oxalates. The sheets contain 20-membered corrugated rings, which hold two amine cations (guanidinium) and two water molecules, which interact with the framework via hydrogen bonding.

Srinivasan Natarajan;R. Vaidhyanathan;C. Rao;S. Ayyappan;Anthony K. Cheetham

Chemistry of Materials

1999

Results of a detailed investigation of the structure and electron-transport properties of (Formula presented)(Formula presented)(Formula presented) (A=Ca, Sr) over a wide range of compositions are presented along with those of parent (Formula presented) containing different percentages of (Formula presented). The electrical resistivity (ρ) and magnetoresistance (MR) of polycrystalline pellets have been measured in the 4.2-400 K range in magnetic fields up to 6 T and the Seebeck coefficient (S) from 100 to 400 K. The electrical measurements were supplemented by ac susceptibility and magnetization measurements. MR is large and negative over a substantial range of compositions and peaks around temperatures close to the ferromagnetic transition temperatures ((Formula presented)). An insulator to metal-like transition occurs near the (Formula presented) and the temperature dependence of ρ below (Formula presented) is related to the magnetization although ρ in the metallic state is generally much larger than the Mott’s maximum metallic resistivity. The occurrence of giant magnetoresistance is linked to the presence of an optimal proportion of (Formula presented) ions and is found in the rhombohedral and the cubic structures where the Mn-O distance is less than 1.97 Å and the Mn-O-Mn angle is 170°±10°. The field dependence of MR shows the presence of two distinct regimes. The thermopower S shows a positive peak in the composition range at a temperature where MR also peaks; S becomes more negative with increase in (Formula presented).

R. Mahendiran;S. Tiwary;A. Raychaudhuri;T. Ramakrishnan;R. Mahesh;N. Rangavittal;C. Rao

Physical Review B - Condensed Matter and Materials Physics

1996

Effect of ruthenium and nickel on the reduction behavior of Fe³⁺ Al₂O₃ to give the Fe1bAl₂O₃ metal-ceramic composite has been studied by employing x-ray diffraction. ⁵⁷Fe Mössbauer spectroscopy and electron microscopy. Both ruthenium and nickel promote the hydrogen reduction of Fe³⁺, giving nearly total reduction to the metallic phase at 1220K. Besides metallic iron in the ferromagnetic α-form, paramagnetic alloys of Fe with Ru and Ni are formed during the reduction.

M. Verelst;K. R. Kannan;G. N. Subbanna;C. Rao;M. Brieu;A. Rousset

Materials Research Bulletin

1993-4

Two isostructural, organically-templated, 2D coordination polymers, one containing Ni^II and another containing Co^II and Ni ^II ions with the general formulae, {[EDAH₂][M ₁M₂F₂(SO₄)₂(H ₂O)₂]}_n, (EDA = ethylenediamine, M₁ = M₂ = Ni^II (1), and M₁ = Co^II, M₂ = Ni^II (2)) have been synthesized and structurally characterized. 1 and 2 consist of a 1D chain bridged by F^- ion, [M-F-M]_n which is interconnected by SO₄^2- tetrahedra forming a 2D [Ni₂F₂(SO₄) ₂(H₂O)₂]_n^2- or [CoNiF₂(SO₄)₂(H₂O)₂] _n^2- corrugated sheet which are templated by diprotonated ethylenediamine [EDAH₂] cation. Temperature-dependent magnetic measurements reveal the presence of spin-canted antiferromagnetism in both 1 and 2. 1 behaves like a soft magnet with a small magnetic hysteresis with a coercive field (H_c) of 0.46 kOe and a remnant magnetization (M _R) of 0.09 μ_B. 2, on the other hand exhibits relatively a hard magnet like behavior with large magnetic hysteresis with H_c = 8.74 kOe and M_R = 0.76 μ_B. The difference in magnetic behaviors of 1 and 2 is attributed to the difference in single-ion magnetic anisotropy and spin magnitudes of Ni^II (S = 1) and Co^II (S = 3/2) ions.

C. M. Nagaraja;Tapas Kumar Maji;C. Rao

Inorganica Chimica Acta

2012-7-1

The covalent functionalization of transition metal dichalcogenides (TMDs) has attracted significant interest because of their novel physicochemical properties for various applications. Herein, we report on amino acid (AA)-induced solution-processed simultaneous exfoliation and in situ covalent functionalization of exfoliated molybdenum disulfide (MoS₂). Covalent functionalization of MoS₂ with AAs was experimentally validated by various spectrochemical characterization and density functional theory calculations. We find that N terminal binding (NH₂) of AAs with sulfur defects on exfoliated MoS₂ is much more favorable than the C terminal binding (COOH). Notably, the MoS₂ flakes have significantly improved biocompatibility with normal intestinal epithelial cell-6. This exfoliation technique is presented here as general strategy; it is not limited to MoS₂ and may apply to exfoliating other MX₂ compounds of TMDs.

Elumalai Satheeshkumar;Arkamita Bandyopadhyay;M. B. Sreedhara;Swapan K. Pati;C. Rao;Masahiro Yoshimura

ChemNanoMat

2017

A three-dimensional open-framework cadmium oxalate, K[C₃N₂H₅] [Cd(C₂O₄)₂], in which both the amine and the K⁺ ion participate in the formation of the structure, has been synthesized and characterized for the first time.

P. A. Prasad;S. Neeraj;Srinivasan Natarajan;C. Rao

Chemical Communications

2000-7-21

We have measured near normal incidence far-infrared (FIR) reflectivity spec- tra of a single crystal of TbMnO₃ from 10 K to 300 K in the spectral range of 50 cm^-1-700 cm^-1. Fifteen transverse optic (TO) and longitudinal optic (LO) modes are identified in the imaginary part of the dielectric function ε₂(ω) and energy loss function Im(-1/ε(ω)), respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature T _N (̃46 K). We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the superexchange integral be- tween the Mn³⁺ spins. The effective charge of oxygen (ZO) calculated using the measured LO{TO splitting increases below T_N.

Pradeep Kumar;Surajit Saha;C. R. Serrao;A. K. Sood;C. Rao

Pramana - Journal of Physics

2010-2

Sensing characteristics of ZnO, In₂O₃ and WO ₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5-15 nm diameter, prepared by the solvothermal process show a sensitivity of 20-25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases.

C. S. Rout;K. Ganesh;A. Govindaraj;C. Rao

Applied Physics A: Materials Science and Processing

2006-11

Layer-dependent electronic structure and properties of gallium monochalcogenides, GaX where X = S, Se, Te, have been investigated using first-principles calculations based on various functionals, with a motivation to assess their use in photocatalytic water splitting. Since hydrogen evolution by water splitting using visible light provides a promising way for solar energy conversion, both theoretical and experimental studies have been carried out on the photochemical hydrogen evolution by GaTe. We also present the Raman spectra of GaTe examined by both theory and experiment.

U. Sandhya Shenoy;Uttam Gupta;Deepa S. Narang;Dattatray J. Late;Umesh V. Waghmare;C. Rao

Chemical Physics Letters

2016-5