Research Papers (Prof. C.N.R. Rao)

Composition-dependent photoluminescence and electronic structure of 2-dimensional borocarbonitrides, BCXN (x=1, 5)

2017-02-21T10:24:16Z

Composition-dependent photoluminescence and electronic structure of 2-dimensional borocarbonitrides, BCXN (x=1, 5) Moses, Kota; Shirodkar, Sharmila N.; Waghmare, Umesh V.; Rao, C. N. R. Layered borocarbonitrides BCN and BC5N with a wide difference in composition have been prepared by the urea route. These 2D materials show a significant difference in the photoluminescence spectra, with BCN and BC5N showing maxima at 340 and 410 nm (3.61 and 3.0 eV), besides exhibiting different electrical resistivities. First-principles calculations show that BCN and BC5N are associated with different band gaps, the gap of the carbon-rich composition being lower. The change in the electronic structure and properties is related to the composition of BCXN i.e. the ordering of the graphene and BN domains. Restricted Access

Porous graphene frameworks pillared by organic linkers with tunable surface area and gas storage properties

2017-02-21T10:24:55Z

Porous graphene frameworks pillared by organic linkers with tunable surface area and gas storage properties Kumar, Ram; Suresh, Venkata M.; Maji, Tapas Kumar; Rao, C. N. R. We report the design and synthesis of two porous graphene frameworks (PGFs) prepared via covalent functionalization of reduced graphene oxide (RGO) with iodobenzene followed by a C-C coupling reaction. In contrast to RGO, these 3D frameworks show high surface area (BET, 825 m(2) g(-1)) and pore volumes due to the effect of pillaring. Interestingly, both the frameworks show high CO2 uptake (112 wt% for PGF-1 and 60 wt% for PGF-2 at 195 K up to 1 atm). PGFs show nearly 1.2 wt% H-2 storage capacity at 77 K and 1 atm, increasing to similar to 1.9 wt% at high pressure. These all carbon-based porous solids based on pillared graphene frameworks suggest the possibility of designing related several such novel materials with attractive properties. Restricted Access

Synthesis, anion order and magnetic properties of RVO3-xNx perovskites (R = La, Pr, Nd; 0 <= x <= 1)

2017-02-21T10:24:47Z

Synthesis, anion order and magnetic properties of RVO3-xNx perovskites (R = La, Pr, Nd; 0 <= x <= 1) Oro-Sole, Judith; Clark, Lucy; Kumar, Nitesh; Bonin, William; Sundaresan, A.; Attfield, J. Paul; Rao, C. N. R.; Fuertes, Amparo The rare earth vanadium oxynitride perovskites RVO3-xNx (R = La, Pr, Nd; 0 <= x <= 1) have been prepared by treatment of RVO4 precursors in NH3. The ammonolysis reactions proceed through an initial reduction of RVO4 precursors to RVO3 perovskites that are progressively nitrided and reoxidised to RVO3-xNx materials with varying proportions of V4+/V3+. Variable temperature neutron diffraction studies show that NdVO2N and PrVO2.24N0.76 have orthorhombic Pbnm symmetry between 3.5 and 300 K, but LaVO2.11N0.89 undergoes a broad Pbnm to R3c structural transition over this temperature range. In LaVO3-xNx samples the proportion of the R (3) over barc phase at room temperature increases with the nitrogen content. The partial anion order indicative of planes of cis-VN2 chains found in NdVO2N is also present in PrVO2.24N0.76, and is thus robust to the disorder created by non-stoichiometry. Magnetic measurements reveal spin freezing transitions at low temperatures in LaVO2.09N0.91 and PrVO2.24N0.76, but NdVO2N is paramagnetic. Restricted Access

Few-Layer Borocarbonitride Nanosheets: Platinum-Free Catalyst for the Oxygen Reduction Reaction

2017-02-21T10:24:02Z

Few-Layer Borocarbonitride Nanosheets: Platinum-Free Catalyst for the Oxygen Reduction Reaction Moses, Kota; Kiran, Vankayala; Sampath, S.; Rao, C. N. R. The present study demonstrates the use of few-layer borocarbonitride nanosheets synthesized by a simple method as non-platinum cathode catalysts for the oxygen reduction reaction (ORR) in alkaline medium. Composition-dependent ORR activity is observed and the best performance was found when the composition was carbon-rich. Mechanistic aspects reveal that ORR follows the 4e(-) pathway with kinetic parameters comparable to those of the commercial Pt/C catalyst. Excellent methanol tolerance is observed with the BCN nanosheets unlike with Pt/C. Restricted Access