A MoS2-RGO composite and borocarbonitride (BC5N) have been used as electrodes to selectively detect dopamine and uric acid in the presence of ascorbic acid. Both the electrodes show excellent eletrocatalytic activity towards the detection of dopamine, the detection limits being 0.55μM and 2.1μM in the case of MoS2-RGO and BCN respectively. MoS2-RGO shows a linear range of current over the 1-110μM concentrations of dopamine, while BCN shows over the 2.3-20μM range. BCN also exhibits satisfactory performance in the oxidation of uric acid with a detection limit of 3.8μM and the linear range from 4 to 40μM. The MoS2-RGO has also been used to detect adenine as well.

Pramoda    Moses Kota    Maitra Urmimala    C. Rao    

Electroanalysis

2015

The preparation of 1D WS2 and MoS2 flexible nanoribbons by laser-induced unzipping of the nanotubes is reported. The nanoribbons are of high quality, uniform width, and devoid of surface contamination. The zig-zag edges in WS2 nanoribbons give rise to ferromagnetism at room temperature.

Vasu    Sharma Yamijala    Ali Khorsand Zak    Gopalakrishnan K.    Swapan Kumar Pati    C. Rao    

Small

2015

Hydrogen can be generated by visible light irradiation of semiconductor heterostructures of the type ZnO/Pt/CdS and TiO2/Pt/CdS. In order to understand the dependence of hydrogen generation on the properties of the nanoparticles of ZnO and TiO2, we have carried out systematic studies. For this purpose, we have studied photocatalytic hydrogen generation by ZnO(TiO2)/Cd1 - xZnxS and ZnO(TiO2)/Pt/Cd1 - xZnxS (x = 0.0, 0.2) heterostructures with oxide nanostructures possessing different morphologies and surface areas. In the case of TiO2/Pt/Cd0.8Zn0.2S heterostructures, the highest H2 evolution rate up to1.76 mmol h^-1 g^-1 were obtained with H2Ti3O7 nanotubes, with the least H2 evolution rate (0.55 mmol h^-1 g^-1) from TiO2 powder (Degussa P25). In the case of ZnO/Pt/CdS heterostructures, the highest H2 evolution rate (6.88 mmol h^-1 g^-1) were obtained from ZnO nanorods1, whereas the least H2 evolution rate (2.55 mmol h^-1 g^-1) was obtained from ZnO nanorods3. The photocatalytic activity of heterostructures generally follows the trend in BET surface areas of the oxide nanostructures, with high surface area favoring good hydrogen evolution activity.

Roy Anand    Lingampalli    Saha Sujoy    C. Rao    

Chemical Physics Letters

2015

The effect of N-doping on the paramagnetic-antiferromagnetic transition associated with the metal-insulator (M-I) transition of V2O3 at 150 K has been studied in bulk samples as well as in nanosheets. The magnetic transition temperature of V2O3 is lowered to 120 K in the N-doped samples. Electrical resistivity data also indicate a similar lowering of the M-I transition temperature. First-principles DFT calculations reveal that anionic (N) substitution and the accompanying oxygen vacancies reduce the energy of the higherature metallic corundum phase relative to the monoclinic one leading to the observed reduction in Nèel temperature. In the electronic structure of N-substituted V2O3, a sub-band of 2p states of trivalent anion (N) associated with its strong bond with the vanadium cation appears at the top of the band of O(2p) states, the 3d-states of V being slightly higher in energy. Its band gap is thus due to crystal field splitting of the degenerate d-orbitals of vanadium and superexchange interaction, which reduces notably (ΔEg=-0.4 eV) due to their hybridization with the 2p states of nitrogen. A weak magnetic moment arises in the monoclinic phase of N-substituted V2O3 with O-vacancies, with a moment of -1 μB/N localized on vanadium atoms in the vicinity of oxygen vacancies.

Kumar Nitesh    Sreedhara    Kouser Summayya    Umesh vasudeo Waghmare    C. Rao    

ChemPhysChem

2015

Electrochemical generation of hydrogen by non-precious metal electrocatalysts at a lower overpotential is a focus area of research directed towards sustainable energy. The exorbitant costs associated with Pt-based catalysts is the major bottleneck associated with commercial-scale hydrogen generation. Strategies for the synthesis of cost-effective and stable catalysts are thus key for a prospective 'hydrogen economy'. In this report, we highlight a novel and general strategy to enhance the electrochemical activity of molybdenum disulfide (MoS2) in a fullerene structure (IF-). In particular, pristine (undoped) and rhenium-doped nanoparticles of MoS2 with fullerene-like structures (IF-MoS2) were studied, and their performance as catalysts for the hydrogen evolution reaction (HER) was compared to that of 2H-MoS2 particles (platelets). The current density of the IF-MoS2 was higher by one order of magnitude than that of few-layer (FL-) MoS2, due to the enhanced density of the edge sites. Furthermore, Re doping of as low as 100 ppm in IF-MoS2 decreased the onset potential by 60-80 mV and increased the activity by 60 times compared with that of the FL-MoS2. The combined synergistic effect of Re doping and the IF structure not only changes the intrinsic nature of the MoS2 but also increases its reactivity. This strategy highlights the potential use of the IF structure and Re doping in electrocatalytic hydrogen evolution using MoS2-based catalysts.

Chhetri Manjeet    Gupta Uttam    Lena Yadgarov    Rital Rosentsveig    Reshef Tenne    C. Rao    

Dalton Transactions

2015

Using first-principles local and hybrid density functional theoretical calculations, a thickness-dependent electronic structure of layered GaS is determined, and it is shown that 2D GaS has an electronic structure with valence and conduction bands that straddle the redox potentials of hydrogen evolution reaction and oxygen evolution reaction up to a critical thickness (<5.5 nm). Here, simulations of adsorption of H2O on nanoscale GaS reveal that localized electronic states at its edges appear in the gap and strengthen the interaction with H2O, further activating the surface atomic sites. It is thus predicted that GaS synthesized with a controlled thickness and preferred edges may be an efficient catalyst for photocatalytic splitting of water. Experiments that verify some of the predictions in this study are presented, and it is shown that GaS is effective in absorption of light and evolution of H2 (887 μmol h^-1 g^-1) in the presence of aqueous solution of hydrazine (1% v/v). This study should open up the use of nanoscale GaS in conversion of solar energy into environment-friendly chemical energy in the form of hydrogen. Using first-principles calculations, it is shown that 2D-GaS (thickness < 5.5 nm) possesses an electronic structure with valence and conduction bands that straddle the redox potentials of hydrogen evolution and oxygen evolution reactions, which is ideal for efficient photocatalysis for overall water splitting in the presence of visible light.

Kouser Summayya    Thannikoth Anagha    Gupta Uttam    Umesh vasudeo Waghmare    C. Rao    

Small

2015

Perovskite oxides of the composition LaCaMnO (LCM) have been investigated for the thermochemical splitting of HO and CO to produce H and CO, respectively. The study was carried out in comparison with LaxSrMnO, CeO and other oxides. The LCM system exhibits superior characteristics in high-temperature evolution of oxygen, and in reducing CO to CO and HO to H. The best results were obtained with LaCaMnO whose performance is noteworthy compared to that of other oxides including ceria. The orthorhombic structure of LCM seems to be a crucial factor.

Dey Sunita    Naidu B. S.    Achutharao Govindaraj    C. Rao    

Physical Chemistry Chemical Physics

2015

First-principles density functional calculations were carried out to determine the structure as well as electronic and magnetic properties of N and F co-substituted CrO. The formation of strong Cr-N bonds upon substitution of oxygen with nitrogen leads to large distortions in the local structure and changes in magnetic moments, which are partly compensated by co-substitution with fluorine. The effects of spin-orbit coupling are relatively weak, but its combination with local structural distortions gives rise to canting of spins and an overall magnetic moment in N, F co-substituted CrO. Experimentally, we observe spin canting in N, F co-substituted CrO with considerable enhancement in the coercive field at low temperatures. Don′t be DFT: Spin-orbit coupling along with local structural distortion gives rise to strong spin canting in N, F co-substituted CrO.

Pan Jaysree    Umesh vasudeo Waghmare    Kumar Nitesh    Ehi-Eromosele C. O.    C. Rao    

ChemPhysChem

2015

Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first-principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub-band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co-substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well.

Kouser Summayya    Lingampalli    Chithaiah P.    Roy Anand    Saha Sujoy    Umesh vasudeo Waghmare    C. Rao    

Angewandte Chemie - International Edition

2015

First-principles density functional calculations were carried out to determine the structure as well as electronic and magnetic properties of N and F co-substituted CrO. The formation of strong Cr-N bonds upon substitution of oxygen with nitrogen leads to large distortions in the local structure and changes in magnetic moments, which are partly compensated by co-substitution with fluorine. The effects of spin-orbit coupling are relatively weak, but its combination with local structural distortions gives rise to canting of spins and an overall magnetic moment in N, F co-substituted CrO. Experimentally, we observe spin canting in N, F co-substituted CrO with considerable enhancement in the coercive field at low temperatures.

Pan Jaysree    Umesh vasudeo Waghmare    Kumar Nitesh    Ehi-Eromosele    C. Rao    

ChemPhysChem

2015