The effect of substitution of Al, Ga and Sc ions in the Mn site of LaSrMnO on the thermochemical splitting of CO to generate CO has been studied in detail. Both LaSrMnGaO and LaSrMnScO give high yields of O and generate CO more efficiently than LaSrMnAlO or the parent LaSrMnO. Substitution of even 5% Sc (x = 0.05) results in a remarkable improvement in performance. Thus LaSrMnScO produces 417 μmol g of O and 545 μmol g of CO, respectively, i.e. 2 and 1.7 times more O and CO than LaSrMnO. This manganite also generates H satisfactorily by the thermochemical splitting of HO.

Dey Sunita    Naidu B. S.    C. Rao    

Dalton Transactions

2016

Generation of H and CO by splitting HO and CO respectively constitutes an important aspect of the present-day concerns with energy and environment. The solar thermochemical route making use of metal oxides is a viable means of accomplishing these reduction reactions. The method essentially involves reducing a metal oxide by heating and passing HO or CO over the nonstoichiometric oxide to cause reverse oxidation by abstracting oxygen from HO or CO. While ceria, perovskites and other oxides have been investigated for this purpose, recent studies have demonstrated the superior performance of perovskites of the type LnAMnMO (Ln=rare earth, A=alkaline earth, M=various +2 and +3 metal ions), in the thermochemical generation of H and CO. We present the important results obtained hitherto to point out how the alkaine earth and the Ln ions, specially the radius of the latter, determine the performance of the perovskites. The encouraging results obtained are exemplefied by YSrMnO which releases 483 µmol/g of O at 1673 K and produces 757 µmol/g of CO from CO at 1173 K. The production of H from HO is also quite appreciable. Modification of the B site ion of the perovskite also affects the performance. In addition to perovskites, we present the generation of H based on the MnO/NaMnO cycle briefly.

C. Rao     Dey Sunita   

Journal of Solid State Chemistry

2016

Employing atomic layer deposition, we have grown p-type epitaxial undoped and N-doped anatase TiO(001) thin films on c-axis AlO substrate. From X-ray diffraction and transmission electron microscopy studies, crystallographic relationships between the film and the substrate are found to be (001)//(0001) and [110]//[0110]. N-doping in TiO thin films enhances the hole concentration and mobility. The optical band gap of anatase TiO (3.23 eV) decreases to 3.07 eV upon N-doping. The epitaxial films exhibit room-temperature ferromagnetism and photoresponse. A TiO-based homojunction diode was fabricated with rectification from the p-n junction formed between N-doped p-TiO and n-TiO. (Graph Presented).

Vasu    Sreedhara    Ghatak    C. Rao    

ACS Applied Materials and Interfaces

2016

We report the synthesis, characterization, gas adsorption and hydrogen evolution activity of covalently cross-linked assemblies of MoS and MoS-RGO generated by the Sonogashira coupling reaction. These assemblies show a high surface area and CO storage capacity comparable with some of the high surface area MOFs. MoS assemblies show enhanced hydrogen evolution activity compared to few-layer MoS.

Pramoda    Gupta Uttam    Ahmad Irshad    Kumar Ram    C. Rao    

Journal of Materials Chemistry A

2016

Identification of an appropriate anode material is one of the major challenges for rechargeable Na-ion batteries. Layered MoO is a potential alternative as it can reversibly store large amounts of sodium. However, MoO is a poor electronic conductor and undergoes large volume changes during repeated cycling. Ultrathin nanosheets of 1-3 bilayers of MoO are synthesized starting from the oxidation of few-layer MoS nanosheets. The MoO nanosheets are subsequently chemically tagged with optimum amounts of rGO leading to the formation of a 3D MoO-rGO composite. The MoO-rGO composite exhibits remarkable electrochemical stability, cyclability and high rate capability over a wide range of operating currents (0.05-1 C). This simple and novel material design strategy of MoO-rGO provides the most optimum condition for buffering the volume changes during repeated cycling and provides facile pathways for Na-ion and electron transport in MoO.

Sreedhara    Santhosha A. L.    Bhattacharyya Aninda Jiban    C. Rao    

Journal of Materials Chemistry A

2016

Hydrogen evolution activity of semiconductor heterostructures of the type (TiO)(NiO)/CdZnS has been investigated in detail to examine the role of NiO, used in the place of Pt by making use of nanoparticles and nanotubes of TiO. Combination of NiO and TiO markedly changes the photocatalytic efficiency of the heterostructures. While the H evolution activity increases smoothly with NiO mole farction up to x~0.50, it increases further reaching a maximum at x~0.83, yielding 1.6 mmol h g (AQY ~2.9%) with NaS–NaSO as sacrificial agents, under visible-light irradiation, and 6.84 mmol hg (AQY ~11.7%) and 13.5 mmol h g (AQY ~10%) with benzyl alcohol-acetic acid as sacrificial agents under visible and UV–visible light irradiation respectively. High hydrogen evolution activity to the tune of three times that yielded by equivalent Pt containg heterostructures has been attained, with a NiO mole fraction of 0.83 in the heterostructures.

Roy Anand    Lingampalli    Nassar Ibrahim M.    C. Rao    

Solid State Communications

2016

Substitution of aliovalent N and F anions in place of O in ZnO brings about major changes in the electronic structure and properties, the composition, even with 10 atomic percent or less of the two anions, rendering the material yellow colored with a much smaller band gap. We have examined the variation of band gap of ZnO with progressive substitution of N and F and more importantly prepared ZnNF which is the composition one obtains ultimately upon complete replacement of O ions. In this article, we present the results of a first complete study of the crystal and electronic structures as well as of properties of a stable metal nitride fluoride, ZnNF. This material occurs in two crystal forms, tetragonal and orthorhombic, both with a band gap much smaller than that of ZnO. Electronic structures of ZnNF as well as ZnONF investigated by first-principles calculations show that the valence bands of these are dominated by the N (2p) states lying at the top. Interestingly, the latter is a p-type material, a property that has been anticipated for long time. The calculations predict conduction and valence band edges in ZnNF to be favorable for water splitting. ZnNF does indeed exhibit good visible-light-induced hydrogen evolution activity unlike ZnO. The present study demonstrates how aliovalent anion substitution can be employed for tuning band gaps of materials.

Lingampalli    Manjunath Krishnappa    Shenoy Sandhya    Umesh vasudeo Waghmare    C. Rao    

Journal of the American Chemical Society

2016

Substitution of the sulfide ions in CdS by aliovalent P and Cl ions is known to markedly affect the electronic structure and properties, reducing the band gap of the semiconductor. The decrease in band gap arises because the P (3p) states occupy the top of the valence band while the Cl (3p) orbitals lie deep down in energy. Progressive substitution of S by equal proportions of P and Cl should result in CdPCl or CdPCl. We have investigated the electronic structure of this compound and carried out first-principles calculations to understand the electronic structure and properties. Interestingly, CdPCl is a semiconductor with a band gap of 2.36 eV comparable to that of CdS, and it exhibits a photoluminescence band at 580 nm similar to CdS. Its conduction band and valence band edges are appropriately placed with respect to the water redox potentials, for it to exhibit excellent hydrogen evolution by photochemical water splitting. Visible-light induced hydrogen evolution rate of 1007(±23) and 54(±4) μmol h g has been obtained in the presence and absence of sacrificial agent. Hydrogen evolution in the absence of any sacrificial agent and the absence of photocorrosion seems to be unique features of CdPCl.

Roy Anand    Shenoy U. Sandhya    Manjunath Krishnappa    Vishnoi Pratap    Umesh vasudeo Waghmare    C. Rao    

Journal of Physical Chemistry C

2016

No abstract is available for this article.

Saha Rana    Kalangi Vasu    Negi D. S.    Datta Ranjan    Sundaresan Athinarayanan    C. Rao    

Physica Status Solidi - Rapid Research Letters

2016

The discovery of graphene marks a major event in the physics and chemistry of materials. The amazing properties of this two-dimensional (2D) material have prompted research on other 2D layered materials, of which layered transition metal dichalcogenides (TMDCs) are important members. Single-layer and few-layer TMDCs have been synthesized and characterized. They possess a wide range of properties many of which have not been known hitherto. A typical example of such materials is MoS2. In this article, we briefly present various aspects of layered analogues of graphene as exemplified by TMDCs. The discussion includes not only synthesis and characterization, but also various properties and phenomena exhibited by the TMDCs. This article is part of the themed issue Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene.

Jana Manoj K.    C. Rao    

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

2016