The nanocomposites of MoS nanosheets with the metal-organic framework, ZIF-8, have been synthesized starting with the layers of 1T-MoS generated by Li intercalation of bulk MoS, followed by exfoliation. The nanocomposites contain the Zn-S bond and exhibit reasonably high surface areas. They exhibit CO uptake higher than ZIF-8. Heating the nanocomposites to 900 °C under a N atmosphere yields MoS-ZnS nanocomposites which show good activity for the visible-light induced hydrogen evolution reaction.

Pramoda    Kaur Manjodh    Gupta Uttam    C. Rao    

Dalton Transactions

2016

In this report, a systematic study of the effects of p- and n-type doping of the inorganic fullerene (IF) MoS on the efficiency of the hydrogen evolution reaction (HER) is described. Active edge site enriched IF-MoS, promoted by strategically introducing Nb (p-type) and Re (n-type) dopants (below 500 ppm), enables facile HER over a range of pH values. Experimental results suggest that although Nb-doping on IF-MoS leads to better electrocatalytic HER activity in an alkaline medium with an onset potential difference of 80 mV, Re-doping gives excellent activity in an acidic medium. The present work presents a systematic study of HER activity by finely tuning the activity in different electrolyte media with varied pH values through deliberate doping of the parent catalyst with p- and n- type materials. The doped IF-MoS catalysts exhibit excellent catalytic activity even with sea water as an electrolyte.

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

ChemElectroChem

2016

The compelling need for safe storage and transportation of H has made liquid-phase materials safer H-carriers with a high gravimetric and volumetric hydrogen density. Unlike thermal or electrocatalytic decomposition on precious metal catalysts, a photocatalytic route to decomposing these liquid-phase materials can offer triggered onboard production of H and help mitigate the safety issues concerned with H storage. We have investigated visible-light induced H evolution from aqueous hydrazine using CdS quantum dots (QDs) as metal-free photocatalysts. Hydrazine acts as a H carrier as well as a donor, giving rise to a visible-light induced H evolution activity as high as 33 mmol h g at pH 8. This has been achieved by the use of CdS QDs capped with S ligands. The use of larger ligands such as mercaptopropionic acid hinders the adsorption of hydrazine onto CdS QDs and significantly decreases the activity. The effect of pH on the hydrogen yield in aqueous hydrazine has also been examined.

Jana Manoj K.    Gupta Uttam    C. Rao    

Dalton Transactions

2016

We present experimental measurements and first-principles theoretical analysis of high-temperature electron-transport properties of polycrystalline Te-deficient 2H- and 1T′-MoTe. Electron transport measurements in the temperature range 300–673 K show that polycrystalline 2H-MoTe exhibits two regimes of activated conduction: hopping of defect-induced localized carriers at lower temperatures and an extended state conduction at higher temperatures. Its Seebeck coefficient changes from p-type to n-type around 497 K peaking near 370 K, which is ascribed to mixed conduction of carriers. In contrast, 1T′-MoTe exhibits metallic conduction up to 300 K beyond which conductivity slightly increases due to thermal excitation of the minority carriers. 2H- and 1T′ forms of MoTe exhibit thermal conductivity with opposite temperature-dependence due to dominant electronic thermal conductivity in the latter. Using first-principles calculations based on density functional theory, we determine the nature of defect states associated with Te-vacancies in 2H-, 1T′- and Td-MoTe. The defect bands associated with Te vacancies appear within the gap of 2H-MoTe and in the pseudo gap of 1T′-MoTe, thereby reducing the bandgap of the former and making the latter more metallic. These defect states are crucial to understanding the observed trends in the temperature-dependent transport properties of Te-deficient 2H- and 1T′-MoTe.

Jana Manoj K.    Singh Anjali    Sampath Archana    C. Rao     Umesh vasudeo Waghmare   

Zeitschrift fur Anorganische und Allgemeine Chemie

2016

The recent discovery of non-saturating giant positive magnetoresistance has aroused much interest in Td-WTe2. We have investigated structural, electronic and vibrational properties of bulk and few-layer Td-WTe2 experimentally and theoretically. Spin-orbit coupling is found to govern the semi-metallic character of Td-WTe2 and its structural link with the metallic 1 T form provides an understanding of its structural stability. There is a metal-to-insulator switch-over in the electrical conductivity and a change in the sign of the Seebeck coefficient around 373 K. Lattice vibrations of Td-WTe2 have been analyzed using first-principles calculations. Out of the 33 possible zone-center Raman active modes, five distinct Raman bands are observed around 112, 118, 134, 165 and 212 cm^-1 in bulk Td-WTe2. Based on symmetry analysis and calculated Raman tensors, we assign the intense bands at 165 cm^-1 and 212 cm^-1 to the and modes, respectively. Most of the Raman bands stiffen with decreasing thickness, and the ratio of the integrated intensities of the to bands decreases in the few-layer sample, while all the bands soften in both the bulk and few-layer samples with increasing temperature.

Jana Manoj K.    Singh Anjali    Dattatray Late    Catherine Rajamathi    Biswas Kanishka    Claudia Felser    Umesh vasudeo Waghmare    C. Rao    

Journal of Physics Condensed Matter

2015

Performance of supercapacitors based on 1:1 (by weight) composites of polyaniline (PANI) with nanosheets of nitrogenated reduced graphene oxide (NRGO), BCN, MoS and WS has been investigated in detail. The highest specific capacitance is found with the 1:1 NRGO-PANI composite, the value being 561F/g at a current density of 0.2A/g. All the 1:1 nanocomposites show good cyclability. Increasing the PANI content increases the specific capacitance and the highest value found being 715F/g at a current density of 0.5A/g in the case of the 1:6 NRGO-PANI composite. However, all the 1:6 composites show a marked decrease in specific capacitance with increase in current density. The energy density of 1:6 NRGO-PANI is ~25Wh/Kg at 0.5A/g and 1:1 NRGO-PANI is ~19Wh/Kg at 0.2A/g. NRGO-PANI composites clearly stand out as viable materials for practical applications.

Gopalakrishnan K.    Sultan S.    Achutharao Govindaraj    C. Rao    

Nano Energy

2015

(ZnS)0.4(AgInS2)0.6 nanocrystals (NCs) capped by S^2- ions exhibit interesting electronic properties, absorbing visible light along with a suitable band alignment as well as properties such as high surface area providing active reaction sites for photocatalytic H2 evolution. A high activity of 5.0 mmol g^-1 h^-1 is achieved using non-toxic (ZnS)0.4(AgInS2)0.6 NCs as photocatalysts without the need for a noble metal co-catalyst.

Jagadeeswararao Metikoti    Dey Sunita    Angshuman Nag    C. Rao    

Journal of Materials Chemistry A

2015

Perovskite oxides of the Ln0.5A0.5MnO3 (Ln=lanthanide, A=Sr, Ca) family have been investigated for the thermochemical splitting of H2O and CO2 to produce H2 and CO respectively. The amounts of O2 and CO produced strongly depend on the size of the rare earth ions and alkaline earth ions. The manganite with the smallest rare earth possessing the highest distortion and size disorder as well as the smallest tolerance factor, gives out the maximum amount of O2, and, hence, the maximum amount of CO. Thus, the best results are found with Y0.5Sr0.5MnO3, which possesses the highest distortion and size disorder. Y0.5Sr0.5MnO3 shows remarkable fuel production activity even at the reduction and oxidation temperatures as low as 1200 °C and 900 °C, respectively.

Dey Sunita    Naidu B. S.    C. Rao    

Chemistry - A European Journal

2015

Novel properties of graphene have been well documented, whereas the importance of nanosheets of MoS2 and other chalcogenides is increasingly being recognized over the last two to three years. Borocarbonitrides, BxCyNz, with insulating BN and conducting graphene on either side are new materials whose properties have been attracting attention. These two-dimensional (2D) materials contain certain common features. Thus, graphene, MoS2, and borocarbonitrides have all been used in supercapacitor applications, oxygen reduction reactions (ORRs), and lithium-ion batteries. It is instructive, therefore, to make a comparative study of some of the important properties of these layered materials. In this article, we discuss properties related to energy devices at length. We examine the hydrogen evolution reaction facilitated by graphene, MoS2, and related materials. We also discuss gas and radiation sensors based on graphene and MoS2 as well as gas storage properties of graphene and borocarbonitrides. The article should be useful in making a judicious choice of which 2D material to use for a particular application.

C. Rao     Gopalakrishnan K.    Maitra Urmimala   

ACS Applied Materials and Interfaces

2015

We report high-pressure Raman-scattering studies on single-crystal ReO3 up to 26.9 GPa at room temperature, complemented by first-principles density functional calculations to assign the modes and to develop understanding of the subtle features of the low-pressure phase transition. The pressure (P) dependence of phonon frequencies (ω) reveals three phase transitions at 0.6, 3, and 12.5 GPa with characteristic splitting and changes in the slope of ω(P). Our first-principles theoretical analysis confirms the role of the rotational modes of ReO6,M3, to the lowest pressure structural transition, and shows that the transition from the Pm3m to the Im3 structure is a weak first-order transition, originating from the strong anharmonic coupling of the M3 modes with the acoustic modes (strain).

Muthu    Teredesai Pallavi    Saha Surajit    Suchitra    Umesh vasudeo Waghmare    Ajay kumar Sood    C. Rao    

Physical Review B - Condensed Matter and Materials Physics

2015