Chandra Sekhar Rout

Supercapacitor Electrodes Based on Layered Tungsten Disulfide-Reduced Graphene Oxide Hybrids Synthesized by a Facile Hydrothermal Method

We report here the synthesis of layer structured WS2/reduced graphene oxide (RGO) hybrids by a facile hydrothermal method for its possible application as supercapacitor materials in energy storage devices. The prepared two-dimensional materials are characterized thoroughly by various analytical techniques to ascertain their structure and to confirm the absence of any impurities. Two-electrode capacitance measurements have been carried out in aqueous 1 M Na2SO4. The WS2/RGO hybrids exhibited enhanced supercapacitor performance with specific capacitance of 350 F/g at a scan rate of 2 mV/s. The obtained capacitance values of WS2/RGO hybrids are about 5 and 2.5 times higher than bare WS2 and RGO sheets. Because of the unique microstructure with combination of two layered materials, WS2/RGO hybrids emerge as a promising supercapacitor electrode material with high specific capacitance, energy density, and excellent cycling stability.

Effects of charge transfer interaction of graphene with electron donor and acceptor molecules examined using Raman spectroscopy and cognate techniques

The effects of the interaction of few-layer graphene with electron donor and acceptor molecules have been investigated by employing Raman spectroscopy, and the results compared with those from electrochemical doping. The G-band softens progressively with increasing concentration of tetrathiafulvalene (TTF) which is an electron donor, while the band stiffens with increasing concentration of tetracyanoethylene (TCNE) which is an electron acceptor. Interaction with both TTF and TCNE broadens the G-band. Hole and electron doping by electrochemical means, however, stiffen and sharpen the G-band. The 2D-band position is also affected by interaction with TTF and TCNE. More importantly, the intensity of the 2D-band decreases markedly with the concentration of either. The ratio of intensities of the 2D-band and G-band decreases with an increase in TTF or TCNE concentration, and provides a means for carrier titration in the charge transfer system. Unlike the intensity of the 2D-band, that of the D-band increases on interaction with TTF or TCNE. All of these effects occur due to molecular charge transfer, also evidenced by the occurrence of charge transfer bands in the electronic absorption spectra. The electrical resistivity of graphene varies in opposite directions on interaction with TTF and TCNE, the resistivity depending on the concentration of either compound.

Graphene-based hybrid materials and devices for biosensing.

Graphenes unique properties have made it a popular candidate for nanomaterial based biosensors. Its remarkable characteristics have led to its rapid development in the electrochemical biosensing, field effect transistors, and optical biosensing as well as the creation graphene-metal nanoparticle hybrids for improved performance. This article comprehensively reviews the most recent trends in graphene-based biosensors and attempts to identify the future directions in which the field is likely to thrive.

Synthesis and Characterization of Patronite Form of Vanadium Sulfide on Graphitic Layer

With the exploding interest in transition metal chalcogenides, sulfide minerals containing the dianion S2(2-), such as pyrite (FeS2), cattierite (CoS2), and vaesite (NiS2), have recently attracted much attention for potential applications in energy conversion and storage devices. However, the synthesis of the patronite structure (VS4, V(4+)(S2(2-))2) and its applications have not yet been clearly demonstrated because of experimental difficulties and the existence of nonstoichiometric phases. Herein, we report the synthesis of VS4 using a simple, facile hydrothermal method with a graphene oxide (GO) template and the characterization of the resulting material. Tests of various templates such as CNT, pyrene, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and graphite led us to the conclusion that the graphitic layer plays a role in the nucleation during growth of VS4. Furthermore, the VS4/rGO hybrid was proved to be a promising functional material in energy storage devices.

Superior Field Emission Properties of Layered WS2-RGO Nanocomposites

We report here the field emission studies of a layered WS2-RGO composite at the base pressure of ~1 × 10−8 mbar. The turn on field required to draw a field emission current density of 1 μA/cm2 is found to be 3.5, 2.3 and 2 V/μm for WS2, RGO and the WS2-RGO composite respectively. The enhanced field emission behavior observed for the WS2-RGO nanocomposite is attributed to a high field enhancement factor of 2978, which is associated with the surface protrusions of the single-to-few layer thick sheets of the nanocomposite. The highest current density of ~800 μA/cm2 is drawn at an applied field of 4.1 V/μm from a few layers of the WS2-RGO nanocomposite. Furthermore, first-principles density functional calculations suggest that the enhanced field emission may also be due to an overalp of the electronic structures of WS2 and RGO, where graphene-like states are dumped in the region of the WS2 fundamental gap.

Temperature dependent Raman spectroscopy of chemically derived few layer MoS2 and WS2 nanosheets

We have systematically investigated the temperature dependent Raman spectroscopy behavior of a few layered MoS2 and WS2 nanosheets synthesized using simple hydrothermal method. Our result reveals A1g and E12g modes soften as temperature increases from 77 K to 623 K. This behavior can be explained in terms of a double resonance process which is active in single- and few layer thick nanosheets. The frequency shifts and peak broadening can provide unambiguous, nondestructive, and accurate information of a few layered MoS2 and WS2. This mechanism can also be applicable in characterizing the structural, optical, electronic, and vibrational properties of other emerging layered materials.

Room temperature hydrogen and hydrocarbon sensors based on single nanowires of metal oxides

Hydrogen sensing characteristics of single nanowires of ZnO, TiO2 and WO2.72 have been investigated by contact mode atomic force microscopy. All these nanostructures are able to sense hydrogen, but the WO2.72 nanowire (40 nm diam) exhibits the highest sensitivity of 22 for 1000 ppm at 298 K. The WO2.72 nanowire is also found to be good at sensing aliphatic hydrocarbons in the form of liquefied petroleum gas with a sensitivity of 15 for 1000 ppm at room temperature. A WO2.72 nanowire with a diameter of 40 nm shows better sensing characteristics than a nanowire of 16 nm diameter.

High-sensitivity hydrocarbon sensors based on tungsten oxide nanowires

Hydrocarbon (LPG) sensors based on the nanostructures of V2O5 do not exhibit satisfactory characteristics, while sensors based on WO2.72 nanowires show high sensitivity (∼1800) for 2000 ppm of LPG at 200 °C as well as relatively short recovery and response times. Impregnation of WO2.72 nanowires with Pt in the 0.1–1.0 at% range, significantly improves the sensor characteristics, the sensitivity increasing with Pt concentration and reaching a value of ∼106 for 2000 ppm of LPG in the 100–200 °C range with 1 at% Pt. The sensitivity remains high even for 50 ppm of LPG, and is not affected significantly by repeated cycles or humidity. The mechanism of sensing of hydrocarbons by WO2.72 nanowires is explained on the basis of adsorbed oxygen species.

Enhanced field emission properties of doped graphene nanosheets with layered SnS2

We report here our experimental investigations on p-doped graphene using tin sulfide (SnS2), which shows enhanced field emission properties. The turn on field required to draw an emission current density of 1 μA/cm2 is significantly low (almost half the value) for the SnS2/reduced graphene oxide (RGO) nanocomposite (2.65 V/μm) compared to pristine SnS2 (4.8 V/μm) nanosheets. The field enhancement factor β (∼3200 for the SnS2 and ∼3700 for SnS2/RGO composite) was calculated from Fowler-Nordheim (F-N) plots, which indicates that the emission is from the nanometric geometry of the emitter. The field emission current versus time plot shows overall good emission stability for the SnS2/RGO emitter. The magnitude of work function of SnS2 and a SnS2/graphene composite has been calculated from first principles density functional theory (DFT) and is found to be 6.89 eV and 5.42 eV, respectively. The DFT calculations clearly reveal that the enhanced field emission properties of SnS2/RGO are due to a substantial lowe...

Freeze-dried WS2 composites with low content of graphene as high-rate lithium storage materials

Few layered WS2–graphene nanosheet composites are prepared by a simple and scalable hydrothermal reaction and a subsequent freeze-drying method. The freeze-dried WS2–graphene composite exhibits good cycling stability and outstanding high-rate capability of lithium storage. The reversible capacity remains 647 mA h g−1 after 80 cycles at a current density of 0.35 A g−1. Comparable capacities of 541 and 296 mA h g−1 can still be maintained when cycling at even higher current densities of 7 and 14 A g−1 (7 and 14 mA cm−2) respectively.