Jalindar D. Ambekar

Template-free synthesis of nanostructured CdxZn1-xS with tunable band structure for H2 production and organic dye degradation using solar light

We have demonstrated a template-free large-scale synthesis of nanostructured Cd(x)Zn(1-x)S by a simple and a low-temperature solid-state method. Cadmium oxide, zinc oxide, and thiourea in various concentration ratios are homogenized at moderate temperature to obtain nanostructured Cd(x)Zn(1-x)S. We have also demonstrated that phase purity of the sample can be controlled with a simple adjustment of the amount of Zn content and nanocrystalline Cd(x)Zn(1-x)S(x = 0.5 and 0.9) of the hexagonal phase with 6-8 nm sized and 4-5 nm sized Cd(0.1)Zn(0.9)S of cubic phase can be easily obtained using this simple approach. UV-vis and PL spectrum indicate that the optical properties of as synthesized nanostructures can also be modulated by tuning their compositions. Considering the band gap of the nanostructured Cd(x)Zn(1-x)S well within the visible region, the photocatalytic activity for H2 generation using H2S and methylene blue dye degradation is performed under visible-light irradiation. The maximum H2 evolution of 8320 μmol h(-1)g(-1) is obtained using nanostructured Cd(0.1)Zn(0.9)S, which is four times higher than that of bulk CdS (2020 μmol h(-1) g(-1)) and the reported nanostructured CdS (5890 μmol h(-1)g(-1)). As synthesized Cd(0.9)Zn(0.1)S shows 2-fold enhancement in degradation of methylene blue as compared to the bulk CdS. It is noteworthy that the synthesis method adapted provides an easy, inexpensive, and pollution-free way to synthesize very tiny nanoparticles of Cd(x)Zn(1-x)S with a tunnable band structure on a large scale, which is quite difficult to obtain by other methods. More significantly, environmental benign enhanced H2 production from hazardous H2S using Cd(x)Zn(1-x)S is demonstrated for the first time.

Hierarchical nanostructures of CdIn2S4via hydrothermal and microwave methods: efficient solar-light-driven photocatalysts

We have demonstrated the synthesis of nanostructured CdIn2S4 with a fascinating ‘marigold flower’ morphology using a hydrothermal method, and mixed morphologies (flowers, spheres and pyramids) using a microwave method. In the microwave synthesis, the product was formed within 15 min, whereas by the hydrothermal method more than 24 h was required. In the microwave method, various capping agents were used that result in different particle morphologies. Hydrothermal formation of crystalline CdIn2S4 nanotubes in methanol showed a significant effect of reaction medium on morphology. Synthesis of these crystalline CdIn2S4 nanopyramids and ‘marigold flowers’ has also been demonstrated using microwave synthesis for the first time. An XRD study showed a cubic spinel structure for CdIn2S4 prepared by both methods. The band gap for CdIn2S4 was 2.27 eV when synthesized using the microwave method, and 2.23 eV using the hydrothermal method, implying that the microwave method produces a lower particle size than the hydrothermal method. A noteworthy aspect of this work is that we obtained novel ternary chalcogenide hierarchical nanostructures by simple hydrothermal and microwave methods. Considering that the band gap of the hierarchical CdIn2S4 is within the visible region, we compared its ability to photocatalytically degrade methylene blue (MB) with that of CdS. The marigold flowers, nanoparticle spheres and nanopyramids of CdIn2S4 synthesised by microwave method gave almost 30% enhancement in the degradation of MB as compared to CdS under direct sunlight. This is of importance, considering that CdIn2S4 has potential for applications in solar energy conversion and opto-electronic devices.

Hierarchical Nanostructured ZnO with Nanorods Engendered to Nanopencils and Pin-Cushion Cactus with Its Field Emission Study

In the present investigation, we report the synthesis of highly crystalline ZnO nanorods engendered to pin-cushion cactus and 1D nanopencil like nanoforms on zinc (Zn) foil via a simple sonochemical assisted hydrothermal route. The work reported herewith is attractive for two reasons: (i) the facile one step solution approach assisted by prior ultrasonication converts nanorods/nanobelts into nanopencils, and (ii) the sharp and quasi-aligned ZnO nanopencils are potential field electron emitters. In addition, the controlled growth of pinhole like ZnO nanopencils and aligned hexagonal ZnO nanodisc was obtained. The changes in the growth rate, diameter, density, and surface area of highly oriented ZnO nanorods are examined. Considering the significances of such novel morphologies, technically detailed formation mechanism has been proposed. The field emission study of pin-cushion cactus like ZnO nanopencils was performed. Field emission measurements demonstrate remarkably low turn-on field which is explained on the basis of a sequential enhancement mechanism involving the consecutive stem and tip contribution. The Folwer-Nordheim (F-N) plot showed nonlinear behavior indicating the semiconducting nature of the emitter. Significantly, emission current is stable at the preset value of 3 μA over the period of 3 h. The simplicity of the synthesis route coupled with the promising emission properties is envisaged to be an important candidate for potential nanoelectronic devices. These unique imperative ZnO nanostructures may have potential for sensors, solar cell, photocatalysis, varisters, etc.

P1.8.3 Ink-Jet Printed Conducting Polyaniline based Flexible Humidity Sensor

Ink-Jet Printed, Intrinsically Conducting Polymer (ICP), polyaniline have been used for humidity sensing at room temperature. Polyaniline based, aqueous ink-jet printable ink has been synthesized by single step, chemical oxidative polymerization technique. Sulphonic acids were used as a dopant during the in-situ polymerization process. This is a single step polymerization process for the direct synthesis of conducting emeraldine salt phase of the polymer as an ink formulation. The synthesized polyaniline ink was further characterized by spectroscopic (UV-Vis. and FT-IR) analysis which confirmed the presence of conducting emeraldine salt phase of the polymer. The viscosity of the ink was measured by using Brook-field viscometer. The successive trials were performed for the printing of IDT pattern on the flexible, untreated polymer substrate using HP ink-jet- printer. The printed sensor was subjected for the humidity sensing measurements. The change in the resistance with change in the %RH was observed. It is suggested that the increase in conductivity at high humidity may be related to a vapour-induced change in the transfer of charge carriers between the polymer chains. The synthesized polyaniline based ink can also be considered as a good candidate for variety of ink-jet printed low cost electronics devices.

Ag:BiVO4 dendritic hybrid-architecture for high energy density symmetric supercapacitors

We demonstrate the fabrication of Ag:BiVO4 with a dendritic architecture by a template free hydrothermal method. Then, symmetric cells based on Ag:BiVO4 electrodes were assembled which exhibit an extended voltage window of up to 1.6 V with an excellent energy density of 2.63 mW h cm−3 (38.43 W h kg−1) and a power density of 558 mW cm−3 (8.1 kW kg−1).

Architecture of the CdIn2S4/graphene nano-heterostructure for solar hydrogen production and anode for lithium ion battery

The facile single step template free synthesis of hierarchical CdIn2S4/graphene nano-heterostructures with multi-functionality as a photocatalyst for solar hydrogen production and as an anode for lithium ion battery has been demonstrated. The nanopetals of CdIn2S4 are decorated on the graphene which shows extended visible light absorption. Hence, the photocatalytic hydrogen evolution study is performed under solar light. The nano-heterostructure showed excellent photocatalytic activity (4495 μmol h−1 per 0.2 g) for hydrogen production. The enhanced photocatalytic activity is attributed to the inhibition of charge carrier recombination due to graphene which acts as an excellent electron collector and transporter. Furthermore, the use of nano-heterostructures as an anode for Li-ion batteries demonstrated very high reversible capacity i.e. 678 mA h g−1 which on cycling, kept at 608 mA h g−1 at an applied current of 150 mA g−1 for 225 cycles and exhibited good rate capability. The excellent Li-storage properties of the nano-heterostructures is associated with the hierarchical flower like structure, high porosity of CdIn2S4 and the fast electron kinetics offered by the graphene support.

Novel nanocrystalline zinc silver antimonate (ZnAg3SbO4): an efficient & ecofriendly visible light photocatalyst with enhanced hydrogen generation

Herein, we report zinc silver antimonate (ZnAg3SbO4)/ZAS, a novel visible light active photocatalyst for hydrogen generation. The XRD pattern confirmed the formation of a highly crystalline single phase orthorhombic ZAS. The FESEM and TEM micrographs exhibited that the size of the nanoparticles are in the range ∼20–30 nm. An optical study showed a broad absorption edge from 400 to 1000 nm, with an estimated band gap of about ∼1.48 eV. Considering this ideal band gap, ZAS was used as a photocatalyst for the photodecomposition of H2S under visible light irradiation to produce hydrogen for the first time. We obtained the utmost hydrogen evolution i.e., ∼10 200 μmol h−1 g−1 for the naked ZAS (without a co-catalyst) catalyst under visible light, which is much higher than the earlier reported photocatalysts. Generally, in complex oxides of p-block metals, the bottom of the conduction band (CB) consists of the merely localized s and/or p orbitals which are largely dispersed. This large dispersion is responsible for a high electron mobility and extremely high photocatalytic activity. Therefore, a complex oxide (ZAS) of Ag, Zn and the p-block metal (Sb) is found to be a promising visible light active photocatalyst. This is the most stable, efficient and eco-friendly novel visible light active oxide photocatalyst for hydrogen production.

Hierarchical CdS nanostructure by Lawesson's reagent and its enhanced photocatalytic hydrogen production

Lawessons reagent (LR) has been effectively exploited for the synthesis of hierarchical architectures of cadmium sulphide (CdS) nanostructures for the first time. The X-ray diffractograms of the as synthesised CdS nanostructures confirm the formation of hexagonal CdS. The broadness of the XRD peaks clearly indicates the nanocrystalline nature of CdS with average crystallite size of 4 nm. A FESEM study revealed the formation of hierarchical nanostructures, whereas a TEM study showed that the hierarchical arrangement is composed of nanosized CdS particles. A band-gap i.e. 2.4 eV was derived from diffuse reflectance spectroscopy. The photoluminescence spectrum showed an emission peak at 535 and 568 nm which can be attributed to band-edge emission and surface emissions or possible metal vacancies, respectively. Considering the band-gap within the visible region, the photocatalytic hydrogen evolution performance of these CdS nanostructures was performed under visible light irradiation from hydrogen sulphide and water, respectively. Utmost hydrogen evolution i.e. 14 136 μmol h−1 g−1 and 2065 μmol h−1 g−1 was observed over a naked CdS nanostructure via H2S and water decomposition, respectively. The amount of hydrogen obtained by H2S splitting is much higher as compared to earlier reports.

Synthesis of porous nitrogen doped zinc oxide nanostructures using a novel paper mediated template method and their photocatalytic study for dye degradation under natural sunlight

N-Doped zinc oxide (N-ZnO) nanostructures were prepared using a novel paper mediated template combustion method. The precursors were impregnated on filter papers and thermally processed to obtain porous N-ZnO nanostructures. The XRD patterns of the as-synthesized N-ZnO confirm the formation of the wurtzite phase, and the broad diffraction peaks confirm the nanocrystalline nature of the product. The TEM and SEM images show spherical shaped 20–30 nm N-ZnO nanoparticles. The UV-visible absorbance spectra of the product show a red shift in the spectra with increasing doping concentration of nitrogen in ZnO. This red shift was due to incorporation of nitrogen into the ZnO lattice. Photoluminescence spectra indicate a strong emission peak at 391 nm which corresponds to band gap emission. Considering the band gap of the as-synthesized N-ZnO to be well within the visible region, the photocatalytic activity for the degradation of methylene blue (MB) and rhodamine (RhB) dyes was studied under direct sunlight using the as-synthesized N-ZnO. The N-ZnO prepared with a higher amount of urea (1 : 8) shows the highest photocatalytic activity as compared to the other synthesized N-ZnO samples towards the degradation of MB and RhB, i.e. complete degradation of MB in 30 min and RhB in 45 min. Our novel synthesis approach provides uniformly distributed nanosized spherical particles having higher photocatalytic activity as compared to other reported methods.