Sambhaji S. Warule

Ecofriendly hydrogen production from abundant hydrogen sulfide using solar light-driven hierarchical nanostructured ZnIn2S4 photocatalyst

It is quite well-known that refineries are producing huge amount of H2S which has been used to produce sulphur and water using the well-known Claus process. This process is not an economically viable process, due to the high-cost chemical process and creates further acute environmental problems. Therefore, we have demonstrated the conversion of poisonous H2S into H2 using an ecofriendly phocatalysis process which is a green unconventional energy source. We have investigated ecofriendly nanostructured ZnIn2S4 photocatalyst to produce hydrogen from H2S using solar light. We also demonstrate the controlled synthesis of hierarchical nanostructured ZnIn2S4 using a facile hydrothermal method. The morphologies obtained have been greatly influenced by the presence of triethylamine (TEA) with various concentrations during the reaction. Surprisingly, a highly crystalline hexagonal layer structured ZnIn2S4 was obtained instead of cubic spinel. The hierarchical nanostructure, i.e. marigold flower-like morphology, was obtained without any surfactant. The thin and transparent petals self-assembled to form the unique nanostructured marigold flower. The highly crystalline puffy marigold flowers and nanoplates/nanostrips were obtained using TEA-assisted hydrothermal synthesis. Optical study shows the band gap in the range of 2.34–2.48 eV. Considering the band gap in the visible region, ZnIn2S4 is used as photocatalyst for hydrogen production from hydrogen sulphide under solar light which is hitherto unattempted. The constant photocatalytic activity of hydrogen evolution, i.e. 5287 μmol h−1, was obtained using such hierarchical nanostructured ZnIn2S4 under visible light irradiation. It is noteworthy that the H2 evolution rate obtained is much higher compared to earlier reported photocatalysts. Considering the significance of morphologies for photocatalytic application, the formation mechanism has also been furnished. The unique hierarchical nanostructured ZnIn2S4 ternary semiconductor having hexagonal layer will have potential applications in solar cells, LEDs, charge storage, electrochemical recording, thermoelectricity and other prospective electronic and optical devices.

Organization of cubic CeO2 nanoparticles on the edges of self assembled tapered ZnO nanorods via a template free one-pot synthesis: significant cathodoluminescence and field emission properties

The present investigation explores the controlled architecture of a CeO2–ZnO nanocomposite via a template-free, low temperature, facile single step solvothermal approach. This complex architecture depicts cubic single crystalline CeO2 nanoparticles (size ∼15 nm) grown on the edges of tapered ZnO nanorods with definite orientations and alignments. The formation of wurtzite ZnO, cubic CeO2 and the coexistence of Ce3+ and Ce4+ on the surface of the CeO2–ZnO nanocomposites are confirmed using various characterization tools. The finding of such unique nanostructures by a facile method is exemplified by a plausible growth mechanism. Surprisingly, the aqueous mediated ultrasonication reaction conferred the formation of crystalline ZnO nanotubes of diameter ∼50 nm. Spatially resolved cathodoluminescence spectra are obtained by linearly scanning an individual CeO2–ZnO nanorod along its length, which reveals the size-dependent surface effects. Interestingly, such hybrid CeO2–ZnO nanoarchitecture is observed to exhibit enhanced field emission properties, demonstrating better current stability as compared to other ZnO nanostructures. This is attributed mainly to strong surface interactions between the Ce-ionic species and the ZnO nanorods. Herein, a soft-chemical approach is used for the first time to architect a binary oxide nanostructure, which is otherwise accomplished using high temperature techniques, as reported elsewhere. Also, the present work not only gives insight into understanding the hierarchical growth behaviour of the CeO2–ZnO nanocomposite in a solution phase synthetic system, but also provides an efficient route to enhance the field emission performance of ZnO nanostructures, which could be extended to other potential applications, such as chemical sensors, optoelectronic devices and photocatalysts.

Vapor-liquid-solid growth of one-dimensional tin sulfide (SnS) nanostructures with promising field emission behavior.

Single-crystalline ultralong tin sulfide (SnS) nanowires has been grown by a thermal evaporation technique under optimized conditions on gold-coated silicon substrates, and for the first time, field emission investigations on the SnS nanowires at the base pressure of 1 × 10(-8) mbar are reported. It has been revealed that the surface morphology of the as-synthesized SnS nanostructures is significantly influenced by the deposition temperature and duration. Structural and morphological analyses of as-synthesized SnS nanostructures have been carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). To understand the optical and electronic properties of as-synthesized SnS nanowires, ultraviolet-visible (UV-vis), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) studies were carried out. The SEM and TEM measurements reveal the formation of ultralong SnS nanowires, with an average diameter of 80 nm. A plausible explanation on the vapor-solid-liquid (VLS) growth mechanism based on the experimental results and reported literature has been presented. Furthermore, the field emission characteristics of the SnS nanowires are found to be superior to the other metal chalcogenide nanostructures. The synthesized SnS nanowire emitter delivers a high current density of ∼2.5 mA/cm(2) at an applied electric field of ∼4.55 V/μm. The emission current stability over a period of 6 h is observed to be good. The observed results demonstrate the potential of the SnS nanowire emitter as an electron source for practical applications in vacuum nano/microelectronic devices.

Novel sonochemical assisted hydrothermal approach towards the controllable synthesis of ZnO nanorods, nanocups and nanoneedles and their photocatalytic study

ZnO nanovariants possessing different morphologies have been synthesized via a sonochemical as well as a sonochemical assisted hydrothermal (SAH) method. The synthesis process variables such as concentration of the precursors, ultrasonic irradiation period and duty cycle are observed to influence the resultant morphology of the ZnO nanostructures. Novel and significant morphologies of the ZnO nanostructures such as nanoneedles, tetrapods, nanowires, nanopetals, self assembled hexagonal rods and nanocups have been successfully obtained by controlling the process parameters. The surface morphology of the ZnO nanostructures was investigated using a scanning electron microscope (SEM). The SEM investigations showed that the nanoneedles originate from the hexagonal tube. Transmission electron microscope (TEM) analysis clearly demonstrates the nanocrystalline nature of the ZnO structures with unique morphologies like hexagonal nanocups. The ZnO nanostructures were characterized by UV-visible and photoluminescence spectrometers and a possible growth mechanism of the ZnO nanostructures is proposed. The photocatalytic activity of these nanostructures has also been presented. The ZnO nanostructures like nanocups and nanoneedles exhibit an excellent photocatalytic activity. Being a wide band gap semiconductor, these unique nanostructures will have a prospective application in ZnO based dye sensitized solar cells.

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.

Decoration of CdS nanoparticles on 3D self-assembled ZnO nanorods: a single-step process with enhanced field emission behaviour

A well-defined CdS–ZnO heteroarchitecture has been synthesized via a facile single-step hydrothermal approach. The morphological and structural studies reveal the formation of 3D nano-architectures, in which self-assembled ZnO nanorods (diameter ~50 nm) are well decorated with single crystalline CdS nanoparticles (size ~10 nm). The CdS–ZnO heteroarchitecture exhibits a remarkable change in the optical absorption due to the surface modification of ZnO nanorods by CdS. Surprisingly, under identical reaction conditions, the global ZnS nanoparticles are selectively grown at the apex of ZnO nanorods on the Zn substrate. Furthermore, a plausible growth mechanism has been presented on the basis of experimental results. Interestingly, the CdS–ZnO heteroarchitecture shows enhanced field emission properties such as low turn-on field, high emission current density and better current stability in comparison to other ZnO-based nanostructures. The present CdS–ZnO heteroarchitecture could be extended to other potential applications, such as chemical sensors, photodetectors, optoelectronic devices, and photocatalysts.

Single step hydrothermal approach for devising hierarchical Ag–ZnO heterostructures with significant enhancement in field emission performance

Hierarchical Ag–ZnO heterostructures have been synthesized via a template free single step hydrothermal method. Structural and morphological studies reveal the formation of heterostructures comprised of Ag nanoparticles (∼20 nm) organized on tapered ZnO nanorods under the prevailing experimental conditions. A plausible reaction and growth mechanism has been discussed. Furthermore, the hierarchical creation of ZnO with Ag as a relatively low work function material offers an effective approach to tailor its field emission properties. The field emission studies reveal a remarkable low turn-on field of ∼ 1 V μm−1, corresponding to an emission current density of ∼10 μA cm−2, and an emission current density of ∼400 μA cm−2 has been drawn at an applied field of 2.24 V μm−1. In addition, the Ag–ZnO heterostructures exhibit a good emission current stability at the pre-set value of ∼1 and 4 μA over a duration of 3 h. The enhancement of the field emission characteristics resulting from Ag nanoparticles decorating the tapered ZnO nanorods is discussed on the basis of band structure modifications. The ease of the synthesis route and the remarkable field emission properties offer Ag–ZnO heterostructures as a promising electron source for high current density applications.

Controlled synthesis of aligned Bi2S3 nanowires, sharp apex nanowires and nanobelts with its morphology dependent field emission investigations

Well-aligned ultra-long Bi2S3 nanowire arrays with three kinds of apex morphology – abruptly sharpened apex, thin belt and flat – have been systematically fabricated on tungsten (W) foil by a facile hydrothermal method. The structural and morphological studies reveal formation of distinct tip morphologies, possessing high aspect ratio, single crystalline nature and growth along the orthorhombic [001] axis. A plausible growth mechanism has been proposed on the basis of observed experimental results. The field emission properties of Bi2S3 nanowires and sharp apex Bi2S3 nanowires are investigated. From the field emission studies, the values of the turn-on field, required to draw emission current density of ∼0.1 μA cm−2, are observed to be ∼2.01 and 1.21 V μm−1 for nanowires and sharp apex nanowires, respectively. Furthermore, ultra-long Bi2S3 nanowires are also grown on the W microtip (brush-like) from which very high emission current density ∼11 mA cm−2 has been drawn. These results are helpful for the design, fabrication and optimization of integrated field emitters using 1D nanostructures as cold cathode material.

Quantum dot CdS coupled Cd2SnO4 photoanode with high photoelectrochemical water splitting efficiency

Quantum dot (QD) coupled wide band gap semiconductors such as TiO2 and ZnO have shown enhanced photoelectrochemical (in solar cells as well as water splitting) performance due to extended visible light absorption facilitated by QDs, compounded with favourable energetics for charge injection into the conduction band of the host semiconductor. In this work we investigate a new interesting system in this context, namely cadmium tin oxide (Cd2SnO4) coupled with CdS QDs. We find that the Cd2SnO4 photoanode, despite having a similar bandgap to that of CdS (2.2–2.5 eV), exhibits a very large (>40 fold) enhancement in the efficiency only when coupled to CdS QDs. By employing various microstructural, optoelectronic and photoelectrochemical characterization techniques we show that the favourable energetics and charge transport properties of Cd2SnO4 play the most crucial role in the enhancement of the photoelectrochemical performance. Our work suggests that it may be possible to design highly efficient photoelectrochemical systems by tailoring the constitution of nanocomposites based on the relatively less studied ternary oxide–sulphide heterosystems.

Architecture of rose and hollow marigold-like ZnIn2S4 flowers: structural, optical and photocatalytic study

In the present investigation, a surfactant-assisted hydrothermal route has been employed to design self-assembled rose and hollow marigold-like ZnIn2S4 flowers. In the absence of the surfactant, uniform (∼3–5 μm) marigold-like flowers are observed. The self-alignment of the transparent petals (∼3–5 nm thick with a length of ∼25–100 nm) leads to the formation of hollow marigold-like flowers, for which a plausible growth mechanism has also been proposed. Moreover, DEA assisted ZnIn2S4 demonstrates a rose flower-like via self assembly of hexagonal nanoplates. Structural and optical characterization shows the existence of hexagonal structures with a band gap in the range of ∼2.4–2.6 eV. Considering the ideal band gap in the visible region, we have used such unique nanostructured self assemblies of ZnIn2S4 as photocatalysts and demonstrated visible light-driven photocatalytic production of clean hydrogen by toxic hydrogen sulphide, which is abundantly available as a waste gas from oil refineries (15–20%). We believe that continuous efforts in this direction may open up new insights into the design of controllable nanostructures and their potential applications in advanced fields.