Bharat B. Kale

Nanowires of silver-polyaniline nanocomposite synthesized via in situ polymerization and its novel functionality as an antibacterial agent.

Silver-polyaniline (Ag-PANI) nanocomposite was synthesized by in situ polymerization method using ammonium persulfate (APS) as an oxidizing agent in the presence of dodecylbenzene sulfonic acid (DBSA) and silver nitrate (AgNO(3)). The as synthesized Ag-PANI nanocomposite was characterized by using different analytical techniques such as UV-visible (UV-vis) and Fourier transform Infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). UV-visible spectra of the synthesized nanocomposite showed a sharp peak at ~420 nm corresponding to the surface plasmon resonance (SPR) of the silver nanoparticles (AgNPs) embedded in the polymer matrix which is overlapped by the polaronic peak of polyaniline appearing at that wavelength. Nanowires of Ag-PANI nanocomposite with diameter 50-70 nm were observed in FE-SEM and TEM. TGA has indicated an enhanced thermal stability of nanocomposite as compared to that of pure polymer. The Ag-PANI nanocomposite has shown an antibacterial activity against model organisms, a gram positive Bacillus subtilis NCIM 6633 in Mueller-Hinton (MH) medium, which is hitherto unattempted. The Ag-PANI nanocomposite with monodispersed AgNPs is considered to have potential applications in sensors, catalysis, batteries and electronic devices.

An eco-friendly, highly stable and efficient nanostructured p-type N-doped ZnO photocatalyst for environmentally benign solar hydrogen production

We have investigated an economical green route for the synthesis of a p-type N-doped ZnO photocatalyst by a wet chemical method. Significantly, hazardous H2S waste was converted into eco-friendly hydrogen energy using the p-type N-doped ZnO photocatalyst under solar light, which has previously been unattempted. The as-synthesized p-type N-doped ZnO shows a hexagonal wurtzite structure. The optical study shows a drastic shift in the band gap of the doped ZnO in the visible region (3.19–2.3 eV). The doping of nitrogen into the ZnO lattice is conclusively proved from X-ray photoelectron spectroscopy analysis and Raman scattering. The morphological features of the N-doped ZnO are studied from FESEM, TEM and reveal particle sizes to be in the range of ∼4–5 nm. The N-doped ZnO exhibits enhanced photocatalytic hydrogen generation (∼3957 μmol h−1) by photodecomposition of hydrogen sulfide under visible light irradiation, which is much higher as compared to semiconductor metal oxides reported so far. It is noteworthy that a green catalyst is investigated to curtail H2S pollution along with production of hydrogen (green fuel) using solar light, i.e., a renewable energy source. The green process investigated will have the potential to synthesize other N-doped metal oxides.

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.

A Facile Template-Free Approach for the Large-Scale Solid-Phase Synthesis of CdS Nanostructures and Their Excellent Photocatalytic Performance

The simple, template-free, low-temperature, large-scale synthesis of nanostructured CdS with the hexagonal wurtzite phase from bulk cadmium oxide under solid-phase conditions is demonstrated for the first time. The novel approach involves the homogenization of cadmium oxide (CdO) and thiourea in various stoichiometric ratios at moderate temperature. Among the different molar ratios of CdO and thiourea studied, the CdO/NH(2) CSNH(2) molar ratio of 1:2 is found to be the best to obtain highly pure CdS. The obtained CdS nanostructures exhibit excellent cubic morphology and high specific surface area with a particle size in the range of 5-7 nm. The bandgap of the nanostructured CdS is in the range of 2.42 to 2.46 eV due to its nanocrystalline nature. In photoluminescence studies, emission is observed at 520.34 and 536.42 nm, which is characteristic of the greenish-yellow region of the visible spectrum. Considering the bandgap of the CdS is within the visible region, the photocatalytic activity for H(2) generation and organic dye degradation are performed under visible-light irradiation. The maximum H(2) evolution of 2945 μmol h(-1) is obtained using nanostructured CdS prepared in the 1:2 ratio, which is three times higher than that of bulk CdS (1010 μmol h(-1) ). CdS synthesized using the 1:2 molar ratio shows maximum methylene blue degradation (87.5%) over a period of 60 min, which is approximately four times higher than that of bulk CdS (22%). This amazing performance of the material is due to its nanocrystalline nature and the high surface area of the CdS. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology, and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal sulfides.

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.

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.

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.

Confinement of nano CdS in designated glass: a novel functionality of quantum dot–glass nanosystems in solar hydrogen production

The present work is the investigation of our novel approach to designing quantum dot–glass nanosystems by confining nano CdS in designated glass and the first employment of such a quantum dot system in solar hydrogen production. The CdS quantum dots were grown in a special glass matrix, which involved a sequence of steps. The obtained glass was of uniformly bright yellow in color and the bulk glass was pulverized to a fine powder of micron size particles. The glass powder was characterized structurally and morphologically. X-Ray diffraction and electron diffraction patterns reveal a hexagonal crystallite system for the CdS quantum dots. Field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy and chemical leaching with HCl studies demonstrate that the 2.5 nm size CdS quantum dots distribute homogeneously in a monodispersed form in the glass domain and on the surface with a “partially embedded exposure” configuration. This disposition imparts an excellent photostability against photocorrosion and also a facile catalytic function. Therefore, even a very small amount of CdS quantum dots (0.005 g per gram of glass powder) is able to photodecompose H2S under visible light (λ ≥ 420 nm) both in alkaline and pure aqueous media and produce solar hydrogen with markedly high quantum yields of 17.5 and 11.4%, respectively at 470 nm. Salient features like reusability after simple washing, corrosionless-stability and remarkable catalytic activity of this quantum dot–glass nanosystem are brought forth by our novel catalyst design and are much acclaimed in large scale solar H2 production.

In situ preparation of N–ZnO/graphene nanocomposites: excellent candidate as a photocatalyst for enhanced solar hydrogen generation and high performance supercapacitor electrode

We have demonstrated a facile in situ wet chemical method to synthesize nanostructured nitrogen doped ZnO/Graphene (N–ZnO/GR) nanocomposites for the first time. Nitrogen doped ZnO over graphene (N–ZnO/GR) was studied using various concentrations of graphene. During the synthesis of N–ZnO/GR nanocomposites, in situ formation of graphene via GO reduction and formation of 4–9 nm N–ZnO have been demonstrated. The composite N–ZnO/GR absorbs in the visible region and this property is used for the photocatalytic reaction to transform hazardous H2S waste into eco-friendly hydrogen using solar light. The N–ZnO/GR nanocomposite with 0.3% graphene exhibits an enhanced photocatalytic stable hydrogen production rate i.e. ∼5072 μmol h−1 under visible light irradiation. It is noteworthy that the N–ZnO/GR electrode exhibits a high specific capacitance of 555 F g−1 and excellent cyclic performance with nearly 96.20% capacity retention after 2000 cycles at a current density of 10 A g−1. These results indicate great potential applications of N–ZnO/GR in developing high hydrogen production and supercapacitors with high energy and power densities.

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.