Suresh Gosavi

Plasmon-assisted photonics at the nanoscale

Plasmons are collective oscillations of electrons that have been exploited in many applications by manipulating and guiding light at resonant frequencies. The transition from understanding the origin and fundamentals of surface plasmon resonance to its many revolutionary applications has been intriguing. Advances in nanofabrication techniques over the last few years have led to variety of applications such as high-resolution plasmon printing, nanoscale waveguides, biodetection at the single-molecule level and enhanced transmission through sub-wavelength apertures, which are all examples of plasmon-assisted nanophotonics. Fundamental aspects of the surface plasmon resonance underlie enticing applications in nanophotonics.

Sulfite reductase‐mediated synthesis of gold nanoparticles capped with phytochelatin

An enzymatic synthesis route to peptide‐capped gold nanoparticles has been developed. Gold nanoparticles were synthesized using α‐NADPH‐dependent sulfite reductase and phytochelatin in vitro. The gold ions were reduced in the presence of the enzyme sulfite reductase, leading to the formation of a stable gold hydrosol of dimensions 7–20 nm and were stabilized by the capping peptide. The nanoparticles were characterized by X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy and UV–visible optical absorption. These studies will help in designing a rational enzymatic strategy for the synthesis of nanomaterials of different chemical compositions, shapes and sizes as well as their separation.

Controlled synthesis of ZnO from nanospheres to micro-rods and its gas sensing studies

1D ZnO rods are synthesized using less explored hydrazine method. Here we find, besides being combustible hydrazine can also be used as a structure-directing agent. The ratio of zinc nitrate (ZN) to hydrazine is found to control the morphology of ZnO. At lower concentration of ZN as compared with hydrazine the morphology of ZnO is found to be spherical. As we increase the hydrazine content the morphology changes from spherical (diameter approximately 100 nm) to the elongated structures including shapes like Y, T as well dumbbell (diameter approximately 40 nm and length approximately 150 nm). Interestingly for more than 50% of hydrazine ZnO micro-rods are formed. Such rods are of diameter approximately 120 nm having length of about 1 microm for ZN to hydrazine ratio of 1:9, isolated as well as bundle of rods are seen in scanning electron microscopy (SEM). The X-ray diffraction (XRD) reveals the phase formation with average particle size of 37 nm as calculated using Scherrers formula. The high-resolution transmission electron microscopy (HRTEM) is also done to confirm the d-spacing in ZnO. Gas sensing study for these samples shows high efficiency and selectivity towards LPG at all operating temperatures. Photoluminescence (PL) study for these samples is performed at room temperature to find potential application as photoelectric material.

Formation of gold nanoparticles in polymethylmethacrylate by UV irradiation

Gold–polymethylmethacrylate (PMMA) nanocomposites were fabricated with a photoreduction method using UV irradiation. The irradiated samples are compared with unirradiated ones to investigate the mechanism of gold nanoparticle formation and the effect of UV irradiation and polymer matrix on the morphology of the particles. The triangular gold nanoparticles were formed in polymer medium at a specific concentration of gold salt and UV exposure. The particle size decreased when the gold salt to polymer ratio was increased. The samples were analysed using UV–Vis spectroscopy, Fourier transform infrared spectrometry, atomic force microscopy, x-ray diffraction, small angle x-ray scattering and x-ray photoelectron spectroscopy. The interfacial interaction of Au nanoparticles and PMMA polymer has been discussed.

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.

Removal of hexavalent chromium ions by Yarrowia lipolytica cells modified with phyto-inspired Fe0/Fe3O4 nanoparticles

The removal of hexavalent chromium [Cr (VI)], an important ground water pollutant by phyto-inspired Fe(0)/Fe(3)O(4) nanocomposite-modified cells of Yarrowia lipolytica (NCIM 3589 and NCIM 3590), was investigated. Electron microscopy and magnetometer studies indicated an effective modification of yeast cell surfaces by the nanocomposites. The effect of pH, temperature, agitation speed, contact time and initial metal ion concentration on the removal of Cr (VI) was determined. The specific uptake values at pH 2.0 were 186.32±3.17 and 137.31±4.53 mg g(-1) for NCIM 3589 and NCIM 3590, respectively, when 1000 mg L(-1) of metal ion concentrations were used. The equilibrium data fitted to Scatchard, Langmuir and linearized Freundlich models suggesting that adsorption played a role in the removal of Cr (VI) ions. The surface modified yeast cells displayed higher values of Langmuir and Scatchard coefficients than the unmodified cells indicating that the former were more efficient in Cr (VI) removal. The enhanced detoxification of Cr (VI) ions by this composite material could be attributed to the reductive power of the Fe(0)/Fe(3)O(4) nanocomposites as well the yeast cell surface functional groups.

Characterization of SnO2-based H2 gas sensors fabricated by different deposition techniques

Thick and thin films of SnO2 are extensively used for resistive gas sensors. Characteristics are compared for films produced by four different techniques – chemical vapour deposition (CVD), spray pyrolysis, vacuum evaporation and screen printing. The films are characterized for H2 sensing only, using a static measurement system to investigate their temperature selectivity. The samples are tested at a concentration of 300 p.p.m. H2 gas, a typical value for comparison. No selective peak is observed for CVD and spray deposited samples, and the selective peak for vacuum evaporated samples has a low sensitivity. But the selective peak for screen printed samples has a sensitivity of 55% (δR/Rair). And what is more, the screen printed samples have a repeatable response.

Electrochemical polymerization of poly(o-anisidine) thin films: effect of synthesis temperature studied by cyclic voltammetry

The effect of temperature on the electrochemical synthesis of poly(o-anisidine) (POA) thin films has been investigated. The POA films were synthesized electrochemically under cyclic voltammetric conditions in aqueous solutions of H2SO4 at various temperatures between -6°C and 40°C. These films were characterized by cyclic voltammetry (CV), UV–visible spectroscopy and scanning electron microscopy (SEM). It has been found that the rate of polymer formation depends on the synthesis temperature and is highest at 15°C. The optical absorption spectra indicate a major peak at about 800nm and a shoulder at about 440nm independent of the synthesis temperature. The peak at about 800nm corresponds to the presence of the emeraldine salt phase of POA, while the latter may be attributed to the formation of radical cations. The absorbance and width of the peak at about 800nm is observed to increase at low synthesis temperatures. The POA film synthesized at 15°C shows predominant formation of the emeraldine salt phase of POA. The surface morphology as revealed by SEM, is observed to depend on the synthesis temperature, and is caused by different rates of polymer formation at different temperatures.

Synthesis and analysis of ZnO and CdSe nanoparticles

Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.

A novel template free, one pot large scale synthesis of cubic zinc sulfide nanotriangles and its functionality as an efficient photocatalyst for hydrogen production and dye degradation

Herein, we have demonstrated a novel, facile, template free method for the synthesis of nanostructured zinc sulfide from bulk zinc oxide. This synthesis method may provide an easy, inexpensive and pollution free way to synthesize nanostructured zinc sulfide on a large scale. Zinc oxide and thiourea in various stoichiometric ratios were homogenized at moderate temperature to obtain zinc sulfide. The phase pure nanostructured cubic zinc sulfide was obtained using a 1 : 2 molar ratio of zinc oxide & thiourea and in excess of thiourea as well. Surprisingly, monodispersed nanotriangles of zinc sulfide were obtained using all molar ratios of zinc oxide and thiourea. The nanotriangles of size 5–6 nm were obtained for zinc sulfide of a 1 : 2 molar ratio. The band gap of nanostructured zinc sulfide was observed to be in the range of 3.86 to 3.75 eV, which is higher than that of the reported value. The blue shift was obtained due to the nanocrystalline nature of the zinc sulfide. Considering the significant morphology of zinc sulfide, it has been used as a photocatalyst for water splitting to produce hydrogen and for degradation of methylene blue as well. The hydrogen evolution rate was observed to be 2050 μmol h−1 g−1, which is much more than the bulk zinc sulfide (410 μmol h−1 g−1) as well as reported nanostructured ZnS. Three fold enhancements in the degradation of methylene blue as compared to bulk zinc sulfide have also been observed. 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.