Sudhir S. Arbuj

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.

One dimensional CdS/ZnO nanocomposites: an efficient photocatalyst for hydrogen generation

One-dimensional ZnO nanostructures were synthesized using solvothermal reaction method, and in situ CdS nanoparticles were grown on 1D ZnO having different CdS compositions such as 0.1, 0.5, 1 and 5 mol% using microwave reaction system. The prepared CdS/ZnO coupled semiconductor catalysts were characterized using various spectroscopic techniques. XRD analysis indicated the presence of a wurtzite structure for all the prepared CdS/ZnO compositions. DRS spectrum showed red shift in the absorbance edge of CdS/ZnO nanocomposites with increasing CdS mol% and absorbance increases in 400 to 500 nm range. Photoluminescence spectra illustrated two emission peaks, with the first one at 390 nm due to the band edge emission of ZnO and the second broad peak centered around 480 nm possibly due to CdS band edge emission or oxygen vacancies in ZnO. FESEM image showed the formation of pencil shaped one-dimensional ZnO nanorods containing spherical CdS nanoparticles on the surface of ZnO. TEM analysis confirms the rod-like morphology of ZnO and the presence of CdS nanoparticles. The activity of the prepared CdS/ZnO catalysts was evaluated by measuring the amount of H2 generated during photocatalytic H2 evolution from water. The photocatalytic activity of prepared coupled CdS/ZnO shows an increase in hydrogen generation compared to that of individual ones. CdS loading enhances the rate of H2 generation and is the highest for 5 mol% CdS/ZnO composition.

Flower shaped homocentric pencil like ZnO nanorod bundles: synthesis, characterisation and study of their photocatalytic activity

Flower shaped homocentric pencil like ZnO nanorod bundles are synthesized by a hydrothermal method. The PXRD pattern corresponds to the typical wurtzite structures of ZnO, which exhibits excellent activity as a photocatalyst for the degradation of malachite green under solar light irradiation.

Heterogeneous photocatalysed Heck reaction over PdCl2/TiO2

The heterogeneous PdCl2/TiO2 efficiently catalyzes the C–C bond formation (Heck reaction) between aryliodides and olefins under photochemical and mild reaction conditions. This process gives good to excellent conversion under optimized reaction conditions. After completion of the reaction, Pd2+ is reduced to Pd0. Further, Pd0 can be easily converted into Pd2+ by heating with ammonium chloride at 400 °C for 30 min and the regenerated catalyst could be reused up to the third recycle with good catalytic activity. The catalysts (before and after reaction, as well as regenerated) were systematically characterized using Transmission Electron Microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, temperature programmed reduction and DRUV-visible spectroscopy techniques.

Solar light driven dye degradation using novel organo–inorganic (6,13-pentacenequinone/TiO2) nanocomposite

The coupled semiconductor photocatalysts of 6,13-pentacenequinone/TiO2 (PQ/Ti) with different weight ratios were prepared. The PQ/TiO2 nanocomposite was prepared by a simple wet impregnation method. The prepared catalyst was characterized with various spectroscopic methods. XRD confirms the monoclinic and anatase phase of PQ and TiO2, respectively. FE-SEM showed the sheet like morphology of PQ, whereas the coupled catalyst depicts the formation of a homogeneous layer of TiO2 on the PQ surface in all three compositions. Optical studies by diffuse reflectance UV-Visible absorbance spectroscopy (DRS) indicate the band gap of PQ and TiO2 around 2.8 and 3.2 eV respectively. The absorbance in the range of 450 nm was also observed in the case of the prepared coupled catalyst confirming the loading of PQ on TiO2. The photocatalytic activity of the coupled catalyst was studied by observing the degradation of methylene blue (MB) dye under visible light irradiation. As compare to the individual components, the coupled organo–inorganic catalyst showed higher photocatalytic activity towards MB degradation. The PQ/TiO2 nanocomposite having 0.2 wt% PQ showed the highest rate of MB degradation i.e. Kapp = 5.2 × 10−2 min−1.

Novel Functionality of Organic 6,13-Pentacenequinone as a Photocatalyst for Hydrogen Production under Solar Light

6,13-Pentacenequinone (PQ), an intermediate for an organic semiconductor pentacene, was synthesized by single step solvent free solid state reaction at room temperature under ambient conditions which is hitherto unattempted. The phase purity has been confirmed by XRD and NMR. Optical study showed the absorption at 390 and 412 nm attributed to the π-π* and n-π* transitions, respectively. Cyclic voltammetry indicates the semiconducting nature of PQ having a band gap of 3 eV. The photoluminescence study revealed emissions at 408 and 432 nm. Considering the good thermal stability and absorption well within visible region, wisely, PQ has been used as a photocatalyst for the hydrogen production under solar light. Surprisingly we observed the utmost hydrogen evolution i.e. 4848 μmol/h/0.1 g (quantum efficiency 6.8%). The repeatability and reusability study confirmed the stability of the photocatalyst. The confirmation of the photocatalytic effect was also confirmed using methylene blue (MB) dye degradation under natural sunlight. The observed rate constant (Kapp) for photocatalytic MB degradation was 1.60 × 10(-2) min(-1). The use of an organic photocatalyst for hydrogen production has been demonstrated for the first time. This novel organic photocatalyst can also be explored for water splitting.

Hydrogen, ethanol and ammonia gas sensing properties of nano-structured titanium dioxide thick films

Pure nanocrystalline TiO2 thick films have been prepared by doctor blade technique on glass substrate. The nanostructural properties of the powder as well as thick films and gas sensing performance of the TiO2 thick films towards hydrogen, ethanol and ammonia gases have been studied and presented here. The experimental results revealed that these nanostructured TiO2 films are sensitive to different gases such as hydrogen, ammonia and ethanol at low operating temperature close to 55–65 °C. The TiO2 film shows highest sensitivity towards ammonia gas as compared to hydrogen and ethanol.

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.

One dimensional CdS nanostructures: heterogeneous catalyst for synthesis of aryl-3,3′-bis(indol-3-yl)methanes

Herein, we have developed a novel heterogeneous catalytic system for synthesis of bis(indol-3-yl)methanes using one dimensional (1D) CdS nanorods. CdS nanorods were synthesized by a solvothermal reaction technique at 200 °C over 12 h in the presence of ethylenediamine as a solvent. The prepared 1D CdS was characterized using various spectroscopic methods. X-ray diffraction (XRD) revealed the formation of highly crystalline CdS having a wurtzite structure. FESEM analysis confirms the formation of a rod like morphology with length around 150 to 200 nm and diameter ∼15 nm. TEM also validates the formation of uniform size one dimensional (1D) CdS nanostructures. The catalytic activity of 1D CdS as a Lewis acid was investigated for the synthesis of bis(indol-3-yl)methanes (BIMs) with various substituted aldehydes and indoles within shorter reaction time affording the corresponding product in excellent yield.

Template-free synthesis of Fe3O4 nanorod bundles and their highly efficient peroxidase mimetic activity for the degradation of organic dye pollutants with H2O2

Highly crystalline Fe3O4 nanorod bundles were synthesized via a facile template-free method. The high surface to volume ratio of Fe3O4 nanorods facilitates the excellent activation of H2O2via their peroxidase mimetic activity for the degradation of crystal violet (CV) as a model organic dye pollutant. The self sensitization of CV dye by solar irradiation also indirectly helps in the photo-Fenton-like degradation process.