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A combination of photocatalysis and biodegradation is a promising approach for the removal of xenobiotic organic compounds from wastewater, since photocatalysis cleaves the molecules into simpler intermediates that are later mineralized by microorganisms. Sequential photocatalytic and biological treatment (SPABT) consisting of ZnO as a photocatalyst and a microbial consortium (Galactomyces geotrichum and Brevibaccilus laterosporus) enhanced the degradation of a model textile dye, methyl red (MR). SPABT completely decolorized 500 mg MR/L within 4 h. Biotreatment alone required 6 h for 100% decolorization. A maximum of 70% decolorization was achieved with the photocatalytic treatment but reductions in COD and toxicity were not adequate. Significant elevated activities of enzymes, including azo reductase, laccase and veratryl alcohol oxidase, were observed in the microbial consortium after exposure of MR. The degradation pathway and products of MR varied with treatment applied. The persistent azo bond was cleaved by following photocatalytic treatment with the microbial biotreatment. Tests with Sorghum vulgare and Phaseolus mungo indicated the products obtained by SPABT were non-phytotoxic.

Zinc oxide (ZnO) thin films have been deposited onto fluorine doped tin oxide coated glass substrates by economical chemical spray pyrolysis technique. Films were deposited using various quantities of solution from 50 to 200 cc (substrate temperature 400°C, solution concentration 0·2M) in order to achieve different thicknesses. The films were characterised by X-ray diffraction, SEM, AFM and optical absorption techniques. The films exhibit a hexagonal wurtzite crystal structure with preferred (002) orientation. Morphological study showed a smooth and nanocrystalline surface of ZnO films. Direct optical band gap energy of ZnO thin films is found to be 3·24 eV. The average transmission is of the order of 87% in the visible region. The photoelectrocatalytic response of the film against Escherichia coli Davis is studied using a specially designed photoelectrochemical (PEC) reactor module. Thickness and UV light dependent photoelectrocatalytic bactericidal properties of ZnO thin films have been investig...

The nanocrystalline ZnO, TiO(2) and ZnO/TiO(2) films are deposited onto FTO-coated glass substrates by using spray pyrolysis technique. The structural, morphological, optical and photoelectrochemical properties of the ZnO, TiO(2) and ZnO/TiO(2) are investigated by X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy and photoelectrochemical techniques. XRD analysis shows that films are polycrystalline and having hexagonal and tetragonal crystal structure for pure ZnO and TiO(2). The photocatalytic degradation of methylene blue has been investigated with ZnO, TiO(2) and ZnO/TiO(2) photocatalysts. ZnO/TiO(2) thin films have proved quite effective mineralization of methylene blue, while pure ZnO and TiO(2) do not lead complete mineralization of methylene blue. The metabolites produced during degradation are analyzed by HPLC and Fourier transforms infrared spectroscopy. The by-products detected during degradation have been identified by GCMS technique.

Zinc oxide (ZnO) thin films have been successfully deposited onto fluorine doped tin oxide coated glass at substrate temperature of 400 °C and used as electrode in photoelectrocatalytic reactor. The untreated textile effluent was circulated through photoelectrocatalytic reactor under UVA illumination for the decolorization and degradation. Textile effluent was decolorized by 93% within 3h at room temperature with significant reduction in COD (69%). High performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy (FTIR) analysis of samples before and after decolorization confirmed the degradation of dyes molecules from textile effluent into simpler oxidizable products. Phytotoxicity study revealed reduction in toxic nature of textile effluent after treatment.

Thin films of zinc oxide have been deposited onto glass/FTO substrates at optimized 400 °C by using a chemical spray pyrolysis technique. Deposited films are character photocatalytic activity by using XRD, an SEM, a UV-vis spectrophotometer, and a PEC single-cell reactor. Films are polycrystalline and have a hexagonal (wurtzite) crystal structure with c-axis (002) orientation growth perpendicular to the substrate surface. The observed direct band gap is about 3.22 eV for typical films prepared at 400 °C. The photocatalytic activity of starch with a ZnO photocatalyst has been studied by using a novel photoelectrocatalytic process.