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Sol–gel dip coating method has been employed for the deposition of nanostructured single nickel oxide (NiO) and zinc oxide (ZnO) films and multilayered NiO/ZnO/NiO and ZnO/NiO/ZnO films. The structural, morphology and optical properties of prepared films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectroscopy, respectively. XRD analysis showed that ZnO-based films crystallized in write phase and presented an epitaxial orientation depending on the substrate. SEM images also showed uniform size distribution around 30–70 nm for all samples. Antibacterial effectiveness of NiO and ZnO- based films were tested against general Escherichia coli (E. coli ATCC 25922) and Streptococcus aureus (S. aureus, ATCC 29213) as Gram negative and Gram positive model, respectively, using the so-called drop-test method under UV light illumination and dark conditions. ZnO/NiO/ZnO film was found to be the most toxic among tested samples, followed by ZnO, NiO/ZnO/NiO and NiO films. Samples exposure to UV light resulted in higher activity compared to dark conditions against both E. coli and S. aureus, but considerably more effective in the former case. The obtained results were discussed according to the lattice matching between the heteroepitaxial films and structural modification as key roles on the preferential growth orientation and antibacterial activity.

Nickel oxide films were deposited onto glass substrates by sol–gel dip coating method using solvents of different polarities without any catalysts, templates or surfactants. Methanol, 1,4-butanediol, ethanol, and 2-propanol were used as solvents. The structural, optical and electrical properties of NiO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and Hall effect measurements, respectively. Nickel oxide thin films with cubic phase crystal structure of various preferred orientations were obtained in the different solvents. The XRD results showed that films deposited from solution using higher polar solvents develop a (1 1 1) preferred orientation, while the (2 0 0)-orientated films were obtained using lower polar solvents. The average particle size increases with viscosity of solvents. Surface morphology of the nickel oxide film consisted of nanoparticles with uniform coverage of the substrate surface. The solvent of higher viscosity induced larger particle size. Band gap narrowing from 4.42 to 3.87 eV was observed using different solvents. The lower resistivity and Hall coefficient was obtained for prepared NiO films using higher polar solvents. The relationships between solvent physicochemical properties, preferred orientation, structural, optical and electrical properties of NiO films were investigated.

The textile industry is characterized by high consumption of water, fuel, and chemicals. The wastewater treatment and recycling possibilities in the textile industry are environmentally of the highest importance. The most common chemical pollutants present in textile industry wastewater are the azo-dyes. The solution based sol–gel method was used to synthesize ZnO thin films using different solvents to evaluate the morphology-dependent photocatalytic activity toward the degradation of two azo dyes including sodium [3-[(4,5-dihydro- 3-methyl-5-oxo-1-phenyl-1H-pyrazol-4-yl)azo]-2-hydroxy-5-nitrobenzenesulp-honato (3-)] hydroxychromate (1-) and sodium (5-((4′-((2,6-dihydroxy-3-((2-hydroxy-5-sulfophenyl)azo)phenyl)azo)-4-biphenylylazo) salicylato (4-)) cuprate (2-) in water. 2-Propanol, methanol, ethanol, and 1,4-butanediol were used as solvents. The photocatalytic degradation rates depend on the dye structure and concentration, solvent-dependent ZnO film morphologies, pH of the medium and excitation light source. The observed rate constants of ZnO film prepared using 2-propanol and of ZnO film prepared using methanol were enhanced approximately by a factor of 3 under UV light and under visible light, respectively. The obtained results were discussed according to the structure and morphology of ZnO films as key parameters in photocatalytic activity.

In the present study, the effects of the heterojunctions on the optical and structural characteristics and the resulting photocatalytic properties of multilayered ZnO-based thin films were investigated. The junctions were composed of semiconducting ZnO nano-porous films coated on the In2O3 and SnO2 counterpart layers. The multilayered ZnO films based on the triple-layered Ag-doped indium oxide (AIO)/tin oxide (TO)/zinc oxide (ZnO), indium oxide (IO)/Ag-doped tin oxide (ATO)/zinc oxide (ZnO), indium oxide (IO)/tin oxide (TO)/zinc oxide (ZnO) and tin oxide (TO)/ indium oxide (IO)/zinc oxide (ZnO) have been fabricated by subsequent sol‐gel dip coating. Their structural and optical properties combined with photocatalytic characteristics were examined toward degradation of Solantine Brown BRL (C.I. Direct Brown), an azo dye using in Iran textile industries as organic model under UV light irradiation. Effects of operational parameters such as initial concentration of azo dye, irradiation time, solution pH, absence and presence of Ag doping and consequent of sublayers on the photodegradation efficiencies of ZnO nultilayered thin films were also investigated and optimum conditions were established. It was found that the photocatalytic degradation of azo dye on the composite films followed pseudo-first order kinetics. Photocatalytic activity of AIO/TO/ZnO interface composite film was higher compared with other films and the following order was observed for films activities: AIO/TO/ZnO > IO/TO/ZnO > ATO/IO/ZnO > TO/IO/ZnO. Differences in the film efficiencies can be attributed to differences in crystallinity, interfacial lattice mismatch, and surface morphology. Besides, the presence of Ag doping between layers that may act as trap for electrons generated in the ZnO over layer thus preventing electron‐hole recombination. # 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Nanostructure single ZnO, SnO2, In2O3 and composite ZnO/SnO2, ZnO/In2O3 and ZnO/SnO2/In2O3 films were prepared using sol–gel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO2 and In2O3 films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.

The nano-sized coupled oxides ZnO/SnO2 thin films in a molar ratio of 2:1 (Z2S), 1:1 (ZS) and 1:2 (ZS2) were prepared using sol–gel dip coating method and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectroscopy. Escherichia coli (E. coli, ATCC 25922) was selected as a model for the Gram-negative bacteria to evaluate antibacterial property of composite samples compared with single ZnO (Z) and single SnO2 (S) films. The antibacterial activity has been studied applying the so-called antibacterial drop test under UV illumination. The bactericidal activity was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The influence of the SnO2–ZnO nanocomposite composition on the structural features and on the antibacterial properties of the thin films are reported and discussed. It is found that all coatings exhibited a high antibacterial activity. The coupled oxide photocatalyst Z2S has better photocatalytic activity to bacteria inactivation than ZS, ZS2, Z and S films. Furthermore, nanostructured films were active even in the absence of irradiation.

Indium oxide (In 2 O 3 ), zinc oxide (ZnO), stannic oxide (SnO 2 ), and titanium dioxide (TiO 2 ) thin films were prepared on glass substrates using electron beam evaporation. The samples characterized by UV–vis spectroscopy, diffraction ray-X and scanning electron microscopy techniques. The photocatalytic degradation of methylene blue in an aqueous solution, as a model compound, was investigated using different metal oxides in an attempt to compare the decomposition reaction rate. The progress of degradation was monitored using UV–vis spectrophotometry. The effects of various experimental parameters such as initial concentration of methylene blue (5–10 mg/l), pH of the solution (2–8), annealing temperature (250–550 °C), and catalyst nature and its microstructure were systematically studied in order to achieve maximum degradation efficiency. The results obtained were fitted with the Langmuir–Hinshelwood model to study the degradation kinetics and discussed in detail. Nearly complete degradation was obtained at optimal operational parameters including the higher annealing temperature of thin film and the increase in MB solution pH. The degradation with In 2 O 3 was more efficient than with SnO 2 , ZnO and TiO 2 films.

Indium tin oxide (ITO) and titanium oxide (TiO2) thin films were deposited on glass substrates using electron beam evaporation. Amorphous and crystalline films can be obtained at different annealing temperatures. The thin films are characterized by UV–vis, XRD spectra and AFM analysis. The degradation of X6G (C.I. Reactive Yellow 2), commonly used as textile dye, can be photocatalyzed by ITO and TiO2 thin films. The degradation can be completed in the order of minutes at optimal operational parameters. Using advanced oxidation processes (AOPs) and comparison between photoactivity of both films reveal that, indium tin oxide can be used as a suitable alternative to TiO2 thin films for water treatment.

The photocatalytic degradation of a non-biodegradable azo dye called (C.I. Direct 80, Red Sulphonyl 3BL) was investigated using TiO2 thin films in aqueous solution under irradiation of a mercury lamp Philips (UV-C) light source. The effect of operational parameters, i.e., annealing temperature of thin film, substrate nature on which TiO2 films were deposited, film thickness, pH of the solution, dye concentration, and irradiation time on the degradation rate of azo dye aqueous solutions was examined. Results show that the employment of efficient photocatalyst and the selection of optimal operational parameters lead to complete decolorization. The best conditions for maximum photocatalytic degradation were found to be pH 1 at 5 ppm concentration of dye over TiO2 thin films deposited on glass substrate coated with indium-tin oxide having 350 nm thicknesses annealed at 550 °C. The samples are all in the complete anatase phase and the particle size is in nanometer scale which is confirmed by XRD pattern analysis.