Zinc oxide (ZnO) photocatalysts were synthesized by sol–gel method using zinc acetate as precursor for degradation of azo dyes under UV irradiation. The resultant samples were characterized by different techniques, such as XRD, SEM, and EDX. The influence of preparation conditions such as calcination temperature and composite ratio on the degradation of methyl orange (MO) was investigated. ZnO prepared with a composite ratio of 4:1 and calcination temperature of 400 °C exhibited 99.70% removal rate for MO. The effect of operation parameters on the degradation was also studied. Results showed that the removal rate of azo dyes increased with the increased dosage of catalyst and decreased initial concentration of azo dyes and the acidic condition is favorable for degradation. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of azo dyes fitted the first-order kinetics and superoxide ions were the main species. The proposed photocatalyst can efficiently and rapidly degrade azo dyes; thus, this economical and environment-friendly photocatalyst can be applied to the treatment of wastewater contaminated with synthetic dyes.

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A novel strategy of coupling Mie's scattering effect into the lightabsorption region of TiO 2 was developed to enhance the photocatalytic performance of H 2 evolution over TiO 2 spheres. The TiO 2 spheres with different diameters (330− 750 nm) were controllably fabricated via adopting different sized polymer poly(methyl methacrylate) (PMMA) templates. The UV−visible absorption and reflectance spectra were employed for studying the absorption and scattering properties of these TiO 2 spheres. It was found that the scattering resonant peaks that indicate the strongly efficient scattering in different wavelength regions were largely dependent on the sizes of the TiO 2 spheres. The scattering resonant peaks have been detected around 366, 400, and 440 nm for the TiO 2 spheres with diameters of 380, 450, and 600 nm, respectively. Moreover, the photocatalytic efficiency of the H 2 evolution was found to be dependent on the size of the TiO 2 spheres. Among them, the TiO 2 spheres with a diameter of 380 nm exhibited the highest photocatalytic activity (313 μmol/(h·m 2 )), about 5 times and 3 times of that of 330 and 450 nm sized TiO 2 spheres, respectively. The highest activity observed on 380 nm sized TiO 2 may be attributed to its optimized diameter, which can result in a highly efficient scattering effect in the light-absorption region of TiO 2 (λ < 387 nm).