The insight of porous structure and structural defects on the photoactive properties of ZnO-SiO2 and SiO2 nanopowders prepared by modified sol-gel method

ZnO-SiO2 grainy and porous nanopowders were synthesized by the modified sol-gel method using polyvinylpyrrolidone additions. The crystal structure, morphology, spectral, luminescent and photocatalytic properties of obtained nanopowders were studied. The influence of the ZnO/SiO2 molar ratio, polyvinylpyrrolidone additions, and the temperature of thermal treatment on the structure and properties of nanopowders were evaluated. The polyvinylpyrrolidone additions significantly modify the powders morphology providing the formation of numerous pores and enhancing the photocatalytic activity of obtained materials. The kinetics of Chicago Sky Blue diazo dye adsorption from the aqueous solutions on the surface of obtained materials can be described as the pseudo-first order so as the pseudo-second order kinetic models. The kinetics of photocatalytic dye decomposition are described by the Langmuir-Hinshelwood model. Porous SiO2 powders containing different structural defects demonstrate photocatalytic activity under UV irradiation. The rate of the photocatalytic dye decomposition decreases with the increase of SiO2 content in ZnO-SiO2 photocatalysts. The high constant rate (0.024 min(-1)) is observed with the application of porous 4ZnO-SiO2 photocatalyst. It was found that structural defects play the important role in luminescent and photocatalytic characteristics of prepared materials. The input of the defect-relative effect into the total photocatalytic activity of ZnO-SiO2 nanocomposites is remarkable (up to 30 %).