Microwave assisted synthesis of ZnO-TiO₂ and its visible light catalytic denitrification activity

Comparing the composite TiO₂ prepared by hydrothermal sol gel method and microwave-assisted sol gel method, the microwave-assisted sol gel method with shorter time and better crystallinity was finally used to prepare ZnO-TiO₂ materials with different composite ratios. The specific surface area, pore volume and pore size of ZnO- TiO₂ composite are significantly larger than those of TiO₂. The surface acidity of ZnO-TiO₂ composite is stronger. The band structure is conducive to the efficient separation of electrons and holes, and the catalytic reduction activity and selectivity are stronger. The best composite ratio of ZnO and TiO₂ is optimized to be 0.2 through photocatalytic denitration experiments. For NO_x with an initial concentration of 6.83 mg/m³, under the light source condition irradiated by 65 W energy-saving lamp, the visible photocatalytic removal efficiency is as high as 85%. When the NO_x concentration is increased to 13.67 mg/m³ and the ammonia nitrogen ratio is 1∶1, the denitration efficiency is as high as 96%, which is 43% higher than that of pure TiO₂. According to mechanism analysis, the whole reaction can be divided into adsorption and photocatalysis. Adsorption is the speed control step of the reaction. NO is oxidized to NO₂ under the action of adsorbed oxygen, and photogenerated electrons can further reduce NO₂ to N₂. After NH₃ is introduced, NH₃ and photogenerated electrons work together to improve NO_x removal efficiency.