Structural design of SiO2/TiO2 materials and their adsorption-photocatalytic activities and mechanism of treating cyanide wastewater

Cyanide wastewater contains free cyanide and metal-cyanide complexes, which need to be treated before they are discharged. In this study, we synthesized a mesoporous SiO2/TiO2 material, and used it to treat cyanide wastewater by an adsorption-photocatalytic oxidation synergistic method. The effects of material structure and TiO2 loading method on the removal efficiencies of cyanide, copper and zinc were investigated. The experiments proved that the gel-sol method was more effective, and the kinetic and thermodynamic analysis of dark adsorption process was performed. The results indicated that the dark adsorption kinetics conformed to the pseudo second order, and the thermodynamics indicated that it was an endothermic process. The experimental data stated clearly that the degradation efficiency of total cyanide reached 95.98% and the removal efficiencies of copper and zinc reached 92.70% and 98.69% under the conditions of dark adsorption for 0.5 h and photocatalysis for 4.0 h, respectively. The cyanide was chemisorbed on the material surface. XPS, XRD analysis indicated that cyanide was finally decomposed into NO3− and CO2; copper and zinc were removed in the form of CuO, Cu2O, ZnO.