Activity and mechanism of macroporous carbon/nano-TiO2 composite photocatalyst for treatment of cyanide wastewater

Abstract

Photocatalytic oxidation can effectively treat cyanide wastewater generated from cyanide plating and gold cyanidation extraction process. In this study, monodisperse SiO2 microspheres were prepared by stober method, and macroporous carbon was prepared by template method with SiO2 as template and sucrose as carbon source, and the macroporous carbon/nano-TiO2 composite photocatalyst were prepared by solid-phase dispersion method. The material was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD)，UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence (PL), energy spectrometry (EDS), N2 adsorption–desorption test, thermogravimetric analysis (TGA), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The results show that the material has a large specific surface area, excellent pore structure, and light absorption properties. The photocatalytic treatment of cyanide wastewater was carried out by changing variables such as the loading amount of nano-TiO2, light wavelength, and catalyst dosage. The data showed that when the loading amount of nano-TiO2 was 15 wt% and the catalyst dosage was 3 g/L, the degradation efficiency of total cyanide was 98.10% and the removal efficiency of copper and zinc ions were 99.56% and 100%, respectively, after adsorption in cyanide wastewater for 0.5 h and then light illumination under high-pressure mercury lamp for 3 h (air is introduced during this period). Based on the EDS and XPS analyses, macroporous carbon/nano-TiO2 material will decompose Cu(CN)32- and Zn(CN)42- in cyanide wastewater to Cu+, Zn2+ and •CN. Cu+, •CN and CN－ are further oxidized to Cu2+ and CNO－, Cu2+ and Zn2+ will be removed by being adsorbed to the material surface, and CNO－ will be further degraded to carbon oxides (COX) and nitrogen oxides (NOX).