Synergistic effect of adsorptive photocatalytic oxidation and degradation mechanism of cyanides and Cu/Zn complexes over TiO2/ZSM-5 in real wastewater.

The treatment of cyanide wastewater from the gold industry is essential. Photocatalytic oxidation is an effective method for the elimination of cyanides and metal cyanide complexes. TiO2/ZSM-5 composite photocatalysts with different SiO2/Al2O3 ratios were prepared using the solid-state dispersion (SSD) method. The composite catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The catalytic efficiency of different SiO2/Al2O3 ratios and the synergistic effect of adsorptive photocatalytic oxidation for the degradation of cyanide wastewater was investigated under different adsorption and illumination times. With the extension of the photocatalytic time (>2.0 h), the composite catalyst with a high SiO2/Al2O3 ratio had better photocatalytic performance. A 93.97% degradation efficiency of total cyanides was observed after adsorption for 3.0 h and illumination for 4.0 h under room temperature with air as the oxidant. The removal efficiencies of the copper and zinc ions were 81.67% and 100%, respectively. The degradation of cyanide followed pseudo-first-order kinetics. Energy dispersive spectroscopy (EDS) results showed that the generally irregular surface of the catalyst with a high SiO2/Al2O3 ratio contains more nano-TiO2. The adsorption capacities of copper and zinc were relatively high. X-ray photoelectron spectroscopy (XPS) suggested that cyanide was eventually degraded to CO2 and NO3-. Copper and zinc were removed in the form of Cu(II) and Zn(II).