Photosynthesis of Au/TiO2 nanoparticles for photocatalytic gold recovery from industrial gold-cyanide plating wastewater

A series of Au_x/TiO₂ nanoparticles (NPs) with different gold loadings (x = 0.1–1.0 wt%) was synthesized by the photodeposition and then employed as photocatalysts to recover precious component from the industrial gold-cyanide plating wastewater. Effects of Au loading, catalyst dosage and types of hole scavenger on the photocatalytic gold recovery were investigated under ultraviolet–visible (UV–Vis) light irradiation at room temperature. It was found that different Au loadings tuned the light absorption capacity of the synthesized photocatalysts and enhanced the photocatalytic activity in comparison with the bare TiO₂ NPs. The addition of CH₃OH, C₂H₅OH, C₃H₈O, and Na₂S₂O₃ as a hole scavenger significantly promoted the photocatalytic activity of the gold recovery, while the H₂O₂ did not. Among different hole scavengers employed in this work, the CH₃OH exhibited the highest capability to promote the photocatalytic gold recovery. In summary, the Au_0.5/TiO₂ NPs exhibited the best photocatalytic activity to completely recover gold ions within 30 min at the catalyst dosage of 0.5 g/L, light intensity of 3.20 mW/cm² in the presence of 20 vol% CH₃OH as hole scavenger. The photocatalytic activity slightly decreased after the 5th cycle of recovery process, indicating its high reusability.