Recovery of silver metal from low concentrated wastewater by photocatalysis

This work studies the photocatalytic activity of zinc oxide (ZnO) nanopowder to recover silver (Ag) metal from low Ag⁺ concentrated solution under artificial ultraviolet (UV) light. Benchmark titanium dioxide (P25 TiO₂) was used for comparison purpose. Experimental results indicated that ZnO exhibited superior performance for Ag recovery compared to TiO₂. Under optimal catalyst loading, the achieved Ag removal efficiencies were 100% and 99.94% at 0.2 g/L ZnO (1 h) and 2 g/L TiO₂ (2 h), respectively. An induction period at low concentration of TiO₂ (0.1 g/L) was observed and a mechanism was proposed. The photodissolution of ZnO was assessed and proved to be negligible. Recovered pure Ag metal was characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM), showing a promising effective Ag recovery technology using ZnO photocatalyst.