Study on Method and Mechanism of Noble Metals Photoelectric Deposition by Directly Utilizing Solar Energy

The recovery of noble metals is crucial in terms of resource utilization and ecological environment. Herein, a green strategy for the recovery of three noble metals, Au, Ag, and Pt, by photoelectric deposition at the cathode without external voltage is described. The realizability and mechanism of noble metals deposition are investigated and analyzed in terms of the band structure and the reduction potential of metal ions using the special heterostructure ZnO/ZnS composites derived from metal–organic frameworks, as well as ZnO and Fe2O3 semiconductors. It is found that ZnO/ZnS has preferable photoelectrochemical performance than pure ZnO due to their effective electron–hole separation and appropriate band matching structure. To deposit metals Au, Ag, and Pt, the potential of electrons in the conduction band of ZnO/ZnS should be more negative than the reduction potential of these metals, allowing for the deposition of these metals while simultaneously undergoing an oxygen evolution reaction, mediated by the photogenerated holes on the surface of the photoanode, and the collection of conduction band electrons by the back electrode.