H2O2 Assisted Photoelectrocatalytic Oxidation of Ag-Cyanide Complexes at Metal-free g‑C3N4 Photoanode with Simultaneous Ag Recovery

A g-C3N4 thin film was synthesized by a liquid-based reaction onto ITO substrate via the calcination treatment. The resultant electrode was used as photoanode for photoelectrocatalytic (PEC) oxidation of Ag cyanide complexes with simultaneous Ag recovery, which was enhanced with the addition of H2O2. Surface variation of the g-C3N4 photoanode and titanium cathode was analyzed using SEM, XRD, and XPS techniques. It was observed that, with the cyanide oxidation, Ag oxides and metal Ag were deposited onto the g-C3N4 photoanode and titanium cathode, respectively. The photoelectrochemical response of the g-C3N4 photoanode was obviously increased after the AgO deposition. ESR and trapping experiments confirmed the existence and roles of •O2 – and •OH in the PEC oxidation process. The photogenerated electrons from g-C3N4 could be captured by •O2 – and H2O2, generating •OH radicals for oxidizing the Ag cyanide complexes. Meanwhile, the deposition of AgO species onto the g-C3N4 surface increased its electrical conductivity and the migration rate of the photogenerated electrons. Deposited AgO can also enhance the production of active radicals, leading to an increased PEC activity toward the cyanide destruction.