Enhancement of photoelectrocatalytic degradation of diclofenac with persulfate activated by Cu cathode

In this work, persulfate (S 2 O 8 2− , PS) was introduced to the photoelectrocatalytic (PEC) system, which consisted of a γ-Bi 2 MoO 6 photoanode and a copper foil cathode (Bi 2 MoO 6 /Cu/PEC/PS system). Significant enhancement of diclofenac sodium (DCF) degradation efficiency was observed in this system under visible light irradiation. At an applied bias of 1.5   V and initial solution pH of 5.62, the removal efficiency of DCF with an initial concentration of 10   mg/L was increased from 19.4% in the PEC process to 86.3% in the PEC process with 10   mM   PS addition. The pseudo-first-order kinetic rate constant of DCF degradation was increased from 0.1112   h −1 to 1.0498   h −1 . Active free radicals involving SO 4 − and HO were produced in this process, which were confirmed by electron spin resonance analysis. Furthermore, the surface variation of copper foil cathode was characterized by FE-SEM, GI-XRD, XPS and in situ Raman spectroscopy. It was demonstrated that Cu 2 O formed on the surface in the reaction process with the S 2 O 8 2− addition, which was further confirmed by the photoelectrochemical analysis of the cathode. The surface Cu(0)–Cu(I)–Cu(II)–Cu(0) redox cycle of cathode was proposed, which was responsible for the persulfate activation, leading to the generation of free radicals. This work may provide a new perspective on the combined utilization of different technologies for catalytic contaminant removal.