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

•Photoelectro-oxidation of diclofenac was largely enhanced with persulfate addition.•Cu2O was identified at copper cathode by in situ Raman technique.•Activation mechanism of persulfate to SO4− at copper cathode was proposed.

In this work, persulfate (S2O82−, PS) was introduced to the photoelectrocatalytic (PEC) system, which consisted of a γ-Bi2MoO6 photoanode and a copper foil cathode (Bi2MoO6/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 SO4− 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 Cu2O formed on the surface in the reaction process with the S2O82− 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.

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