Enhanced Visible-Light Photoactivity of CuWO4 through a Surface-Deposited CuO

Several papers have shown that CuWO4 is active under visible light for water oxidation at an applied potential bias and for organic degradation in an aerated aqueous suspension. In this work, we report that the observed reduction of O2 on the irradiated CuWO4 is a multielectron transfer process with the formation of H2O2. More importantly, the surface modification of CuWO4 with 1.8 wt % of CuO can increase the activity by approximately 9 times under UV light and by 5 times under visible light, for phenol degradation in aerated aqueous suspension. The catalyst was prepared by a hydrothermal reaction between Cu(NO3)2 and Na2WO4, followed by thermal treatment at 773 K. High-resolution transmission electron microscopy revealed that triclinic CuWO4 (40 nm) was covered by monoclinic CuO (4 nm). Through a combination of photo- and electrochemical measurement, a plausible mechanism responsible for the activity enhancement is proposed, involving an interfacial electron transfer from CuO to CuWO4 and an interfacial hole transfer from CuWO4 to CuO.