Hybrid Cu_xO–TiO₂ Nanopowders Prepared by Ball Milling for Solar Energy Conversion and Visible-Light-Induced Wastewater Treatment

Hybrid nanocomposites of Cu2O–(R)TiO2, CuO–(R)TiO2, and Cu3TiO4–(R)TiO2 (where R represents the rutile phase of TiO2) nanopowders (NPs) were produced via solid state reaction followed by 20 h of ball milling; their photocatalytic activities were evaluated for methylene blue (MB) degradation under visible light intensity (∼65 mW/cm2) and compared to Degussa P25 under both ultraviolet (UV) and visible light irradiations. The highest MB degradation rate under the visible light irradiation was observed to be 0.271 ± 0.010 h–1 for Cu2O–(R)TiO2 NPs, which was 2.5 times higher than that of P25, while under UV illumination both the Cu2O–(R)TiO2 and Cu3TiO4–(R)TiO2 NPs were slightly less active than that of the P25, and CuO–(R)TiO2 was the least active among all. The solar energy conversion performance of the CuxO–(R)TiO2 NPs was observed to be controlled by the applied potentials. The highest stable cathodic photocurrent density (6.3 μA/cm2) was observed for Cu2O–(R)TiO2 NPs at a low negative bias voltage (−0.3 V vs Ag/AgCl, 3 M KCl) and under the solar simulator (AM 1.5G). This method to design multifunctional visible-light-active metal oxides is simple and scalable and has the potential to prepare other efficient photocatalysts for solar energy conversion.