Enhanced CO2 photoreduction activity of black TiO2−coated Cu nanoparticles under visible light irradiation: Role of metallic Cu

Abstract Nanosized metallic copper could be a replacement of noble metals for improving photoactivity of TiO2-based photocatalysts, but it tends to be oxidized by oxygen in surroundings. To avoid this, black TiO2−coated Cu nanoparticles (denoted as Cu@TiO2) were constructed in the present work, and their photoactivity for the photoreaction of CO2 with H2O vapor under visible-light irradiation was explored. X-ray diffraction, transmission electron microscopy and selected area electron diffraction analysis for the used Cu@TiO2 confirm the hierarchical structure of Cu@TiO2 and oxygen resistance of metallic Cu. The photocatalytic activity for Cu@TiO2 (∼4%Cu) reaches 1.7 times of that for its counterpart, bared black TiO2. The improved photoactivity is attributed to the embedded metallic Cu, which promotes the formation of oxygen vacancies in TiO2 through the metal-oxide interaction, thus increasing the visible-light absorption of Cu@TiO2 and the adsorption of CO2 on their surface. Furthermore, the metallic Cu increases photoinduced charge-separation of TiO2 through trapping electrons as evidenced by transient photocurrent measurements. The present work sheds light on developing new type of metal-oxide based visible-light-driven photocatalysts.