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

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.