Cu/TiO2 Photocatalysts for CO2 Reduction: Structure and Evolution of the Cocatalyst Active Form.

Extensive work on a Cu-modified TiO₂ photocatalyst for CO₂ reduction under visible light irradiation was conducted. The structure of the copper cocatalyst was established using UV–vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. It was found that copper exists in different states (Cu⁰, Cu⁺, and Cu²⁺), the content of which depends on the TiO₂ calcination temperature and copper loading. The optimum composition of the cocatalyst has a photocatalyst based on TiO₂ calcined at 700 °C and modified with 5 wt% copper, the activity of which is 22 µmol/(h·g_cat) (409 nm). Analysis of the photocatalysts after the photocatalytic reaction disclosed that the copper metal on the surface of the calcined TiO₂ was gradually converted into Cu₂O during the photocatalytic reaction. Meanwhile, the metallic copper on the surface of the noncalcined TiO₂ did not undergo any transformation during the reaction. [ABSTRACT FROM AUTHOR]