Effect of Cu valence states on conduction band position and reduction selectivity of TiO2-based heterojunction photocatalysts

TiO₂ has low photocatalytic activity due to its easy recombination of photogenerated charges and low visible light utilization efficiency. This study utilized the keto-enol tautomerism principle of fructose in an alkaline environment to successfully obtain Cu₂O/TiO₂ (CT), Cu₂O/TiO₂/Cu (CTC), and TiO₂/Cu (TC) catalysts. As Cu(I) transformed into Cu(0), the bandgap narrowed, significantly enhancing visible light absorption. Photocatalytic tests showed that CT-0.15 exhibited the highest hydrogen production rate (279.53 μmol g^-1 h^-1), which was 25.18 times higher than that of TC-2. However, CTC-1 had the highest CO production rate (10.58 μmol g^-1 h^-1). Optoelectronic test revealed that CT-0.15 and CTC-1 had higher separation efficiency of photogenerated exciton. Density functional theory (DFT) calculations indicated that the change in the valence state of Cu influenced the reaction mechanism, with CT being favorable for the adsorption of H⁺ in HER and CTC promoting the adsorption of CO₂ in carbon dioxide reduction reaction (CO2RR).