Photocatalytic CO2 reduction on Cu single atoms incorporated in ordered macroporous TiO2 toward tunable products

Abstract

The photocatalytic conversion of CO₂ to hydrocarbons is a fascinating strategy to defuse the growing energy and environmental dilemmas, but there are great challenges in improving photocatalytic efficiency and tuning product selectivity. Both are of equal importance to increase the yield of the desired product and clarify the photocatalytic CO₂ reduction mechanism. Herein, a Cu single-atom-incorporated three-dimensional-ordered macroporous TiO₂ (Cu_0.01/3DOM-TiO₂) photocatalyst was synthesized using a template-assisted in situ pyrolysis method. The Cu single atoms are uniformly anchored in a 3DOM TiO₂ matrix, which not only broadens the light absorption range but also provides specific active sites for the adsorption and transformation of CO₂ molecules. The photocatalytic CO₂ reduction reaction was conducted in gas–solid and liquid–solid systems, respectively, to explore the effects of reaction modes on the CO₂ conversion efficiency and product selectivity. The results indicate that the photocatalytic CO₂ reduction reaction in gas–solid system mainly produces methane (CH₄), with a high selectivity of 83.3% and a formation rate of 43.15 μmol g⁻¹ h⁻¹. In contrast, the main product in the liquid–solid system is ethylene (C₂H₄), with a selectivity of 58.4% and a formation rate of 6.99 μmol g⁻¹ h⁻¹. The Cu_0.01/3DOM-TiO₂ photocatalyst shows superior activity and selectivity in the gas–solid system while favorably producing C₂H₄ in the liquid–solid system. The possible photocatalytic mechanisms of CO₂ reduction in the two different reaction systems are discussed according to in situ infrared spectroscopy. This work provides some new information on promoting photocatalytic CO₂ reduction to desirable products by the rational design of photocatalysts as well as tuning the reaction conditions.