Phase-Selective Disordered Anatase/Ordered Rutile Interface System for Visible-Light-Driven, Metal-Free CO₂ Reduction

Abstract

Visible-light-driven photocatalytic CO₂ reduction using TiO₂ that can absorb light of all wavelengths has been sought for over half a century. Herein, we report a phase-selective disordered anatase/ordered rutile interface system for visible-light-driven, metal-free CO₂ reduction using a narrow band structure, whose conduction band position matches well with the reduction potential of CO₂ to CH₄ and CO. A mixed disordered anatase/ordered rutile (A_d/R_o) TiO₂ was prepared from anatase and rutile phase-mixed P25 TiO₂ at room temperature and under an ambient atmosphere in sodium alkyl amine solutions. The A_d/R_o TiO₂ showed a narrow band structure due to multi-internal energy band gaps of Ti³⁺ defect sites in the disordered anatase phase, leading to high visible light absorption and simultaneously providing fast charge separation through the crystalline rutile phase, which was faster than that of pristine P25 TiO₂. The band gap of A_d/R_o TiO₂ is 2.62 eV with a conduction band of -0.27 eV, which matches well with the reduction potential of -0.24 V_NHE of CO₂/CH₄, leading to effective electron transfer to CO₂. As a result, the A_d/R_o TiO₂ provided the highest CH₄ production (3.983 μmol/(g h)), which is higher than that of even metal (W, Ru, Ag, and Pt)-doped P25, for CO₂ reduction under visible light.