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 (Ad/Ro) 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 Ad/Ro 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 Ad/Ro TiO2 is 2.62 eV with a conduction band of -0.27 eV, which matches well with the reduction potential of -0.24 VNHE of CO2/CH4, leading to effective electron transfer to CO2. As a result, the Ad/Ro 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.
Keywords: disordered anatase-only TiO2; metal free; narrow band structure; oxygen vacancy; visible-light-driven CO2 reduction.