Abstract: Photocatalytic CO₂ reduction is a promising solution for alleviating the energy crisis and mitigating environmental problems. In this work, a progressive chemical reduction strategy was innovatively used to achieve defect site reconstruction on TiO₂ with a predesigned fluorine-mediated TiOF₂/TiO₂ heterostructure as the precursor. The low-coordinate Ti sites can facilitate the adsorption of CO₂, effectively activate the 2π orbitals of CO₂, break the C=O bond of CO₂, and decrease the energy barrier for *COOH generation, which greatly improves the efficiency of photocatalytic CO₂ reduction. This system demonstrates 100% selectivity in converting CO₂ to CO with H₂O as the electron donor under visible light irradiation. Moreover, the adsorption/activation of CO₂ and CO desorption at various defect sites on the TiO₂ surface and the reaction mechanism of photocatalytic CO₂ reduction to CO were systematically revealed. This work lays the groundwork for designing controllable surface defect active sites suitable for photocatalytic CO₂ reduction.

Key words: Photocatalytic CO₂ reduction, Fluoride-mediated heterostructure, TiO₂, Defect, Active sites