Solar-driven CO₂ conversion over Co²⁺ doped 0D/2D TiO₂/g-C₃N₄ heterostructure: Insights into the role of Co²⁺ and cocatalyst

Low charge separation efficiency is the critical limitation for solar-driven CO₂ conversion into chemicals fuels. Accelerating charge transfer in the interface of photocatalysts is an intriguing approach to suppress charge recombination. Herein, Co²⁺ doped 0D/2D TiO₂ quantum dots confined in graphitic carbon nitride (CoTiCN) heterostructure was prepared by in-situ pyrolysis of MOFs and urea. Co²⁺ serves as the bridge of linking 0D TiO₂ and 2D g-C₃N₄ in the interface, and consequently accelerates charge transfer in the interface from 2D g-C₃N₄ to 0D TiO₂. As a result, CO evolution rate for photocatalytic CO₂ reduction reached 290 μmol g^-1 h^-1, much higher than those of pure g-C₃N₄ and TiO₂/g-C₃N₄. In addition, photocatalytic mechanism study indicates that [Co(bpy)₃]Cl₂ in the system functions as cocatalyst without any photocatalytic activity under visible light irradiation. Electron transfer occurs from heterogeneous photocatalyst to [Co(bpy)₃]Cl₂, which acts as the electron transporter as active sites to catalyze CO₂ reduction into CO. This work provides an insight into the design of metal doped 0D/2D material towards visible light driven CO₂ reduction from the viewpoint of promoting charge transfer in the interface and the understanding of the photocatalytic mechanism of cocatalyst in system.