Insight into the Effect of the Cl 3p Orbital on g-C₃N₄ Mimicking Photosynthesis under CO₂ Reduction

Achieving high-efficiency photocatalytic materials to convert CO₂ into high-value chemicals is still challenging. Herein, chlorine-doped g-C₃N₄ photocatalysts (Cl-CN) were successfully synthesized by a simple multiple calcination method. The as-prepared Cl-CN exhibited satisfactory photocatalytic activity in photoreduction of CO₂. The CO yield of Cl-CN was about 39.89 μmol/g. The DRS, UPS, and VB-XPS results indicated a narrower band gap, and the negatively shifted CB potential enhanced the CO₂ reduction ability. DFT calculations and the partial density of states revealed that the Cl 3p orbital greatly contributed to the CBM and VBM of Cl-CN, which caused the narrower band gap and an upshift of the conduction band by 0.14 eV over that of bulk-CN. The CO₂ conversion intermediate was investigated by in situ Fourier transform infrared spectroscopy, and the corresponding reaction mechanism was proposed according to the density functional theory calculations and experimental results, which showed that Cl doping and the C–Cl bond increased the photogenerated carrier lifetime and the CO₂ adsorption capacity of Cl-CN. Therefore, this work provides a deeper understanding of the effect of Cl doping on the g-C₃N₄ electronic structure and its CO₂ reduction activity.