DFT Study on Sulfur-Doped g-C 3 N 4 Nanosheets as a Photocatalyst for CO 2 Reduction Reaction

Graphitic carbon nitride (g-C 3 N 4 ) can be used as a photocatalyst to reduce CO 2 . Doping is an efficient strategy for improving the photocatalytic activity and tuning the electronic structure of g-C 3 N 4 . The sulfur-doped g-C 3 N 4 (S-doped g-C 3 N 4 ) as a promising photocatalyst for CO 2 reduction was investigated by density functional theory methods. The electronic and optical properties indicate that doping S enhances the catalytic performance of g-C 3 N 4 . From the reduction Gibbs free energies, the optimal path for CO 2 reduction reaction to CH 3 OH production catalyzed by S-doped g-C 3 N 4 is CO 2 → COOH* → CO → HCO* → HCHO → CH 3 O* → CH 3 OH. In comparison with g-C 3 N 4, doping S can alter the rate-determining step and reduce the Gibbs free energy from 1.43 to 1.15 eV. CO 2 reduction activity of S-doped g-C 3 N 4 is better than that of g-C 3 N 4, which is in well agreement with the experimental results. Our work provides useful insights into designing nonmetal-doped g-C 3 N 4 for photocatalytic CO 2 reduction reactions.