Rational construction of half-metallic carbon nitride and TiO2 S-scheme heterojunction for efficient photocatalytic CO2 reduction

Photocatalytic CO 2 reduction to high-value chemicals is an effective route to address energy and environmental issues. However, it remains challenging to develop semiconductor photocatalysts with high activity and efficient charge separation. Herein, a novel hm-C 4 N 3 /TiO 2 S-scheme heterojunction was synthesized, and its interfacial charge transfer mechanism was revealed by in-situ XPS, KPFM and the density functional theory calculations. The construction of the S-scheme heterojunction establishes a strong internal electric field (IEF), which significantly accelerates the separation and directional migration of photogenerated carriers and boosts the reaction kinetics. The optimized photocatalyst delivers a CO production rate of 15.20 μmol g −1 h −1 , about 5 times that of pure TiO 2 . Gibbs free energy calculations confirm that the heterojunction reduces the reaction energy barrier and provides a thermodynamic advantage for CO 2 to CO conversion. This study offers a feasible strategy for designing half-metallic carbon nitride-based S-scheme heterojunctions toward efficient photocatalytic CO 2 reduction.