Carbon Doping Regulates Charge Transfer Paths via a Type-II to S-Scheme Transformation to Improve Photocatalytic Performance.

Designing S - scheme heterojunctions with enhanced interfacial interaction is an effective strategy for promoting the separation of photocarriers while maintaining strong photoredox capabilities. However, precisely tailoring the interfacial charge transport pathways between two contacted semiconductors remains a significant challenge due to the similar band alignment in type - II and S - scheme heterostructures. Herein, we report a facile and low-cost carbon doping strategy to smartly tune the charge transfer pathway via a type - II to S - scheme transformation for efficient photocatalytic H 2 evolution and H 2 O 2 synthesis. Density functional theory calculations combined with in situ XPS studies demonstrate that the Fermi level of MoO 2 shifts from being higher than that of C 3 N 4 to being lower after carbon doping, which drives the inversion of the internal electric field (IEF) direction between MoO 2 and C 3 N 4 , thus enabling a transition from type - II MoO 2 /C 3 N 4 heterojunctions to S - scheme C-MoO 2 /C 3 N 4 heterojunctions. As a result, the optimal S - scheme C-MoO 2 /C 3 N 4 heterojunctions exhibit a high H 2 evolution rate of 16.2 mmol g -1 h -1 and a H 2 O 2 production rate of 877 μmol g -1 h -1 , notably surpassing those of the original C 3 N 4 and type - II MoO 2 /C 3 N 4 heterojunctions. This work provides valuable insights into the fabrication of C 3 N 4 heterostructures and the control of electron migration pathways, thereby creating new possibilities for photocatalysis and optoelectronics applications.