Defect structures of semiconductors intrinsically regulate the trap states, excitons and active charge carriers for artificial photosynthesis systems. A g-C3N4 system with abundant nitrogen defects was prepared through a thermal polycondensation strategy to reveal the role of trap states and exhibited a 20-fold enhanced H2 evolution efficiency relative to bulk g-C3N4 under visible light irradiation. Subsequent femtosecond transient absorption spectroscopy study found that the N-defect induced shallow trap states can capture photogenerated electrons to inhibit deep trapping and direct recombination of photogenerated charges. The active electrons in shallow trap states can enhance the photocatalytic H2 evolution when compared with the inactive electrons in deep trap states. Mid-infrared transient absorption spectroscopy also confirmed the increased quantity of shallow-trapped electrons without interference of other signals. This work provides new insights for steering depth of trap states and photocatalytic processes through N defects to achieve high photocatalytic performance using femtosecond transient absorption spectroscopy.

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