Regulating nitrogen vacancies within graphitic carbon nitride to boost photocatalytic hydrogen peroxide production

Introducing nitrogen vacancies is an effective method to improve the catalytic performance of g-C3N4-based photocatalysts, whereas understanding how nitrogen vacancies types affect the catalytic performance remains unclear. Herein, two different types of nitrogen vacancies were successfully introduced into g-C3N4 by pyrolysis of melamine under argon and ammonia atmosphere with subsequent HNO3 oxidation. The pyrolysis atmosphere is found to have a significant influence on the introduced nitrogen vacancies type, where tertiary nitrogen groups (N3C) and sp(2)-hybridized nitrogen atoms (N2C) were the preferred sites for the formation of nitrogen vacancies under ammonia and argon pyrolysis, respectively. Moreover, nitrogen vacancies from N3C are experimentally and theoretically demonstrated to facilitate the narrowed band gap and the improved oxygen absorption capability. As expected, the optimal catalyst exhibits high H2O2 yield of 451.8 mu M, which is 3.8 times higher than the pristine g-C3N4 (119.0 mu M) after 4 h and good stability after10 photocatalytic runs.