Carbon vacancies in porous g-C3N4 nanosheets induced robust H2O2 production for highly efficient photocatalysis-self-Fenton system for metronidazole degradation

In this paper, porous g-C3N4 nanosheets with carbon vacancies (Cv-PCNNS) are developed for the photocatalysis-self-Fenton system for efficient metronidazole degradation without the addition of H2O2. These Cv-PCNNS are produced through the thermal polymerization of urea and subsequent heat treatment in Ar. The carbon vacancies are characterized by X-ray photoelectron spectroscopy, elemental analyzer, etc. Carbon vacancies in the Cv-PCNNS accelerate not only photo-induced charge separation but also improve O2 activation. Meanwhile, based on DFT calculations, the amino groups surrounding C vacancies provide H for photocatalytic O2 reduction to H2O2 and capture H from the surroundings to restore its original appearance. The H2O2 production rate formed by the O2 one-step dual-electron reduction reaction caused by the introduction of C vacancies reached 984.8 mu mol L-1 h-1 under optimum conditions, which is 10 times higher than the original bulk g-C3N4. The metronidazole degradation rate is increased to 90.7% within 100 min, and the removal rate is higher than conventional Fenton technology by utilizing the cascade mode in the photocatalysis-self-Fenton reaction. This novel and viable route for efficient metronidazole degradation will be beneficial to other organic pollutants degradation in actual applications.