Doping and defects in carbon nitride cause efficient in situ H2O2 synthesis to allow efficient photocatalytic sterilization

Abstract

In situ photocatalytic synthesis of H₂O₂ for disinfection has attracted widespread attention because it is a clean and environmentally friendly sterilization method. Graphitic carbon nitride has been used as a very selective photocatalyst for H₂O₂ generation but has some limitations (e.g., insufficient light absorption, rapid electron-hole recombination, and slow direct two-electron reduction processes) that prevent efficient H₂O₂ production. In this study, potassium-doped graphite carbon nitride with nitrogen vacancies (NDKCN) was prepared using a simple method involving a thermal fusion salt and N₂ calcination, which possessed an ultrathin nanosheet structure (1.265 nm) providing abundant active sites. Synergistic effects caused by nitrogen vacancies and K⁺ and I^- doping in the NDKCN photocatalyst gave the NDKCN a good ability to absorb light, undergo fast charge transfer, and give a high photoelectric current response. The optimized photocatalytic H₂O₂ yield of the NDKCN was 780.1 μM·g^-1·min^-1, which was 10 times the yield of the pristine g-C₃N₄. Tests involving quenching reactive species, electron spin resonance, and rotating disk electrodes indicated that one-step two-electron direct reduction on the NDKCN caused excellent H₂O₂ generation performance. The ability to efficiently generate H₂O₂ in situ gave NDKCN an excellent bactericidal performance, and 7.3 log₁₀ (colony-forming units·mL^-1) of Escherichia coli were completely eliminated within 80 min. Scanning electron microscopy images before and after sterilization indicated the changes in bacteria caused by the catalytic activity. The new g-C₃N₄-based photocatalyst and similar rationally designed photocatalysts with doping and defects offer efficient and simple in situ H₂O₂ sterilization.

Keywords: Carbon nitride; Hydrogen peroxide; Iodide-doping; N vacancies; Photocatalytic disinfection; Potassium-doping.