Improved H2O2 photogeneration by KOH-doped g-C3N4 under visible light irradiation due to synergistic effect of N defects and K modification

KOH-doped graphitic carbon nitride (g-C3N4) prepared by thermal copolymerization in the presence of KOH was used for photogeneration of H2O2 under visible light irradiation. The H2O2 yield of the KOH-doped g-C3N4 photocatalyst with isopropanol (IPA) as a scavenger was 704 mu M.g(g-C3N4)(-1).h(-1), twelve times that of unmodified g-C3N4. The total H2O2 output with IPA as a scavenger increased to 86.08 mM after 60 h. The photogeneration of H2O2 with g-C3N4 occurred as two single-electron reactions in which oxygen was reduced to the superoxide radical by one photogenerated electron and further reduced to H2O2 by reacting with another electron and two protons released by oxidization of IPA by holes. KOH doping had a synergistic effect owing to the strong electron-withdrawing ability of N defects caused by N vacancies and cyano groups, and enhanced electron transport due to K bridges between the C3N4 layers. These effects significantly enhanced the H2O2 photogeneration performance of g-C3N4 by improving the quantum efficiency, narrowing the band gap, strengthening IPA adsorption on g-C3N4, and lowering the energy barrier of the oxygen reduction reaction. This work provides an attractive and promising strategy for green H2O2 production.