Engineering Triune Active Sites on Alkali Metal-Doped Graphite Carbon Nitride for Aqueous Catalytic Ozonation

Novel alkali metal-doped graphite carbon nitride (CN) catalysts (CN-M, where M = K, Na, or Li) with triune active sites (alkali metal atoms, cyano groups, and N vacancies) prepared by one-step pyrolysis to enhance the catalytic ozonation performance of pristine CN. The structural analysis of CN-M and the significant enhancement adsorption of ozone performance are demonstrated by density functional theory calculations and experiment tests. The insertion of alkali atoms can shorten the distance between the layers, forming an electronic bridge and accelerating the transfer of electrons. Cyano groups serve as strong electron-withdrawing groups that effectively modulate the electronic structure of the CN surface. N vacancies ulteriorly optimize the charge distribution on the surface of the material and promote ozone adsorption. The prepared CN-Na, CN-K, and CN-Li catalysts exhibit excellent atrazine (ATZ) degradation efficiencies of 99.6%, 97.0%, and 94.0%, respectively, that greatly exceed that of CN (62.8%) and single ozone oxidation (54.8%). The toxicity results of the ATZ intermediates show a significant toxicity reduction in ATZ after the heterogeneous catalytic ozonation process. This study provides insights into the synergistic interactions of alkali metal atoms, cyano groups, and N vacancies, which will help to guide and design triune active site CN-based catalysts for enhanced ozone activation.