Construction of Li/K dopants and cyano defects in graphitic carbon nitride for highly efficient peroxymonosulfate activation towards organic contaminants degradation.

As an emerging peroxymonosulfate (PMS) activation catalyst, graphitic carbon nitride (g-C3N4) is non-toxic and eco-friendly, while its poor catalytic performance hinders the application of pristine g-C3N4. Herein, a simple LiCl/KCl molten salts-assisted thermal polymerization method was adopted to promote the photocatalytic performance of g-C3N4. With the insertion of Li/K dopants and the introduction of surface cyano defects, the modified catalyst exhibited greatly enhanced ability on PMS activation towards acetaminophen removal, observing a 13 times higher rate constant than pristine g-C3N4 (k = 0.0435 min-1 vs. 0.0033 min-1). The main reactive oxygen species for pollutant degradation were identified as sulfate radicals and singlet oxygen. The wavefunction analysis at excited states based on density functional theory suggests that the introduction of cyano defects greatly promotes the separation of photo-generated electron-hole pairs, thereby achieving higher photocatalytic efficiency. In addition, the doping of Li/K significantly enhances the interaction between PMS and the catalyst surface, and orients the electron transfer from PMS to catalyst to generate non-radical species singlet oxygen, which improves the catalyst resistance to anions-containing water matrices.