The structure-dependent mechanism of single-atom cobalt on macroporous carbon nitride in (photo-)Fenton-like reactions

Single-atom catalysts have been believed to be ideal materials for achieving maximum utilization of metal active sites in Fenton-like catalysis for eliminating organic pollutants. However, the relationship between the single-atom structure and catalytic activity remains largely uninvestigated. Herein, a spatial confinement strategy to anchor Co single atoms (0.6-10.2 wt%) on macroporous carbon nitride (MCN) was developed, and the single atom catalysts were tested in peroxymonosulfate activation for (photo-)Fenton-like reactions. Single-atom Co-MCN was discovered to show different molecular structures, and a light-dependent mechanism in Fenton-like catalysis was revealed. Co atoms in Co-N-4 configuration present Co-N1+3/Co-N2+2 geometric structures, dependent on a Co load. Co-N1+3 is thermodynamically favorable to form, serving as the main active site. Co-N2+2 possesses an inferior catalytic activity and induces negative effects on the adjacent Co-N1+3 site. Moreover, experimental and theoretical investigations reveal a 100% nonradical reaction pathway that can be photo-switched to a nonradical/radical process by visible light. This work enriches the fundamentals of single-atom catalysis by providing new insights into the atomic metal structure, reaction pathways and mechanisms, and structure-activity relationships in organic degradation.