Single-atom catalyst is selective activation of oxidants in catalyzing persulfate-based Fenton-like reactions: Pivotal role of distinct active sites

Peroxymonosulfate (PMS) and peroxydisulfate (PDS) are two oxidants in single-atom catalysts (SACs) catalyzed persulfate-based Fenton-like reactions for organics degradation. A SAC with the specific active site may elicit varied responses with PMS and PDS due to their distinct chemical structures, leading to significantly different activation capacities. Therefore, identifying oxidant type−activation capacity correlations in SACs activated persulfate reactions is essential for maximizing their catalytic capacity. Here, a Co SAC (Co-N-C) containing Co-N₄ active sites and its corresponding metal-free catalyst counterpart (N-C) are synthesized to activate PMS and PDS for tetracycline (TC, as an indicative organic) degradation. The rates of TC degradation in four systems are Co-N-C/PMS (0.573 min-1) > Co-N-C/PDS (0.190 min-1) ≈ N-C/PDS (0.186 min-1) > N-C/PMS (0.042 min-1), proving that Co-N-C is selective for oxidants and PMS is a more efficient candidate. Singlet oxygen is unveiled to be almost the sole reactive specie in four systems. Experiments and theoretical analyses demonstrate that the Co single-atom of Co-N-C serves as the active site for PMS activation while the nitrogen rather than the Co single-atom of Co-N-C is responsible for PDS activation, which induces the significant performance disparity between Co-N-C and N-C in activating PMS and the nearly identical performance in activating PDS.