Catalytic activity and reaction mechanisms of single-atom metals anchored on nitrogen-doped carbons for peroxymonosulfate activation

Single-atom catalysts have attracted tremendous interests in peroxymonosulfate (PMS)-based advanced oxidation processes due to their maximum atom utilization and high reactivity, however the role of nitrogen-coordinated metal (MNx) sites with different metal centers remain blurred. Herein, a series of single-atom metals anchored on nitrogen-doped carbons (denoted as M-N/C, M = Fe, Co, Cu, and Mn) using zeolitic imidazolate frameworks as precursors are constructed for PMS activation. Their catalytic activity order follows Fe > Co > undoped N/C > Cu > Mn, especially the degradation rates of the eight model pollutants for Fe-N/C and Co-N/C are 2.5-22.4 and 1.5-19.5 times higher than those for undoped N/C, respectively. Moreover, the nature of catalytic metal center can govern the degradation behaviors in the coexisting water constituents. Experimental and theoretical results reveal that singlet oxygen (O-1(2)) is the main oxidant responsible for pollutant degradation and its evolution path over FeN4 or CoN4 sites (PMS.OH*.*O -> O-1(2)) is elucidated, between which FeN4 with lower energy barrier is more conducive to O-1(2) generation. This study can not only provide guidance for the development of highly active atomic M-N/C catalysts, but also lead to a better molecular-level understanding of PMS activation mechanism over MN4 sites.

Automated summary

Single-atom catalysts with different metal centers anchored on nitrogen-doped carbons were constructed for peroxymonosulfate (PMS) activation. The catalytic activity order is Fe > Co > undoped N/C > Cu > Mn, with Fe-N/C and Co-N/C showing significantly higher degradation rates of model pollutants compared to undoped N/C. Singlet oxygen (O-1(2)) was identified as the main oxidant responsible for pollutant degradation, and FeN4 was found to be more conducive to O-1(2) generation than CoN4.