Electron transfer-mediated peroxymonosulfate activation through monoatomic Fe–pyridinic N4 moiety in biochar-based catalyst for electron-rich pollutants degradation in groundwater

Pollution of groundwater by electron-rich refractory organic pollutants (e-ROPs) is detrimental to ecological integrity and human health. Biochar (BC)-based single-atom Fe catalysts (Fe–SACs) triggering nonradical peroxymonosulfate (PMS) process has shown great potential in addressing this problem. Nevertheless, the successful formation and precise regulation of active sites on BC remain formidable challenges. Herein, co-pyrolysis of BC derived from shrimp shells and N-containing supramolecular organic frameworks with a hexagonal cavity structure of Fe3+–N3 (Fe–SOFs) was, for the first time, used to prepare an efficient and inexpensive BC-based Fe–SAC (Fe–MCA@SS). The Fe–N bond was successfully grafted from Fe–SOFs onto BC and subsequently transformed into monoatomic Fe–pyridinic N4. Moreover, Fe–MCA@SS successfully triggered an efficient nonradical PMS process, degrading 94.5 % of aniline (AN) within 5 min. Mediated electron transfer (MET) mechanism was primarily responsible for AN removal. MET was attributed to the following factors: the synergistic effect of the stronger chemical adsorption of PMS with an Fe atom in Fe–pyridinic N4 active sites, the higher redox potential of [Fe–MCA@SS/PMS]*, and the value of the lowest unoccupied molecular orbital of AN being larger than the value of highest occupied molecular orbital of [Fe–MCA@SS/PMS]*. This study sheds new light on the preparation of BC-based SACs catalyst with efficient nonradical oxidation ability and an excellent feasibility to remove electron-rich organic pollutants in groundwater.