Iron-based nitrogen-rich metal-organic framework structure for activation of hydrogen peroxide and peroxymonosulfate for ultra-efficient tetracycline degradation

Fe-based metal-organic frameworks (Fe-MOFs) have been used to catalyze the degradation of organic pollutants; however, the underlying mechanism remains unclear. In this study, we prepared Fe-MOF catalysts featuring a three-dimensional ordered structure and active Fe-N4 coordination centers using self-designed polypyrazole compounds as ligands. Because the coordination centers are similar to the classical single-atom Fe-N4 active neutral structure, Fe-MOFs exhibit excellent performance in activating hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) for the degradation of antibiotics. Moreover, the two adjacent nitrogen atoms in pyrazole strengthen the interaction with active neutral Fe, thereby enhancing the efficiency and selectivity of the catalytic sites. In the presence Fe-MOF/H2O2, a free radical process involving hydroxyl radicals (center dot OH) is activated to achieve a degradation rate of 98.36 % for tetracycline (TC) within 10 min. In a Fe-MOF/PMS system, 97.01 % of TC can be degraded within 10 min through a non-free radical process with singlet oxygen (1O2) as the primary active species. The high degradation efficiency of Fe-MOF is primarily attributed to its highly catalytically active structure, which exerts a van der Waals force effect on the pollutants, thereby facilitating electron transfer between the pollutants and active centers. This shortens the distance between the pollutants and Fe catalytic center, enhances electron transfer, and promotes the chemical adsorption of H2O2 and PMS to form FeN4-H2O2 and FeN4-PMS, respectively. Additionally, the strong coordination within the Fe-N4 pyrazole structure significantly suppresses Fe leaching, facilitating a stable adsorption configuration.