Fe-Phenanthroline derived FeNx coordinated chitosan effectively activates peroxymonosulfate to degrade tetracycline through both radical and non-radical pathways

Abstract

Fe-Nx sites can activate peroxymonosulfate (PMS) in advanced oxidation processes (AOPs) to produce various reactive oxygen species, and have great potential for removing tetracycline (TC), but their formation and catalytic mechanism are rarely studied. Herein, the Fe/N-C catalyst was prepared by crosslinking chitosan (CS) using a coordination complex of Fe2+ and phenanthroline as the precursor for FeNx. The results of crystal structure, lattice constant, chemical state of N element and structural analysis have demonstrated the successful construction of FeNx sites. The degradation experiments confirmed that the removal efficiency of tetracycline reached up to 90.7 % within 15 min, with a degradation rate of up to 0.184 min−1. Moreover, the material has exhibited excellent performance in complex water environments and within a broad pH range (pH = 2.30 ∼ 9.88). Mechanism analysis proves that the active substances in the system are 1O2, •O2−, SO4•−, •OH and FeIV = O, of which 1O2 played the principal role. The FeNx structure is the primary active site, where the redox cycle between Fe2+ and Fe3+, electron transport between pyridinic N, electron-deficient C and PMS produces active components. In addition, based on the various intermediate products detected, two possible TC degradation pathways are reasonably speculated. In this study, the highly active FeNx sites were successfully constructed, and elucidated their activation mechanism towards PMS, which proved the broad prospect of Fe/N-C materials in pollutant degradation.