Green preparation of pyrrhotite-activated H2O2 for tetracycline degradation: performance and mechanism

Pyrrhotite (Fe_1-xS) was prepared by the pyrolysis of pyrite and the sulfidation of hematite, and subsequently used to activate H₂O₂ for the degradation of tetracycline (TC). The pyrite-derived Fe_1-xS samples (P600 and P700) and the hematite-derived Fe_1-xS samples (S600, S700), prepared at 600 and 700 °C, respectively, were characterized using X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XRS), scanning electron microscopy (SEM) and magnetism analysis. The effects of annealing temperature, preparation method, and initial solution pH on TC degradation were systematically investigated. The results showed that the degradation of TC increased with the decrease in annealing temperature and initial solution pH. Quenching experiments and electron spin resonance (ESR) demonstrated that ^•OH and ¹O₂ were reactive oxygen species (ROSs) in acidic and alkaline media, respectively. Moreover, the sulfidation-derived pyrrhotite, featuring a monoclinic Fe_1-xS shell, exhibited superior catalytic performance than pyrolysis-derived pyrrhotite with a hexagonal Fe_1-xS shell. Notably, ¹O₂ was easier to produce in the P600/H₂O₂ system. Both P600 and S600 maintained a high catalytic activity after five runs. These findings offer a novel approach for pyrrhotite preparation and promote the comprehensive utilization of pyrite and hematite.