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

Pyrrhotite (Fe1-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 Fe1-xS samples (P600 and P700) and the hematite-derived Fe1-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 Fe1-xS shell, exhibited superior catalytic performance than pyrolysis-derived pyrrhotite with a hexagonal Fe1-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.