Visible light-Fenton degradation of tetracycline hydrochloride over oxygen-vacancy-rich LaFeO3/polystyrene: Mechanism and degradation pathways

In this study, the oxygen–vacancy–rich (OV) lanthanum ferrite (LaFeO3) perovskite (also called LFO) was successfully prepared by an ultrasound–assisted sol–gel method and hydrothermally loaded onto polystyrene (PS) to obtain LaFeO3/polystyrene–oxygen–vacancies (LFO/PS–OVs). The structure and properties of LFO/PS–OVs were investigated using scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X–ray photo–electron spectroscopy (XPS), photoluminescence spectra (PL) and other characterization methods. The authors also investigated the effects of hydrogen peroxide (H2O2) concentration, catalyst dosage, solution concentration, pH and inorganic anions on the tetracycline hydrochloride (TC) removal efficiency. According to the results, the ultrasonic cavitation treatment and the composite reaction significantly increased the specific surface area of LFO as well as the content of oxygen vacancies and broadened the forbidden band width of LFO. The significant improvement in catalytic activity can be attributed to solving the agglomeration problem of powdered LFO and the introduction of a large amount of OVs. The degradation mechanism was proposed according to the free radical capture experiments and the electron spin resonance (ESR) tests. Based on the DFT calculations and identification of intermediates by LC/MS, the main degradation pathways of TC were proposed. The results showed that reactive oxygen species (ROS) may preferentially attack atoms with the high f0 values of Fukui index. This study gives an insight into the promising application of oxygen–vacancy–rich perovskite/polystyrene composites in environmental remediation.