Synergetic decomposition performance and mechanism of perfluorooctanoic acid in dielectric barrier discharge plasma system with Fe3O4@SiO2-BiOBr magnetic photocatalyst

Abstract

The Fe3O4@SiO2-BiOBr (FSB) magnetic composite was prepared and introduced into the dielectric barrier discharge (DBD) system as a heterogeneous Fenton-like photocatalyst for synergistic degradation of perfluorooctanoic acid (PFOA). The FSB was characterized by X-ray diffraction, UV–vis diffuse reflectance spectra, energy dispersive X-ray spectroscopy and scanning electron microscope. Characterization results demonstrated that BiOBr was successfully coated on Fe3O4@SiO2, forming FSB, and it exhibited good UV & visible response. The presence of FSB accelerated PFOA degradation: PFOA removal efficiency and total organic carbon removal from DBD-FSB system increased from 73.5% to 92.9% and 28.9% to 62.5%, respectively, within 60min under reaction conditions of 20mgL−1 PFOA, initial pH 4.28, 100mgL−1 FSB and 22kV peak voltage, as compared with DBD system. Accordingly, defluorination efficiency of PFOA and energy efficiency increased from 21% to 32.8% and 46.39mgkW−1h−1 to 72.47mgkW−1h−1, respectively. The synergetic mechanism was attributed to the combination of active species such as OH, H2O2, O3, directly generated from the DBD plasma and a great amount of OH generated from Fenton-like reaction initiated by FSB photocatalyst under light irradiation emitted during discharge. The OH and photogenerated holes played essential roles in the mineralization process. Based on the identified intermediates, possible degradation pathways of PFOA in DBD-FSB system were proposed, and PFOA degradation mainly occurred via the pathway of perfluoroalkyl radical pathway.