Trace Co coupled and tourmaline doped g-C3N4 for visible-light synergistic persulfate system for degradation of perfluorooctanoic acid

Abstract

Removal of perfluorinated compounds (PFCs) from the environment is a major challenge due to their refractory, persistent and bioaccumulative properties. In this study, trace Co coupled via Co–P coordination and tourmaline (TM) doped g-C3N4 was fabricated (marked as Co/TM/g-C3N4) and used as the catalyst for activating peroxymonosulfate (PMS) to remove emerging PFOA under visible light irradiation. Several affecting parameters were systematically investigated, inlcuding Co/TM/g-C3N4 dosage, PMS concentration, initial pH, as well as coexisting Cl−, HCO3−, H2PO4−, NO3− and humic acid. Under the conditions of 0.5 g/L Co/TM/g-C3N4, 2.5 g/L PMS and pH 3.0, the developed synergistic system had the ability for 81.11% removal of PFOA within 4 h, 67.64% removal after the fourth run, and also could be effectively applied in actual water bodies. During the degradation process, π-π*, N–CN and graphite N played the vital role, with the final defluorination rate of 31.12% at 4 h. Free radical quenching and quantitative analysis, as well as electron paramagnetic resonance was used to verify the free radical and non-free radical pathways for PFOA removal, with the findings that SO4•− (2.61 μM at 1 h), •OH (0.067 μM at 4 h), O2•−, h+, and O12 were involved with possible time-dependent. By liquid chromatography-mass spectrometry analysis, the short-chain intermediates of C3–C7 were proposed and identified. From this study, trace Co coupled and TM doped g-C3N4 demonstrated higher catalytic potential to activate PMS for visible-light synergistic PFOA removal, with the expectation of achieving a cleaner water environment for human beings.