Efficient degradation and defluorination of perfluorobutyric acid under UV irradiation in the presence of persulfate

Perfluorobutyric acid (PFBA) has been used more and more in recent years and also can be generated by the degradation of long-chain perfluorinated compounds (PFCs). PFBA is refractory and has various toxic effects on the human body, such as reproductive toxicity and hepatotoxicity. Therefore, the removal of PFBA from the environment effectively has become a very urgent issue. This study successfully applied an ultraviolet-activated persulfate (UV/PS) system to remove PFBA (50 μM, 120 mL). We found that a high decomposition ratio (88.0%) and defluorination ratio (39.6%) can be achieved under an initial pH of 2.00 ± 0.02 within 5 h at room temperature. Quenching test and electron paramagnetic resonance spectrum of active species were conducted to develop the proposed mechanism for PFBA oxidation, and they depicted PFBA lost CF2 unit step by step to form short-chain intermediates (PFPrA and TFA) and F−, which became H2O and CO2 eventually. Sulfate radical (SO4•-) and hydroxyl radical (•OH) play key roles in the degradation of PFBA. The lower initial pH under acidic conditions and the higher pH under alkaline conditions can accelerate the degradation of PFBA by affecting the active species in the system. Higher persulfate doses or greater light intensity resulted in a faster PFBA degradation. Meanwhile, the inhibitory effect of Cl− on the decay of PFBA was significant, while other coexisting anions (CO32−, SO42−, F−) and humic acid had a slight influence. To the best of our knowledge, this is the first report for systematic studying the efficient degradation and defluorination of PFBA. This paper will guide the follow-up research on the degradation of short-chain perfluorinated compounds.