Efficient Reductive Decomposition of Perfluorooctanesulfonate in a High Photon Flux UV/Sulfite System

Abstract

Hydrated electron (e) induced reduction techniques are promising for decomposing recalcitrant organic pollutants. However, its vigorous reactivity with copresent scavenging species and the difficulty in minimizing the competitive reactions make the proportion of e participating in pollutant decomposition low, reflecting by slow decomposition kinetics. In this study, a high photon flux UV/sulfite system was employed to promote e production. Its feasibility in enhancing a notorious recalcitrant pollutant, PFOS, decomposition was investigated. The effective photon flux utilized for producing e was 9.93 × 10 einstein/cm·s. At initial solution pH 9.2, with DO about 5 mg/L, and at around 25 °C, 98% PFOS was decomposed within 30 min from its initial concentration of 32 μM. The k of PFOS decomposition was 0.118 min (7.08 h), and about 8-400 folds faster than those obtained in other reductive approaches. In this system, PFOS decomposition showed can tolerate copresent 7 mg N/L of NO. Suggested by molecular orbitals and thermodynamic analyses, the mechanisms responsible for PFOS decomposition involve defluorination, desulfonation, and centermost C-C bond scission. By demonstrating a more practical relevant treatment process, the outcomes of this study would be helpful for facilitating future applications of e induced reduction techniques for efficient recalcitrant pollutants decomposition.

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

“…They also showed that NO 3 − has a negative influence on the degradation of PFOA. Gu et al used a similar system and degraded 98% of PFOS at 25 °C and a pH of 9.2 with a defluorination rate of approximately 50% after 30 min [ 88 ]. Bentel and co-workers operated the UV/sulphite system with a higher pH of 12 [ 75 ].…”

Fast Degradation of Monochloroacetic Acid by BiOI-Enhanced UV/S(IV) Process: Efficiency and Mechanism

“…Recently, efficient degradation of some halogenated organic compounds (HOCs) and hazardous oxoanions was achieved through UV-activated (bi)sulfite (S(IV)) reduction (abbreviated as UV/S(IV)) [1][2][3], which is classified as a hydrated electron (e − aq )-based advanced reduction process (e − aq -ARP). However, besides the valid concentration of S(IV) (main precursor of e − aq ), UV photon absorbance by S(IV) dominates the production efficiency of e − aq for this reduction process [4].…”

Directional electron transfer mechanisms with graphene quantum dots as the electron donor for photodecomposition of perfluorooctane sulfonate

“…What's more, a short electron pathway between the GQDs interior and the surface due to the quantum size can enhance the electron transfer as well [39]. GQDs acted as the electron 15 donors in this process, in which electrons can be easily transferred to the surface of SiC nanoparticles. And then PFOS, which accumulated on the surface of SiC due to the surface-active properties, would act as the final electron acceptor for the electron-withdrawing property of sulfonate group.…”

“…, the branched PFOS decomposed much faster than the linear isomers [15,22]. It was because that photon and e aq directly reacted with PFOS molecule in solution, and the C-F bond in branched isomers was more vulnerable to reductive decomposition than the linear isomers for the higher electron affinity [41].…”

“…According to the previous researches, PFOS decomposition started with the cleavage of -F 2 C-SO 3 H bond, thus the focus of PFOS decomposition was how to realize initial activation of sulfonate group [13,14]. Sulfonate group in PFOS is 4 recalcitrant to traditional advanced oxidation processes (AOPs), while the hydrated electron (e aq -) induced reduction has been recently demonstrated to be effective to activate the sulfonate group [15,16]. However, due to the high reactivity of e aq with other coexistent oxidative species in solution, a large amount of chemical agent (molar concentration, I -: PFOS = 500 : 1) that can promote the e aq production was necessary to ensure fast decomposition kinetics [16].…”