Ultraviolet-activated persulfate (UV/PS) represents a promising advanced oxidation process (AOP) for the elimination of toxic and bio-refractory organic pollutants in wastewater due to the advantages of SO 4 • - . C7 HFPO-TA, one of the latest alternatives to PFOA in fluoropolymers production, with a unique structural fragment (CF 3 O-CF(CF 3 )-) that has been frequently identified in effluents, surface waters, and sediments in proximity to fluorochemical industrial zone. In this study, we evaluated the degradation of C7 HFPO-TA and co-existing PFHxA in AOPs, mainly focusing on the molecular structure effect on the chemical affinity with different reactive species (RSs). The results showed that >99.9% C7 HFPO-TA and PFHxA could be decomposed after 480 min in UV/PS, significantly outperforming UV/H 2 O 2 (<10%), as the result of the synergistic effect of radical/non-radical (SO 4 • - /HSO 4 •, O 2 • - , HO•, 1 O 2 ) and chain reactions. The degradation mechanism of C7 HFPO-TA was primarily governed by the DHEH mechanism, which facilitated radical chain reactions and resulted in the formation of a new perfluoroalkyl ester intermediate (C 6 F 12 O 3 ), as optimized by Transition State theory. The degradation of five HFPO and three PFCA was highly dependent on their molecular structures. Degradation kinetics and DFT calculations demonstrated the longer branched fluorocarbon chain could diminish the steric hindrance of α-CF 3 in HFPO and made the electron distribution more flexible for the reaction with the RSs. The comprehensive analysis of degradation kinetics, theoretical calculations and intermediates analysis elucidated the transformation mechanisms of C7 HFPO-TA and PFHxA in UV/PS.
Short-chain perfluoroalkyl carboxylic acid (PFCAs) have been widely detected in aquatic systems, posing adverse threats to human health and the environment. However, the effective remediation of short-chain PFCAs in contaminated groundwater remains a major challenge. In this study, Zr-based metal-organic framework UiO-67—featuring tetrahedral cages (12 Å) and octahedral cages (14 Å)—was employed as a platform for precise pore microenvironment regulation. A new modulation strategy using glycine hydrochloride enabled the introduction of linker defects, thereby enhancing the surface positive charge and electrostatic interactions. By incorporating amine and fluorophilic CF 3 functional groups into the organic ligands, three UiO-67 series MOFs, UiO-67-X (X = H, NH 2 , 2CF 3 ), were synthesized for efficient removal of perfluorohexanoic acid (PFHxA) from aqueous solution. Among them, UiO-67–2CF 3 , with a hierarchical pore structure (0.89 nm, 1.14 nm), exhibited exceptional PFHxA adsorption capacity (1386 mg/g), rapid adsorption kinetics (4 min), and excellent selectivity and recyclability. Continuous column breakthrough experiments further demonstrated that UiO-67–2CF 3 effectively reduced PFHxA concentrations from 1 μg/L to below 10 ng/L. In addition, experimental characterizations and DFT theoretical calculations revealed that the adsorption mechanism involves electrostatic interaction, F···F interactions, Lewis acid-base interactions, anion–π interactions, CF 3 –π interactions and hydrogen bonding. These excellent adsorption performances highlight UiO-67–2CF 3 as a promising material for the remediation of short-chain PFCA-contaminated water. This study also provides new insights into the rational design of advanced adsorbents for short-chain PFCAs removal.
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