Low-temperature mineralization of perfluorocarboxylic acids

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative pollutants found in water resources at concentrations harmful to human health. Whereas current PFAS destruction strategies use nonselective destruction mechanisms, we found that perfluoroalkyl carboxylic acids (PFCAs) could be mineralized through a sodium hydroxide–mediated defluorination pathway. PFCA decarboxylation in polar aprotic solvents produced reactive perfluoroalkyl ion intermediates that degraded to fluoride ions (78 to ~100%) within 24 hours. The carbon-containing intermediates and products were inconsistent with oft-proposed one-carbon-chain shortening mechanisms, and we instead computationally identified pathways consistent with many experiments. Degradation was also observed for branched perfluoroalkyl ether carboxylic acids and might be extended to degrade other PFAS classes as methods to activate their polar headgroups are identified.

Solvent-Free, Ambient Temperature and Pressure Destruction of Perfluorosulfonic Acids under Mechanochemical Conditions: Degradation Intermediates and Fluorine Fate

“…While the initial concentrations for each PFSA were different, the observed trend may be attributed to the increasing average BDE of the C–F bond as the chain length decreases (Table S5). Thus, degradation rates can be expressed as PFOS (C8) > PFHpS (C7) > PFHxS (C6) > PFPeS (C5) > PFBS (C4), in line with previous studies. , The difference in BDEs among other PFASs is an underlying cause of differing degradation rates between subgroups subjected to MCD treatment. For example, PFCAs degrade faster than PFSAs due to lower BDEs of the more reactive α-C–F adjacent to the functional group head. , Tracking target PFSA degradation revealed interesting but, arguably, expected outcomes based on the results of previous PFAS studies that employed MCD.…”

“…16 Thus, degradation rates can be expressed as PFOS (C8) > PFHpS (C7) > PFHxS (C6) > PFPeS (C5) > PFBS (C4), in line with previous studies. 16,24 The difference in BDEs among other PFASs is an underlying cause of differing degradation rates between subgroups subjected to MCD treatment. For example, PFCAs degrade faster than PFSAs due to lower BDEs of the more reactive α-C−F adjacent to the functional group head.…”

“…The carbon–fluorine (C–F) bond is one of the strongest single bonds known with bond dissociation energies (BDEs) up to 130 kcal mol –1 . , As a result, PFASs are significantly more resistant to environmental and targeted degradation than nonfluorinated POPs, while also being linked to various negative health effects. − Bioremediation is effective for chlorinated POPs but affects only partial degradation for PFASs in laboratory-scale experiments, with short-chain daughter products observed in the reaction mixture. , Recently, solution-based degradation techniques have also been proposed, but the extraction and concentration of PFASs, as well as the harsh conditions or lengthy reaction times required for complete degradation, mean that these methods are unlikely to be viable at scale, particularly for recalcitrant perfluorosulfonic acids (PFSAs). − Even incineration, which is generally used to destroy the most stable organic pollutants, does not culminate in the complete destruction of PFASs . Instead, incinerating PFAS-impacted wastes or PFAS-containing products emits greenhouse gases, compounds of partial combustion, and residual PFASs in the ash …”

Efficient Recognition and Removal of Persistent Organic Pollutants by a Bifunctional Molecular Material

“…Herein, we report that rapid detection and effective removal of PFOS can be achieved by a bifunctional molecular nanocage (1). 1 shows an unusual turn-on fluorescence response to PFOS and a strong binding constant of 5.21 × 10 6 M −1 , which is 2 orders of magnitude higher than the previous record delivered by the inclusion complex of β-CD and linear perfluorochemicals.…”

Atomistic insights into the hydrodefluorination of PFAS using silylium catalysts

“…Despite this challenge, a wide range of techniques has been introduced in the literature, including chemical reduction using solvated electrons, 55,57 electrochemical reduction, [58][59][60] degradation via application of plasma, [61][62][63] photochemical reduction, 64,65 thermal degradation, 66 oxidation via activated persulfate, 67,68 microbial degradation, 69 and chemically assisted degradations, [70][71][72][73] through the application of sound waves, 74 and through low-temperature hydroxide-mediated decarboxylation and deuorination. 75 In regards to the question of in situ versus ex situ degradation, it should be mentioned that degradation can produce a variety of chemical byproducts that can result in adverse reactions in the environment. 76,77 What is clear from the existing literature is that there is a clear need to understand the chemical nature of the C-F bond, and how to best design chemical processes for degrading/transforming it.…”