Degradation and Defluorination of Per- and Polyfluoroalkyl Substances by Direct Photolysis at 222 nm

Abstract

The susceptibility of 19 representative per- and polyfluoroalkyl substances (PFAS) to direct photolysis and defluorination under far-UVC 222 nm irradiation was investigated. Enhanced photolysis occurred for perfluorocarboxylic acids (PFCAs), fluorotelomer unsaturated carboxylic acids (FTUCAs), and GenX, compared to that at conventional 254 nm irradiation on a similar fluence basis, while other PFAS showed minimal decay. For degradable PFAS, up to 81% of parent compound decay (photolysis rate constant (k 222 nm) = 8.19–34.76 L·Einstein–1; quantum yield (Φ222 nm) = 0.031–0.158) and up to 31% of defluorination were achieved within 4 h, and the major transformation products were shorter-chain PFCAs. Solution pH, dissolved oxygen, carbonate, phosphate, chloride, and humic acids had mild impacts, while nitrate significantly affected PFAS photolysis/defluorination at 222 nm. Decarboxylation is a crucial step of photolytic decay. The slower degradation of short-chain PFCAs than long-chain ones is related to molar absorptivity and may also be influenced by chain-length dependent structural factors, such as differences in pK a, conformation, and perfluoroalkyl radical stability. Meanwhile, theoretical calculations indicated that the widely proposed HF elimination from the alcohol intermediate (C n F2n+1OH) of PFCA is an unlikely degradation pathway due to high activation barriers. These new findings are useful for further development of far-UVC technology for PFAS in water treatment.

Organic Contaminants and Potable Reuse: Perspectivesto 2050

“…Krypton chloride excimer lamps emit at 222 nm and have demonstrated higher concentrations of oxidizing radicals compared with low-pressure mercury lamps, potentially reducing UV dose requirements. Photons at 222 nm can destroy PFAS by direct interaction with light that are recalcitrant to 254 nm light (Xin et al 2023).…”

Investigation on UV Degradation and Mechanism of 6:2 Fluorotelomer Sulfonamide Alkyl Betaine, Based on Model Compound Perfluorooctanoic Acid

“…PFASs are extensively used in a wide range of industrial and commercial applications including paints, cookware, water-repellent textiles, alkaline cleaners, packaged foods, carpets, upholstery, shampoos, and firefighting foams [4,5]. From PFAS-containing products, these substances are discharged into industrial and municipal wastewater, leading to their ubiquitous occurrence in different environmental compartments including wildlife tissues, human blood, and breast milk [6].…”

“…Many of these substances contain perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) as backbone structures [7]. They have non-enforceable lifetime health advisory levels set at 2 of 16 70 parts per trillion (ppt) by the U.S. Environmental Protection Agency (US EPA) in 2016 [6]. PFOA has been associated with adverse health effects, including potential links to cancer, reproductive issues, and impacts on the liver, while also posing environmental concerns due to its bioaccumulation and long-lasting presence in ecosystems [8].…”

Far UV light in water treatment via producing reactive oxidative species

“…Compared with UV254 irradiation, UV222 irradiation shows higher inactivation efficiency against UV-resistant virus such as adenovirus and bacteriophage Phi6 14,15 as well as bacteria such as E. coli 15 . It is also gaining attention for the direct decomposition of emerging contaminants, such as carbamazepine, N-nitrosodimethylamine and PFASs [16][17][18] . Furthermore, it can efficiently activate H2O2, chlorine and peroxydisulfate (PDS) to generate ROS for the promotion of contaminants degradation 16,19,20 .…”