Discerning the Relevance of Superoxide in PFOA Degradation

Abstract

Perfluorooctanoic acid (PFOA) is a widely distributed recalcitrant contaminant. In recent years, advanced oxidation processes have been explored for PFOA degradation, yet factors influencing their efficacy and degradation mechanism are not fully understood. Here, we resolve ambiguity in the literature regarding the role of superoxide in PFOA degradation (e.g., by nucleophilic attack) by considering three pure superoxideproducing systems: KO 2 in dimethyl sulfoxide, xanthine oxidase with hypoxanthine, and WO x /ZrO 2 catalyst with H 2 O 2 . Superoxide production was confirmed in all systems by electron paramagnetic resonance spectroscopy and by precipitation of nitroblue tetrazolium, a common superoxide probe. Positive control experiments showed that the produced superoxide degrades ∼48% of bisphenol A within 1 day, corroborating the fact that superoxide was sufficiently stable and available for reaction in the test systems. However, no PFOA degradation was observed, which was corroborated by the absence of fluoride and degradation byproducts in all three systems. Therefore, other reaction pathways should be explored for PFOA degradation.

Site-Selective Loading of Single-Atom Pt on TiO2 for Photocatalytic Oxidation and Reductive Hydrodefluorination

“…61,62 Superoxide, which is abundantly obtained from reductive photocatalysis, is also known to be relatively ineffective for the degradation of perfluorooctanoic acid (PFOA). 63 While the cleavage of the C−F bond in PFOA using photogenerated holes has been demonstrated using boron- 64 and bismuth-based photocatalytic materials, 65 it requires very high valence hole potentials above 4 eV (vs NHE).…”

“…Recently, defluorination of poly- and perfluoroalkyl substances (PFASs) was explored to more efficiently utilize the conduction band electrons produced by the photocatalyst and to more thoroughly investigate the unique properties that emerge with downsizing the Pt cocatalyst to the atomic scale. PFAS have garnered significant attention in recent years, due to elevated concerns regarding their potential human health risks and persistence in the environment due to the high C–F bonding and dissociation energy (∼450 kJ mol –1 ). , Conventional AOPs are often ineffective in the treatment of PFAS, as these compounds have negligible reactivity toward •OH. , Superoxide, which is abundantly obtained from reductive photocatalysis, is also known to be relatively ineffective for the degradation of perfluorooctanoic acid (PFOA) . While the cleavage of the C–F bond in PFOA using photogenerated holes has been demonstrated using boron- and bismuth-based photocatalytic materials, it requires very high valence hole potentials above 4 eV (vs NHE).…”

Thermal Regeneration of Spent Granular Activated Carbon Presents an Opportunity to Break the Forever PFAS Cycle

“…Ubiquitous presence of recalcitrant per- and poly fluoroalkyl substances (PFAS) in the natural and engineered aqueous environment is well documented. , These forever chemicals undergo long-range transport through air and water. , In addition, these are challenging to destroy due to the strength (544 kJ/mol) and the shielding effect of polar covalent C–F bonds from negatively charged reactive oxygen species. − PFAS are also highly resistant to biodegradation due to microbial inaccessibility of the carbons and these molecules being poor electron donors , although recent studies showed that biodegradation can potentially be achieved with pure cultures of microorganisms in well-controlled laboratory settings over weeks/months. − As a result, nondestructive remediation and treatment strategies are deemed pragmatic and necessary to remove PFAS from water. Granular activated carbons (GAC)/ion exchange resins in the engineered water treatment and remediation systems, geoliners in landfills, as well as containment barriers in emission control in the incinerators are interventions and can contain and remove PFAS from the natural environment. − The containment or adsorption of PFAS (e.g., by GAC) are imperative measures; however, inadequate disposal, transportation, and storage of the PFAS-laden adsorbents can introduce PFAS back into the environment .…”

A Cruciform Petal-like (ZIF-8) with Bactericidal Activity against Foodborne Gram-Positive Bacteria for Antibacterial Food Packaging

“…The presence of superoxide anions(•O 2 − ) can be detected using nitrotetrazolium blue chloride (NBT). The •O 2 − anions can combine with NBT in DMSO solution to produce a blue-violet compound that can be detected at 529nm [ 38 ]. We discovered the presence of •O 2 − in solutions of both forms of ZIF-8 when they are illuminated ( Figure 3 C,D).…”