Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management

Unveiling the directional dynamics: Hydrated electron driven defluorination in PFOA⁻ and PFOS⁻ through ab Initio molecular dynamics and quantum chemistry

Hydrated electrons (e-(aq)) are recognized for their potent reducing capabilities, making them significant in environmental engineering, particularly in the degradation of persistent pollutants like perfluoroalkyl compounds (PFCs). This study investigates the influence of attack direction of e-(aq) on the degradation mechanisms of PFCs, addressing a critical gap in understanding due to experimental limitations. Utilizing ab initio molecular dynamics and quantum chemical calculations, we systematically simulated the attack direction of e-(aq) on PFCs, focusing on the formation of anionic radicals and their excited-state reactivity. Our results indicate that the attack direction is pivotal for C-F bond cleavage: e-(aq) targeting the carboxyl end promotes effective bond cleavage, while approaches from the carbon-fluorine chain are hindered by molecular orbital shielding effects. Furthermore, we demonstrate that employing micellar systems to maintain PFCs in an unsolvated anionic state significantly reduces excitation energy, enhances red-shifted absorption, and increases excitation probability. Importantly, the excited-state electronic structure of PFCs closely mirrors that of their anionic radicals. These findings provide a novel strategy for improving the degradation of PFCs, thereby advancing treatment processes for persistent environmental pollutants and contributing to the broader understanding of water quality management.

Theoretical and experimental insights into the degradation mechanism of PFBS under subcritical hydrothermal conditions

Per- and polyfluoroalkyl substances (PFAS) are known for their strong C-F bonds, which make them highly persistent in the environment and resistant to degradation. Among PFAS, perfluorobutane sulfonate (PFBS), a short-chain PFSA widely used as a replacement for long-chain PFAS like perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), has garnered attention due to its environmental persistence and toxicity. Although PFBS has lower bioaccumulation potential than its long-chain counterparts, it remains a significant pollutant with limited data available on its degradation mechanisms. To address this, the present study investigates PFBS degradation under subcritical water hydrothermal conditions. Various alkaline substances and additives were tested, and degradation products were analyzed by liquid and gas chromatography-mass spectrometry. Results show that 2 M NaOH at 325°C achieved an ∼99.4 % PFBS removal rate, and the degradation pathway began with the breakdown of the S-C bond, followed by C-F bond cleavage, resulting in the formation of smaller fluorinated compounds, including trifluoroacetic acid. Density functional theory (DFT) calculations provided detailed insights into the degradation mechanism, identifying hydroxide ion attack on the sulfonic acid group as the initial step and elucidating three distinct pathways for subsequent reactions. This study provides key insights into PFBS degradation mechanisms, emphasizing the synergistic effect of alkaline bases and additives. The findings support the optimization of subcritical hydrothermal treatment for PFAS removal, providing a scalable and environmentally sustainable solution.

Sustained hydrated electron production for enhanced reductive defluorination of PFAS in groundwater

Hydrated electrons (eaq‒; ‒2.9 V) are effective at defluorinating per- and polyfluoroalkyl substances (PFAS), but production of eaq‒ often requires excess source chemicals, anoxic environment, and harsh pH conditions. To improve the feasibility of the reductive process, we harnessed phenol as a source chemical yielding four eaq‒ stoichiometrically and utilized dithionite (DTN) to catalyze phenol cycle for sustained eaq‒ yields. The added DTN not only scavenges dissolved oxygen, the eaq‒ trap, but also reductively transforms phenol degradation product, p-benzoquinone, to hydroquinone which yields more eaq‒ upon UV irradiation. In the UV/phenol/DTN system, up to 70 % defluorination of PFOA solution was achieved while the impact of groundwater matrix was minor on the degradation performance of PFOA, PFOS and GenX. Especially in acidic conditions, •H, the conjugate acid of eaq‒, is the dominant radical for decomposing the three tested PFAS. Density functional theory calculations reveal hydrogen bonding and van der Waals interactions between PFAS and phenol, facilitating both decarboxylation and fluorine elimination in PFAS structures. The combined experimental and theoretical evidence demonstrated the capability of the new UV/phenol/DTN method to sustain eaq‒ production for effective defluorination of PFAS in the groundwater matrix.

Advancements in artificial intelligence-based technologies for PFAS detection, monitoring, and management

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants with strong carbon‑fluorine (CF) bonds that contribute to bioaccumulation and long-term environmental and health risks. Traditional PFAS detection and treatment methods are often time-consuming, costly, and limited in scope. Recently, artificial intelligence (AI)-based technologies, particularly machine learning (ML), have emerged as powerful tools for enhancing PFAS monitoring, source identification, and remediation. ML models such as random forest (RF), gradient boosting decision trees (GBDT), support vector machines (SVM), and artificial neural networks (ANN) have been successfully applied to classify PFAS contamination sources with over 96 % accuracy, predict PFAS concentrations in groundwater with an AUC of 0.90, and optimize removal processes such as nanofiltration and adsorption with R2 values exceeding 0.93. Despite these advancement, challenges remain in ensuring high-quality datasets, addressing data imbalance and improving model interpretability. Future research should focus on expanding public datasets, leveraging Automated ML (AutoML) for optimization, and integrating Al-driven sensors for real-time detection. AI-based approaches present a transformative opportunity to enhance efficiency, accuracy, and cost-effectiveness in PFAS management, aiding regulatory decision-making and environmental protection.

Deep Insight of the Mechanism for Nitrate-Promoted PFASs Defluorination in UV/Sulfite ARP: Activation of the Decarboxylation-Hydroxylation-Elimination-Hydrolysis Degradation Pathway

The UV/sulfite advanced reduction process (ARP) holds promise for the removal of per- and polyfluoroalkyl substances (PFASs) by a hydrated electron (eaq-)-induced H/F exchange process under anoxic conditions. Traditionally, the presence of coexisting nitrate in water has always been regarded as a major inhibitory factor for PFASs defluorination. However, this study observed an unexpected promotive effect of nitrate on defluorination, challenging the previous phenomenon. Notably, the addition of 100 μM nitrate resulted in a remarkable 54% enhancement in PFOA defluorination. A novel mechanism was discovered that nitrate-derived reactive nitrogen species (RNS) activated the decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) process, an important degradation pathway for PFASs in UV/sulfite ARP. Induced by eaq-, the PFAS molecule first became a perfluorinated radical and then was transformed into unstable perfluorinated alcohol by reacting with water. Due to the high reactivity driven by unpaired electrons of RNS, water molecules were destabilized with the H-O bond stretched from 0.98 to 1.04 Å. This effectively enhanced the spontaneity of the reaction between perfluorinated radical and water molecules and consequently made the whole DHEH process more thermodynamic favorable (ΔG, -23.53 → -376.28 kJ/mol). Such a process breaks through the view that the nitrate directly reacts with eaq- to affect PFASs defluorination in ARP systems. This finding offers an innovative perspective for optimizing PFAS defluorination by strategically regulating nitrate levels in water bodies.

Computational Studies of Enzymes for C-F Bond Degradation and Functionalization

Organofluorine compounds have revolutionized chemical and pharmaceutical industries, serving as essential components in numerous applications and aspects of modern life. However, their bioaccumulation and resistance to degradation have resulted in environmental pollution, posing significant risks to human and animal health. The exceptionally strong C-F bond in these compounds makes their degradation challenging, with current methods often requiring extreme experimental conditions. Therefore, the development of eco-friendly approaches that operate under milder conditions is crucial, with enzyme-mediated C-F bond cleavage strategies emerging as a particularly promising solution. In this review, we present an overview of how computational approaches, including molecular docking, molecular dynamics simulations, quantum mechanics/molecular mechanics calculations, and bioinformatics, have been utilized to investigate the mechanisms underlying enzymatic C-F bond degradation and functionalization. This review highlights how these computational approaches provide critical insights into the atomic-level interactions and energetics underlying enzymatic processes, offering a foundation for the rational design and engineering of enzymes capable of addressing the challenges posed by fluorinated compounds. This review covers several types of enzymes including: fluoroacetate dehalogenases, cysteine dioxygenase, L-2-haloacid dehalogenase, cytochrome P450, fluorinase and tyrosine hydroxylase.

Degradation and defluorination of C6F13 PFASs with different functional groups by VUV/UV-based reduction and oxidation processes

Structural diversity can affect the degradability of per- and polyfluoroalkyl substances (PFASs) during water treatment. Here, three PFASs with different functional groups-C6F13-R, PFHpA, PFHxS, and 6:2 FTS-were degraded using vacuum ultraviolet (VUV/UV)-based treatments. While fully fluorinated PFASs-PFHpA and PFHxS-were degraded faster in the VUV/UV/sulfite reaction than in VUV/UV photolysis, VUV/UV photolysis was more effective for degrading 6:2 FTS by OH radicals produced through photolysis of water. PFCAs such as PFHxA, PFPeA, and PFBA were formed by VUV/UV photolysis of PFHpA and 6:2 FTS, but the PFCA formation was inhibited in the VUV/UV/sulfite reaction. The degradation of the three PFASs in the VUV/UV/sulfite reaction was mainly carried out by H/F and SO3•-/F exchange mechanisms, mediated by hydrated electrons (eaq-) produced in the reaction. During the VUV/UV/sulfite reaction, PFCA precursors were first formed as transformation products, which were further transformed into PFCAs by the following VUV/UV/H2O2 reaction, implying enhanced defluorination of three PFASs. Our results indicate that VUV/UV-based treatments can be an option for PFAS degradation and defluorination by combining advanced reduction and oxidation processes and utilizing both eaq- and oxidative radicals.

Electrophotocatalysis for Reductive Defluorination of PTFE and PFASs

Polytetrafluoroethylene (PTFE) is among the most inert poly- and perfluoroalkyl substances (PFASs) and its degradation under mild conditions remains underdeveloped. We report a supercapacitor-assisted electrophotocatalysis, incorporating the strength of both electrochemical and photochemical energy, for the efficient defluorination of PTFE and other PFASs at low temperatures. CBZ6 worked as a photoreductant for injecting electrons into the inert carbon-fluorine bond, whereas the supercapacitor enabled the generation of the catalytically active species via an electrophotochemical process. Furthermore, the utilization of sunlight as the light source and supercapacitor as the electrical energy source makes the reaction portable and enables its outdoor applications.

PFAS removal via adsorption: A synergistic review on advances of experimental and computational approaches

Per- and polyfluoroalkyl substances (PFAS), commonly known as "forever chemicals", have become a major focus of current research due to their toxicity and persistence in the environment. These synthetic compounds are notoriously difficult to degrade, accumulating in water systems and posing long-term health and environmental risks. Adsorption is one of the most investigated technologies for PFAS removal. This review comprehensively reviewed the PFAS adsorption process, focusing not only on the adsorption itself, but also on the behavior of PFAS in the aquatic environment prior to adsorption because these behaviors directly affect PFAS adsorption. Significantly, this review summarized in detail the advances made in PFAS adsorption from the computational approach and emphasized the importance of integrated experimental and computational studies in gaining molecular-level understanding on the adsorption mechanisms of PFAS. Toward the end, the review identified several critical research gaps and suggested key interdisciplinary research needs for further advancing our understanding on PFAS adsorption.

Iron Doping of hBN Enhances the Photocatalytic Oxidative Defluorination of Perfluorooctanoic Acid

There is a growing need to effectively eliminate perfluorooctanoic acid (PFOA) from contaminated water, which requires extensive defluorination. Photocatalysis offers potential for PFOA degradation under ambient conditions without the need for treatment chemicals. However, photocatalytic treatment generally results in limited defluorination and, thus, incomplete elimination of potential toxicity and liability. This underscores the need to advance mechanistic understanding of the factors limiting PFOA oxidative defluorination. Here, we tested the hypothesis that direct electron transfer from PFOA to transition metals enhances photocatalytic defluorination. We developed a novel, facile approach to simultaneously functionalize and dope hexagonal boron nitride (hBN) (which is known to effectively catalyze photocatalytic PFOA oxidation) with Fe(III), using deep-eutectic solvents (DES). Addition of Fe(III) to synthesize Fe-hBN created new active sites for PFOA oxidation and doubled the defluorination extent (>40% fluoride release from initial 50 mg L-1 PFOA) compared to undoped hBN in 4 h reactions under 254 nm irradiation (64.4 W m-2). The mechanism of defluorination was elucidated through scavenger experiments that show the importance of photocatalytically generated electron holes for initiating PFOA degradation. Experiments also suggest that Fe(III) played a key role in PFOA removal, contributing to the improved extent of defluorination over undoped hBN. Density functional theory indicates that Fe(III) sites enable electrostatic adsorption of PFOA to the catalyst surface, enhance charge transfer, and promote hole localization to improve charge carrier separation, which is essential for oxidative defluorination of PFOA. This mechanistic insight informs catalytic material design to enhance oxidative defluorination processes.

Photodegradation of steroid hormone micropollutants with palladium-porphyrin coated porous PTFE of varied morphological and optical properties

In flow-through reactors, the photodegradation rate can be improved by enhancing contact and increasing the photocatalyst loading. Both can be attained with a higher surface-to-volume ratio. While previous studies focused on thin membranes (30 - 130 µm) with small pore sizes of 20 - 650 nm, this work employed poly(tetrafluoroethylene) (PTFE) supports, of which pore sizes are in the order of 10 µm, while the porosities and thicknesses are variable (22.5 - 45.3 % and 0.2 - 3 mm, respectively). These porous materials were anticipated to allow a higher loading of porphyrin photosensitisers and better light penetration for subsequent photodegradation of steroid hormone micropollutants via singlet oxygen (1O2) generation. The reactor surface refers to the surface within the PTFE pores, while the reactor volume is the total void space inside these pores. The surface-to-volume ratios between 105 and 106 m2/m3 are higher than those of typical microreactors (103 to 104 m2/m3). The weighted average light transmittance varied from 38 % with the thinnest and most porous support to 4.8 % with the thickest support. Good light penetration combined with minimal absorption by PTFE enhanced the light utilisation of the porphyrins when coated in the porous supports. Changes in the support porosity of the coated supports minimally affected steroid hormone removal, because the collision frequency in the very large pores remained relatively constant. However, varying the support thickness, porphyrin loading (0.3 - 7.7 μmol/g), and water flux (150 - 3000 L/m2.h), hence the resulting hydraulic residence time, influenced the collision frequency and steroid hormone removal. Results showed that the supports did not outperform membranes most likely because the larger pore size in the former limited contact between the hormones and 1O2. From photostability testing of the pristine supports, perfluoroalkyl substances (PFAS) released from the supports were found at 10 - 300 ng/L concentrations during accelerated ageing. While PFAS formation was detectable, the quantities during water treatment operations would be extremely low. In summary, this study elucidates the capability and limitations of porous supports coated with photosensitisers to remove waterborne micropollutants.

Accurate detection and high throughput profiling of unknown PFAS transformation products for elucidating degradation pathways

The accurate detection of unknown per- and polyfluoroalkyl substances (PFAS) transformation products (TPs) is essential for elucidating degradation pathways and advancing remediation strategies. Herein, we developed a workflow that combined Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with a paired mass distance (PMD) network. This study achieved high throughput profiling of PFAS TPs with mDa resolving power and sub-ppm mass error. UV treatment revealed chain-shortening pathways, while plasma treatment uncovered competing mechanisms of chain shortening and lengthening, generating oxygen-rich TPs with increased hydrophilicity. Specifically, UV treatment of a 15-PFAS mixture and contaminated natural water showed disappearance of 7 unknown PFAS homologues and the emergence of 12 unknown PFAS homologues. Despite PFAS persistence under UV exposure, previously undetected low-abundance PFAS species were identified, indicating non-negligible photochemical transformation. Under plasma treatment of isolated PFOS, 39 unknown PFAS homologues including 142 suspect and 34 unknown PFAS TPs were identified, highlighting the extensive transformation of emerging and persistent PFAS. Overall, our approach enabled accurate and high-throughput profiling of unknown PFAS TPs and their degradation pathways, providing new insights into persistent unknown PFAS.

Innovative hybrid approach for enhanced PFAS degradation and removal: Integrating membrane distillation, cathodic electro-Fenton, and anodic oxidation

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that pose significant toxicity risks to humans and ecosystems. Traditional advanced oxidation processes using boron-doped diamond (BDD) anodes degrade PFAS in wastewater effectively but suffer from slow kinetics and high energy costs, limiting commercial application. This study introduces a hybrid process combining cathodic electro-Fenton (EF), anodic oxidation via a BDD anode, and membrane distillation (MD) to improve perfluorooctanoate (PFOA) degradation efficiency and reduce energy use. Increasing the current density from 50 to 500 A/m2 significantly raised the concentration of produced H2O2 from 0.25 mM to 2.3 mM, accelerating PFOA degradation and mineralization. At 50 A/m2, no mineralization of PFOA occurred in the EF/BDD process, while the EF/BDD-MD process achieved 45% mineralization due to increased PFOA concentration in the electrolytic cell. At 500 A/m2, the EF/BDD-MD process achieved 95% PFOA mineralization. Findings reveal that while EF-generated •OH radicals assist degradation, the BDD(•OH) anode was the primary driver, driving 80% of the reaction. This degradation was initiated by direct electron transfer at the BDD surface, followed by homogeneous and heterogeneous •OH radicals enhancing the degradation and mineralization process. The hybrid process also lowered energy consumption, making the treatment feasible for large scales.

Metagenome-Assembled Genomes and Metatranscriptome Analysis of Perfluorooctane Sulfonate-Reducing Bacteria Enriched From Activated Sludge

Per- and polyfluoroalkyl substances (PFAS) exhibit a widespread distribution across diverse global ecosystems throughout their lifecycle, posing substantial risks to human health. The persistence of PFAS makes biodegradation a challenging yet environmentally friendly solution for their treatment. In the authors' previous study, a bacterial consortium capable of reducing perfluorooctane sulfonate (PFOS) was successfully enriched from activated sludge. This study aimed to investigate the array of genes associated with PFOS reduction via biosorption and biotransformation to elucidate the metabolic pathways. Two metagenome-assembled genomes (MAGs) based on 16S rRNA sequences that share 99.86% and 97.88% similarity with Hyphomicrobium denitrificans and Paracoccus yeei, respectively were obtained. They were found to contain several genes encoding enzymes that potentially regulate biofilm formation of biosorption and facilitate the desulfonation and defluorination processes of biotransformation. Transcriptomic analysis demonstrated the high expression levels of these genes, including alkanesulfonate monooxygenase, catechol dioxygenase, (S)-2-haloacid dehalogenase and putative cytochrome P450, suggesting their involvement in PFOS biotransformation. The expression of these genes supports the presence of candidate metabolites of PFOS biotransformation detected in the previous study. These findings emphasise the significant potential of bacterial consortia and the crucial role played by genes encoding enzymes in facilitating the remediation of PFOS contaminants.

New Insights into the Reductive Destruction of Per- and Polyfluoroalkyl Substances in Hydrated Electron-Based Systems

Per- and polyfluoroalkyl substances (PFAS) make up a class of highly toxic and persistent chemicals that have been widely detected in different environmental matrices. Recently, various hydrated electron-based techniques have been developed to destroy these compounds. However, the molecular mechanisms controlled by different hydrated electron photosensitizers are still unclear. Herein, we investigated the PFAS transformation processes in different hydrated electron-based systems, i.e., UV/Na2SO3, UV/indole, and UV/3-indoleacetic acid (IAA), using different perfluorocarboxylic acids (PFCA) as model compounds. By monitoring the production and decay of hydrated electrons, molecular interactions, and the generated intermediates, we systematically revealed the structure-property-performance mechanism of different systems. In the UV/Na2SO3 system, the disordered attack of hydrated electrons induced rapid destruction for either long or short-chain PFCA. However, the lower hydrated electron efficiency limited the final defluorination ratio. In the UV/indole system, the interaction between indole and PFCA promoted the directed transfer of hydrated electrons, resulting in a significantly higher destruction efficiency for long-chain PFCA than for short-chain PFCA. However, the self-quenching of hydrated electrons in the UV/IAA system led to the ineffective decomposition for all PFCA. This study provides mechanistic insights into the hydrated electron-induced PFAS decomposition processes, which would expand the designing strategies for improving PFAS destruction efficiency.

Synergetic degradation of PFOS by HALT conditions enhanced by Fe-based amorphous alloys

Global concern over per- and polyfluoroalkyl substances (PFASs), especially perfluorooctane sulfonate (PFOS), disposal prompts the search for effective degradation methods. Subcritical water hydrothermal treatment shows promise but suffers from unclear degradation pathways, hindering engineering application design due to unknown intermediate products. This study introduces Fe-based amorphous alloy to enhance the subcritical water hydrothermal degradation of PFOS, achieving a degradation rate of approximately 85 % under optimized conditions of 325 °C and 1 M sodium bicarbonate (NaHCO₃), compared to 56 % without the alloy. Analysis of liquid and gas-phase products, along with identification of potential intermediate products, led to proposing a reaction pathway for Fe-based amorphous alloy-enhanced subcritical water hydrothermal PFOS degradation. Additionally, the distribution of fluorine in PFOS was determined by fluorine-19 nuclear magnetic resonance (19F NMR), and the energy changes of key degradation steps were calculated based on DFT, which provided concrete evidence for the degradation process and verified the mechanism of subcritical hydrothermal degradation of PFOS enhanced by Fe-based amorphous alloys. Most importantly, the Fe-based amorphous alloy demonstrated effectiveness upon repeated use after water washing. These results endorse its potential as a PFOS degradation catalyst.

Cyclic removal and destruction of per- and polyfluoroalkyl substances from water using ion exchange, resin regeneration, and UV/sulfite reduction

Ion exchange (IX) can effectively remove per- and poly-fluoroalkyl substances (PFAS) from drinking water sources at ng/L to µg/L levels. However, adsorbed PFAS on spent resins should be further destructed for detoxification. Traditional resin incineration or landfilling may cause secondary pollution to the surrounding environment and cannot achieve resin reuse. This study explored three variations of a PFAS treatment train, aiming to completely defluorinate PFAS with different chain lengths and functional groups at environmentally relevant levels (ng/L) and to reuse the resins and solvents. The optimized treatment train includes IX, resin regeneration with 5 wt% NaCl and 60 % v/v methanol, distillation of waste regenerant, and advanced reduction by hydrated electrons (eaq-) generated during the ultraviolet/sulfite (UV/sulfite) treatment of still bottoms. Such a treatment train achieved nearly 100 % PFAS removal from surface water and groundwater using either PFAS-specific or generic resins, and almost 100 % defluorination of PFAS except a few short-chain fluorinated sulfonates and ethers. Regenerated resins had comparable PFAS removal to the pristine resins over three cycles. The generic resins (e.g., Dupont AmberLite™ IRA910) are easier to regenerate and thus are recommended for the treatment train over PFAS-selective resins (e.g., Purofine® PFA694E). Direct heterogenous defluorination on resins loaded with perfluorooctane sulfonate (PFOS) was ineffective, potentially due to the consumption of UV light/eaq- by the resins and insufficient contact between the UV light/eaq- with PFOS on the resin surface. Distillation of the waste regenerant successfully concentrated PFAS in the still bottoms, reduced the waste volume, and removed excess methanol, all essential for effective UV/sulfite treatment. Meanwhile, the produced condensate with high methanol contents and low PFAS levels can be reused for the next regeneration cycle. Findings from this study provide a timely and sustainable solution to the stringent and evolving regulations on PFAS and the resultant production of PFAS-laden resins as hazardous wastes.

Assessing the efficacy of the Plasma Spinning Disc Reactor (PSDR) in treating undiluted Aqueous Film Forming Foams (AFFFs)

This work used pulsed electrical discharge plasma to treat undiluted Aqueous Film Forming Foam (AFFF) solution that contained significant quantities of per- and polyfluoroalkyl substances (PFAS). The plasma was generated within a plasma spinning disc reactor (PSDR), which utilizes the electric breakdown of argon gas to create plasma over a thin liquid film generated on a spinning disc. The PSDR performance toward degradation of AFFF constituents such as fluorotelomers, perfluorinated C2-C7 alkyl acids, and unidentified precursors was investigated. The PSDR performance sensitivity to the process parameters, such as reactor electrode design, disc rotational speed, liquid flowrate across the disc, and discharge voltage, was explored. The results indicate degradation of all quantified PFAS with chain length ≥ 4 to below detection limit within a 250 mL sample after 86 h of treatment on a 6.5 cm disc rotating at 200 rpm. The overall PSDR performance was insensitive to the tested process parameters. A direct comparison with a UV/H2O2 process revealed the superior performance of the plasma-based treatment toward degradation of perfluorinated compounds, evidenced by higher precursor removal rates and lower energy consumption. The energy efficiency of the UV/H2O2 system was approximately 100 times lower than that of the plasma process under all conditions. This study confirms that PSDR is a promising technology for effectively remediating PFAS in undiluted AFFF.

Laccase based per- and polyfluoroalkyl substances degradation: Status and future perspectives

Per- and polyfluoroalkyl substances (PFAS) with stable carbon-fluorine bonds are used in a wide range of industrial and commercial applications. Due to their extreme environmental persistence, PFAS have the potential to bioaccumulate, cause adverse effects, and present challenges regarding remediation. Recently, microbial and enzymatic reactions for sustainable degradation of PFAS have gained attention from researchers, although biological decomposition of PFAS remains challenging. Surprisingly, laccases, the multi-copper oxidases produced by various organisms, showed potential for PFAS degradation. Mediators play key roles in initiating laccase induced PFAS degradation and defluorination reactions. The laccase-catalyzed PFAS degradation reactions are relatively slower than normal biocatalytic reactions and the low activity of native laccases constrains their capacity to complete defluorination. With their low redox potential and narrow substrate scope, an innovative remediation strategy must be taken to accelerate this reaction. In this review we have summarized the status, challenges, and future perspectives of enzymatic PFAS degradation. The knowledge of laccase-based defluorination and the molecular basis of the reaction mechanisms overviewed in this study could inform future applications of laccases for sustainable PFAS remediation.

Defluorination Mechanisms and Real-Time Dynamics of Per- and Polyfluoroalkyl Substances on Electrified Surfaces

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants found in groundwater sources and a wide variety of consumer products. In recent years, electrochemical approaches for the degradation of these harmful contaminants have garnered a significant amount of attention due to their efficiency and chemical-free modular nature. However, these electrochemical processes occur in open, highly non-equilibrium systems, and a detailed understanding of PFAS degradation mechanisms in these promising technologies is still in its infancy. To shed mechanistic insight into these complex processes, we present the first constant-electrode potential (CEP) quantum calculations of PFAS degradation on electrified surfaces. These advanced CEP calculations provide new mechanistic details about the intricate electronic processes that occur during PFAS degradation in the presence of an electrochemical bias, which cannot be gleaned from conventional density functional theory calculations. We complement our CEP calculations with large-scale ab initio molecular dynamics simulations in the presence of an electrochemical bias to provide time scales for PFAS degradation on electrified surfaces. Taken together, our CEP-based quantum calculations provide critical reaction mechanisms for PFAS degradation in open electrochemical systems, which can be used to prescreen candidate material surfaces and optimal electrochemical conditions for remediating PFAS and other environmental contaminants.

Rapid capture of perfluorooctanoic acid and perfluorooctane sulfonate at environmentally relevant concentrations via the 'mesh trap' of triazine-based polymer network: Mechanism and photocatalytic regeneration

Per- and polyfluoroalkyl substances (PFAS) pose a serious threat to groundwater (GW) environment worldwide due to their difficulty in removal and high toxicity. In this study, the 'mesh trap' of triazine-based polymerization network (SNW-1) demonstrated rapid capture performance for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) at environmentally relevant concentrations (1 μg/L). The SNW-1 can remove more than 90 % of PFOA and PFOS within 300 s and still maintain superior performance under four common GW anions and different [pH]0 (3 - 10). The removal degree of PFOA and PFOS is almost undetectable without SNW-1 dosage. Theoretical calculations were used to simulate the adsorption process and interfacial reaction mechanism in SNW-1/PFOA (Eads = -1.6717 eV) and SNW-1/PFOS (Eads = -1.2695 eV) systems. The adsorption of SNW-1/PFOA is stronger than SNW-1/PFOS. The typical van der Waals weak interactions between SNW-1 and PFOA were confirmed, which is slightly stronger than SNW-1/PFOS. In addition, SNW-1 regeneration in this paper was achieved in a photocatalytic activated peroxydisulfate (PDS) system which was different with previous reports. The desorption rates of PFOA and PFOS adsorbed on the surface of SNW-1 and the defluorination rate in the photocatalytic regeneration system were also tested. The photocatalytic regeneration mechanism between SNW-1 and PDS was electron transfer. And the electron transfer can be divided into three stages: strong adsorption of SNW-1/PDS (Eads = -2.1618 eV), electron transfer from SNW-1 to PDS and PDS cleavage. This study has a broad application prospect in the field of in-situ rapid resistance control of GW in PFAS contaminated sites and provides a theoretical support for environmentally friendly adsorbent regeneration technology.

Promoting SO4·- and ·OH Generation from Sulfate Solution toward Efficient Electrochemical Oxidation of Organic Contaminants at a B/N-Doped Diamond Flow-Through Electrode

Electrochemical oxidation via in situ-generated reactive oxygen species (ROS) is effective for the mineralization of refractory organic pollutants. However, the oxidation performance is usually limited by the low yield and utilization efficiency of ROS. Herein, a B/N-doped diamond (BND) flow-through electrode with enhanced SO4·-/·OH generation and utilization was designed for electrochemical oxidation of organic pollutants in sulfate solution. Both its SO4·-/·OH yields and SO4·- selectivity were improved by regulating B/N doping, and the production and utilization of SO4·-/·OH were facilitated by flow-through mode. BND showed fast PFOA oxidation with kinetic constants of 2.56-4.58 h-1 at low current densities of 2.0-5.0 mA cm-2. Its energy consumption for PFOA oxidation was 2.15-6.46 kWh m-3, which was lower than those of state-of-the-art electrodes under similar conditions. The BND anode was also efficient for treating organic fluorine wastewater and coking wastewater. The superior performance was contributed by its enhanced SO4·-/·OH yields and utilization, as well as high SO4·- selectivity.

Silicate-Confined Hydrogen on Nanoscale Zerovalent Iron for Efficient Defluorination Reactions

Defluorination reactions are increasingly vital due to the extensive use of organofluorine compounds with robust carbon-fluorine (C-F) bonds; particularly, the efficient defluorination of widespread and persistent per- and polyfluoroalkyl substances under mild conditions is crucial due to their accumulation in the environment and human body. Herein, we demonstrate that surface-modified silicate of pronounced proton affinity can confine active hydrogen (•H) onto nanoscale zerovalent iron (nZVI) by withdrawing electrons from nZVI to react with bound protons, generating confined active hydrogen (•H*) for efficient defluorination under ambient conditions. The exposed silicon cation (Siσ+) of silicate functions as a Lewis acid site to activate the C-F bond by forming Siσ+...F--C and substantially lowers the energy barrier of nucleophilic •H* attack, thereby facilitating selective C-F hydrodefluorination and subsequent fluorine immobilization. In a column flow reactor, silicate-modified nZVI efficiently removes perfluorooctanoic acid (PFOA) of concentrations ranging from 0.24 to 24 μmol/L with 75-92% defluorination efficiencies, 8 times higher than those of nZVI, generating environmentally friendly alkyl carboxylic acids as the primary products. Besides PFOA, this novel nZVI also realizes deep defluorination of other organofluorine compounds, including perfluorooctanesulfonates and fluoroquinolones, demonstrating its superior defluorination potential.

PFAS Destruction and Near-Complete Defluorination of Undiluted Aqueous Film-Forming Foams at Ambient Conditions by Piezoelectric Ball Milling

The nonthermal destruction of aqueous film-forming foam (AFFF) stockpiles, one of the major culprits responsible for water and soil contamination by per- and polyfluoroalkyl substances (PFAS), is extremely challenging because of the coexistence of mixed recalcitrant PFAS and complicated organic matrices at extremely high concentrations. To date, the complete defluorination of undiluted AFFF at ambient conditions has not been demonstrated. This study reports a novel piezoelectric ball milling approach for treating AFFF with a total organic fluorine concentration of 9080 mg/L and total organic carbon of 234 g/L. Near-complete defluorination (>95% conversion of organofluorine to fluoride) of undiluted AFFF was achieved by comilling with boron nitride. By carefully examining the experimental data, we identified AFFF liquid film thickness (Z) at the collision interface as a descriptor of treatment performance. We further validated that effective defluorination proceeded when Z was less than the criteria value of 2.3 μm. In light of this new understanding, the addition of SiO2 as a dispersant and the pre-evaporation solvents to reduce Z have been validated as effective strategies to promote AFFF treatment capacity.

Aging of Polystyrene Micro/Nanoplastics Enhances Cephalosporin Phototransformation via Structure-Sensitive Interfacial Hydrogen Bonding

Beyond their roles in adsorbing and transporting pollutants, microplastics (MPs) and nanoplastics (NPs), particularly polystyrene variants (PS-M/NPs), have emerged as potential accelerators for the transformation of coexisting contaminants. This study uncovered a novel environmental phenomenon induced by aged PS-M/NPs and delved into the underlying mechanisms. Our findings revealed that the aged PS-M/NP particles significantly amplified the photodegradation of common cephalosporin antibiotics, and the extent of enhancement was tightly correlated to the molecular structures of cephalosporin antibiotics. Notably, the results confirmed that the hydroxyl radical (OH•) acted as the primary agent to drive the accelerated degradation. Furthermore, in-depth analysis utilizing in situ Fourier transform infrared spectroscopy, batch adsorption experiments, and theoretical calculations underscored that the structure-dependent enhancement stemmed from the specific hydrogen bonding sites, rather than mere adsorption capacity. Specifically, the -OOH group (hydroperoxyl group) on the PS surface exhibited a greater potential to generate OH• compared to the -OH group. Therefore, cephalosporins that formed hydrogen bonds with -OOH moieties on the aged PS surfaces, as opposed to -OH, would experience a more pronounced degradation enhancement. Thus, the unique interaction pattern between contaminants and PS-M/NPs transforms aged PS into a selective reactor, facilitating the targeted degradation of pharmaceuticals in aquatic ecosystems.

PFAS in landfill leachate: Practical considerations for treatment and characterization

Per- and polyfluoroalkyl substances (PFAS) are widely used in consumer products and are particularly high in landfill leachate. The practice of sending leachate to wastewater treatment plants (WWTPs) is an issue for utilities that have biosolids land application limits based on PFAS concentrations. Moreover, landfills may face their own effluent limit guidelines for PFAS. The purpose of this review is to understand the most appropriate treatment technology combinations for mitigating PFAS in landfill leachate. The first objective is to understand the unique chemical characteristics of landfill leachate. The second objective is to establish the role and importance of known and emerging analytical techniques for PFAS characterization in leachate, including quantification of precursor compounds. Next, an overview of technologies that concentrate PFAS and technologies that destroy PFAS is provided, including fundamental background content and key operating parameters. Finally, practical considerations for PFAS treatment technologies are reviewed, and recommendations for PFAS treatment trains are described. Both pros and cons of treatment trains are noted. In summary, the complex matrix of leachate requires a separation treatment step first, such as foam fractionation, for example, to concentrate the PFAS into a lower-volume stream. Then, a degradation treatment step can be applied to the concentrated PFAS stream.

Unravel the in-Source Fragmentation Patterns of Per- and Polyfluoroalkyl Substances during Analysis by LC-ESI-HRMS

In-source fragmentation (ISF) was inevitable during electrospray ionization (ESI) of per- and polyfluoroalkyl substances (PFAS) when analyzed by liquid chromatography coupled with mass spectrometry (LC-MS), resulting in reduced response of molecular ions and misannotation of MS features. Herein, we analyzed 82 PFAS across 12 classes to systematically identify the structures with ISF potentials and reveal the fragmentation pathways. We found up to 100% ISF for 38 PFAS in six classes, which all contain the carboxylate (CO2-) headgroup, including perfluoro(di)carboxylates (PF(di)CA), omega H/Cl substituted PFCA (ωH/Cl-PFCA), fluorotelomer carboxylates, and perfluoroalkyl ether carboxylates (PFECA). Seven ISF pathways were identified, including direct cleavage of C-CO2-, C-O, and C-C bonds and eliminations of HF/CO2HF through cyclic transition states by the mechanisms of β-elimination, McLafferty rearrangement, or H···F bridging. We found that the loss of CO2 is a prerequisite for most other pathways, explaining the absence of ISF for PFAS without a CO2- headgroup. The elevated bond dissociation energy of C-CO2- explained the reduced ISF for long-chain PFCA and ωH-PFCA. Raising the MS vaporizer and ion transfer tube temperatures significantly aggravated the ISF of most PFAS. These findings provide valuable references to inform the structural identification of PFAS and their degradation products.

Aerobic or anaerobic? Microbial degradation of per- and polyfluoroalkyl substances: A review

The widespread utilization of per- and polyfluoroalkyl substances (PFASs) as "forever chemicals" is posing significant environmental risks and adverse effects on human health. Microbial degradation (e.g., bacteria and fungi) has been identified as a cost-effective and environmentally friendly method for PFAS degradation. However, its degradation efficiency, biotransformation pathway, and microbial mechanism vary significantly under aerobic and anaerobic conditions. This review provides a comprehensive overview of the similarities and differences in PFAS microbial degradation by bacteria and fungi under different oxygen conditions. Initially, the efficiencies and metabolites of PFAS microbial degradation were compared under aerobic and anaerobic conditions, including perfluorinated and polyfluorinated compounds. Additionally, the microbial mechanisms of PFAS microbial degradation were obtained by summarizing key degrading microbes and enzymes. Finally, the comparisons between aerobic and anaerobic conditions in PFAS microbial degradation were provided, addressing the main challenges and proposing future research directions focused on seeking combined biodegradation techniques, exploring novel microbial species capable of degrading PFAS, and confirming complete biodegradation pathways. The understanding of PFAS microbial degradation in aerobic and anaerobic environments is crucial for providing potential solutions and future research efforts in dealing with these "forever chemicals".

Destruction of perfluorooctane sulfonic acid (PFOS) in gas sparging incorporated UV-indole reductive treatment system - Benefits and challenges

Ultraviolet (UV) reductive treatment systems that generate hydrated electrons (eaq-) have emerged as a promising technology for the destruction of chemically inert per- and polyfluoroalkyl substances (PFAS). Here, we report on the evaluation of an indole derivative-based UV reductive treatment system that utilizes the amphipathic properties of PFAS at the gas-water interface (via nitrogen (N2) sparging) for more energy-efficient destruction of perfluorooctane sulfonic acid (PFOS). Results from this work illustrated that N2 sparging within UV systems can enhance the degradation and defluorination of PFOS compared to non-sparged conditions, but their overall treatment efficiency is low to industry standard. The inadequate system performance is likely originated from the insufficient accumulation of electron sources at the gas-water interface and their low water solubility level. In addition, carbonate species, which are ubiquitous in natural water and commonly applied as buffers in UV reductive treatment systems, negatively impact PFOS defluorination when indole is the electron source. The species-specific quenching imposed by carbonate species (e.g., HCO3- > H2CO3*) indicates that naturally occurring constituents and varying reactor conditions can substantially influence the remediation of PFOS. Other notable findings in this work include: 1) gramine, a cationic indole derivative, was able to remove > 99 % PFOS mass via electrostatic interaction within 0.5 h of reaction, signifying the electron source's structural property importance in UV reductive treatment systems, and 2) energy consumption calculations showed indole species are less energy-efficient as electron sources for PFOS destruction comparing to sulfite-iodide, but performance tradeoffs exist in both systems. The results of this work revealed both the benefits and challenges of utilizing N2 sparging and indole derivatives in UV-PFAS reductive treatment processes and provided critical information needed to improve the prediction and design of similar PFAS destruction technologies.

Bioelectricity drives transformation of nitrogen and perfluorooctanoic acid in constructed wetlands: Performances and mechanisms

In this study, constructed wetland-microbial fuel cell (CW-MFC) filled with modified basalt fiber (MBF) via iron modification was utilized for treating perfluorooctanoic acid (PFOA) containing sewage. Results showed the significant promotion by bioelectricity on ammonium and total nitrogen by 7.80-8.14 %. Although such enhancement was suppressed by PFOA, higher removal was still observed with closed circuit, and PFOA removal also increased by 9.05 %. Bioelectricity contributed to enrichment of bacteria involved in nitrifying (Nitrospira and Ellin6067), denitrifying (like Thauera and Dechloromonas), iron redox (Geobacter), and sulfate-reducing (Desulfobacter), aligned with up-regulated of functional genes, including amoA, narG , napA, narK, narS, nrfA, sulp and sqr. Enrichment of autohydrogenotrophic and sulfide-oxidizing autotrophic denitrifiers, and nitrate dependent iron oxidation bacteria by bioelectricity all promoted denitrification. Moreover, bioelectricity boosted relative abundance of organic compounds degradation enzymes, such as dehydrogenase, decarboxylase, and dehalogenase, supporting the enhancement on PFOA removal. Generally, PFOA was converted to short-chain perfluorocarboxylic acids (PFCAs) via decarboxylation, hydroxylation, HF elimination, hydrolysis, F- elimination, C-C bond scission, and dehydration in CW-MFC. The final PFCAs-products determined was perfluorobutyric acid. This work estimated feasibility of treating PFOA containing sewage by CM-MFC, and offered new insights on enhancing mechanisms of nitrogen and PFOA conversion.

Influence of aqueous constituents on hexafluoropropylene oxide trimer acid (HFPO-TA) defluorination by UV/sulfite/iodide system

Hexafluoropropylene oxide trimer acid (HFPO-TA) is an emerging alternative to traditional perfluoroalkyl substances (PFASs), which is characterized by its biotoxicity and persistence. The UV/sulfite/iodide photo-induced hydrated electrons system can effectively degrade HFPO-TA under mild conditions. However, the effects of water quality on this system need to be urgently investigated. This study explored the impact of common aqueous constituents, such as Cl-, HCO3-, PO43- and humic acid (HA) on the defluorination efficiency of HFPO-TA by the UV/sulfite/iodide system. Results indicated that low concentrations of Cl- (<1.0 mM), PO43- (<0.01 mM), and HA (<1.0 mg/L) have little effect on defluorination efficiency. However, as concentrations increase, these constituents can interact with photosensitizers or reactive species within the system, leading to a decrease in defluorination efficiency. HCO3-, in their various solution states, can compete with HFPO-TA for the hydrated electron (eaq-) or engage directly with the photosensitizer, resulting in a hindrance to the defluorination capabilities of the system. Furthermore, it was identified that the components in Xiaoqing River, especially Cl- and HCO3-, could greatly inhibit the defluorination and degradation efficiency of HFPO-TA by the system. Pretreatment such as nanofiltration would effectively mitigate this problem.

Photo-reductive decomposition of perfluorooctane sulfonate (PFOS) and its common alternatives by UV/VUV/sulfite process: Mechanism, kinetic modeling, and water matrix effects

The present study investigated the photo-reduction of perfluorooctane sulfonate (PFOS) and its alternatives, focusing on decomposition mechanisms, active species involvement, the influence of background water constituents, and kinetic model development. The decomposition and defluorination rates followed the order of PFOS > PFHxS > 6:2 FTSA > PFBS, with shorter chains and CH2 linkers enhancing the resistance of PFOS alternatives against the attack of hydrated electrons (eaq-). Two primary pathways were identified during the photodegradation of PFAS: (i) H/F exchange at CF bonds with the lowest bond dissociation energies (BDEs) and (ii) functional group cleavage followed by short-chain PFCAs formation, with OH playing a crucial role in transforming intermediates. Adding iodide and elevated temperatures demonstrated a synergistic effect on PFBS decomposition and defluorination, with high temperatures promoting functional group cleavage as the preferred defluorination pathway. The study examined the impact of background water constituents in different aqueous environments, from surface waters to wastewater streams and ion-exchange brine concentrates. Chloride exhibited a concentration-based dual impact on the UV/VUV/sulfite process: promotive effects at low dosages (1-10 mM) by acting as a secondary eaq- mediator, and adverse effects at high dosages (20-500 mM) due to the scavenging effect of generated chlorine radicals (Cl). High ionic strength adversely affected eaq- quantum efficiency. Additionally, bicarbonate and natural organic matter (NOM) had opposing effects on PFOS photo-reduction, primarily through eaq- scavenging and pH alteration. Kinetic modeling revealed reaction rate constants of the studied PFAS with eaq- ranging from 1.8 × 106 to 1.3 × 109 M-1 s-1, corroborating the concentration profiles of active species and highlighting the reductive nature of sulfite-mediated processes.

Efficient photocatalytic decomposition of PFOA over BiOI1-x with low power LED light

In recent years, the academic community has shown significant interest in per- or polyfluoroalkyl compounds (PFAS) due to their challenging degradation and potential health risks. Photocatalysis has been investigated for PFAS decomposition due to its environmentally friendly nature. In this study, BiOI with abundant iodine vacancies was synthesized through solvothermal and calcination methods (referred to as BiOI1-x), and was used for PFAS degradation with a low power UV light source. Compared to pure BiOI, BIOI1-x showed higher photocatalytic activity towards PFOA (perfluorooctanoic acid). Within 5 h under 5 W LED light irradiation, the degradation rate of PFOA reached 51.9 % with BiOI1-x calcined at 440 °C (No significant degradation of PFAS was observed with pure BiOI). Capture experiments, electron paramagnetic resonance spectroscopy, and electrochemical experiments revealed that the main active species in the system were photogenerated holes, followed by hydroxyl radicals. Furthermore, the presence of iodine vacancies significantly improved the efficiency of charge carrier separation and enhanced the photocatalytic performance. Finally, a hypothetical degradation pathway for PFOA in this system was suggested. This study achieved efficient degradation of PFAS under low power LED light (5 W), emphasizing its significant practical importance in terms of energy conservation.

Sorption/desorption and degradation of long- and short-chain PFAS by anion exchange resin and UV/sulfite system

A combined sorption/desorption and UV/sulfite degradation process was investigated for achieving efficient elimination of PFAS from water. Two gel-type resins, Purolite A532E and A600, and one macroporous resin, Purolite A860, were firstly tested for the sorption of individual PFPrA, PFHxA, PFOA, PFOS, and GenX at different concentrations. Sorption data and density functional theory (DFT) calculations revealed that electrostatic interactions predominated for short-chain PFAS sorption and hydrophobic interactions played a more significant role for long-chain PFAS than for short-chain PFAS. A600 and A860 were selected for desorption tests with 0.025% NaOH, 5% NaCl, and 5% NH4Cl solution with or without 20% ethanol (EtOH) due to their high sorption capacity for all target PFAS. The mixture of 5% NH4Cl and 20% EtOH as the desorption solution typically showed the highest desorption efficiency. PFOS was the most resistant for desorption but its desorption could be enhanced by stronger mixing conditions (in 5% NaCl + 20% EtOH). Direct degradation of studied PFAS in the desorption solution (0.025% NaOH, 5% NaCl, and 5% NH4Cl) by UV/sulfite achieved 97.6-100% degradation and 46.6-86.1% defluorination. EtOH hindered degradation and thus should be separated from the water before UV/sulfite degradation.

Destruction of Per- and Polyfluoroalkyl Substances in Reverse Osmosis Concentrate Using UV-Advanced Reduction Processes

UV-advanced reduction processes (UV-ARP), characterized by the strongly reducing aqueous electron (eaq -), have been shown to degrade perfluoroalkyl and polyfluoroalkyl substances (PFAS). Due to the high cost of PFAS destruction technologies, concentrated waste streams derived from physical treatment processes, such as ion exchange or membrane concentrates, are promising targets for implementation of these technologies. However, there are limited studies on the application of UV-ARP for PFAS destruction in concentrated waste streams. This study evaluates the effectiveness of the UV/sulfite ARP in reverse osmosis concentrate (ROC) containing high concentrations of dissolved organic carbon (DOC), nitrate, and carbonate species, spiked with mg/L concentrations of perfluorooctanesulfonic acid, perfluorobutanesulfonic acid, perfluorooctanoic acid, and perfluorobutanoic acid. We demonstrate that hardness removal and preoxidation of ROC with UV/persulfate enables >90% PFAS defluorination within 24 h of subsequent UV/sulfite treatment, a 3-fold enhancement in defluorination % compared to UV/sulfite treatment without preoxidation. This enhancement is shown to result from abatement of the light shielding and eaq - scavenging capacity of DOC during UV/persulfate oxidation. Collectively, these results demonstrate that appropriate pretreatment steps increase the effectiveness of PFAS destruction using UV-ARP, supporting the application of UV-ARP for PFAS destruction in ROC and other concentrated waste streams.

Photocatalytic low-temperature defluorination of PFASs

Polyfluoroalkyl and perfluoroalkyl substances (PFASs) are found in many everyday consumer products, often because of their high thermal and chemical stabilities, as well as their hydrophobic and oleophobic properties1. However, the inert carbon-fluorine (C-F) bonds that give PFASs their properties also provide resistance to decomposition through defluorination, leading to long-term persistence in the environment, as well as in the human body, raising substantial safety and health concerns1-5. Despite recent advances in non-incineration approaches for the destruction of functionalized PFASs, processes for the recycling of perfluorocarbons (PFCs) as well as polymeric PFASs such as polytetrafluoroethylene (PTFE) are limited to methods that use either elevated temperatures or strong reducing reagents. Here we report the defluorination of PFASs with a highly twisted carbazole-cored super-photoreductant KQGZ. A series of PFASs could be defluorinated photocatalytically at 40-60 °C. PTFE gave amorphous carbon and fluoride salts as the major products. Oligomeric PFASs such as PFCs, perfluorooctane sulfonic acid (PFOS), polyfluorooctanoic acid (PFOA) and derivatives give carbonate, formate, oxalate and trifluoroacetate as the defluorinated products. This allows for the recycling of fluorine in PFASs as inorganic fluoride salt. The mechanistic investigation reveals the difference in reaction behaviour and product components for PTFE and oligomeric PFASs. This work opens a window for the low-temperature photoreductive defluorination of the 'forever chemicals' PFASs, especially for PTFE, as well as the discovery of new super-photoreductants.

Synergistic adsorption and UV degradation of perfluorooctanoic acid by amine-functionalized A-center sphalerite

Perfluorinated alkylated substances (PFAS), as a category of persistent organic pollutants, have garnered extensive concern due to their resilience against environmental degradation. Herein, we developed an amine-functionalized sphalerite (ZnS) with adjustable surface amine functional groups and Zn defects (ZnS-X%[N]) by in situ coprecipitation and simple hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB). This material demonstrated efficient PFAS adsorption and subsequent photo-induced degradation under UV irradiation. The characterization results by TEM, BET, FTIR, XPS and EPR revealed that CTAB primarily influences ZnS by modulating surface amine functionalities, zinc defect density, and enhancing its photoreductive capacity. Adsorption and kinetic degradation experiments further showed that a medium CTAB concentration in ZnS-40%[N] achieves highest PFAS adsorption capacity (Cmax: 0.201 mol kg-1), and the corresponding decomposition rate was the fastest (kde: 1.53; kdf: 1.19). This efficacy is attributed to the ZnS-40%[N]'s ideal adsorptive sites and surface shallow defects. Moreover, theoretical simulation also supports the above experimental inference. Overall, ZnS-X%[N] exhibits a synergistic effect on PFAS adsorption and degradation, showcasing its potential for environmental adaptability and practical application.

State of the science and regulatory acceptability for PFAS residual management options: PFAS disposal or destruction options

This systematic review covers the urgent challenges posed by per- and polyfluoroalkyl substances (PFAS) in managing residuals from municipal, industrial, and waste treatment sources. It covers regulatory considerations, treatment technologies, residual management strategies, and critical conclusions and recommendations. A rigorous methodology was employed, utilizing scientific search engines and a wide array of peer-reviewed journal articles, technical reports, and regulatory guidance, to ensure the inclusion of the most relevant and up-to-date information on PFAS management of impacted residuals. The increasing public and regulatory focus underscores the persistence and environmental impact of PFAS. Emerging technologies for removing and sequestrating PFAS from environmental media are evaluated, and innovative destruction methods for addressing the residual media and the concentrated waste streams generated from such treatment processes are reviewed. Additionally, the evolving regulatory landscape in the United States is summarized and insights into the complexities of PFAS in residual management are discussed. Overall, this systematic review serves as a vital resource to inform stakeholders, guide research, and facilitate responsible PFAS management, emphasizing the pressing need for effective residual management solutions amidst evolving regulations and persistent environmental threats.

Characterization of PFOA isomers from PFAS precursors and their reductive defluorination

Perfluorooctanoic acid (PFOA) including linear and branched isomers is one of only three PFAS included in the Stockholm convention on Persistent Organic Pollutants. Unfortunately, PFOA branched isomers have received less attention than the linear due to analytical difficulties and perceived lower environmental concentrations. In this study, we revealed a environmentally relevant pathway for the formation of branched PFOA from PFAS precursors. AFFF samples showed a doubling of branched PFOA concentrations (138 mg/L) after TOP assay oxidation (307 mg/L). These findings indicate that branched PFOA may be more pervasive in the environment than previously thought. Additionally, we investigated the reductive degradability of PFOA using vitamin B12 (VB12) (a naturally occurring electron shuttle) in combination with either zero-valent zinc (ZVZ) or zero-valent iron (ZVI). Linear PFOA, as well as two branched isomers (3-methyl PFOA and 5,5-dimethyl PFOA), resisted reductive defluorination under the experimental conditions. However, all other branched isomers degraded within 10 days in the ZVZ-VB12 system. The experimental rate constants for specific PFOA isomers generally correlate with their calculated reduction potentials, except for 6-methyl PFOA. A potential defluorination pathway was proposed based on high-resolution mass spectrometry (LC-Orbitrap) and density functional theory (DFT) studies.

Fundamental data for modeling electron-induced processes in plasma remediation of perfluoroalkyl substances

Plasma treatment of per- and polyfluoroalkyl substances (PFAS) contaminated water is a potentially energy efficient remediation method. In this treatment, an atmospheric pressure plasma interacts with surface-resident PFAS molecules. Developing a reaction mechanism and modeling of plasma-PFAS interactions requires fundamental data for electron-molecule reactions. In this paper, we present results of electron scattering calculations, potential energy landscapes and their implications for plasma modelling of a dielectric barrier discharge in PFAS contaminated gases, a first step towards modelling of plasma-water-PFAS intereactions. It is found that the plasma degradation of PFAS is dominated by dissociative electron attachment with the importance of other contributing processes varying depending on the molecule. All molecules posses a large number of shape resonances - transient negative ion states - from near-threshold up to ionization threshold. These states lie in the region of the most probable electron energies in the plasma (4-5 eV) and consequently are expected to further enhance the fragmentation dynamics in both dissociative attachment and dissociative excitation.

Multiphoton-Driven Photocatalytic Defluorination of Persistent Perfluoroalkyl Substances and Polymers by Visible Light

Perfluoroalkyl substances (PFASs) and fluorinated polymers (FPs) have been extensively utilized in various industries, whereas their extremely high stability poses environmental persistence and difficulty in waste treatment. Current decomposition approaches of PFASs and FPs typically require harsh conditions such as heating over 400 °C. Thus, there is a pressing need to develop a new technique capable of decomposing them under mild conditions. Here, we demonstrated that perfluorooctanesulfonate (PFOS), known as a "persistent chemical," and Nafion, a widely utilized sulfonated FP for ion-exchange membranes, can be efficiently decomposed into fluorine ions under ambient conditions via the irradiation of visible LED light onto semiconductor nanocrystals (NCs). PFOS was completely defluorinated within 8-h irradiation of 405-nm LED light, and the turnover number of the C-F bond dissociation per NC was 17200. Furthermore, 81 % defluorination of Nafion was achieved for 24-h light irradiation, demonstrating the efficient photocatalytic properties under visible light. We revealed that this decomposition is driven by cooperative mechanisms involving light-induced ligand displacements and Auger-induced electron injections via hydrated electrons and higher excited states. This study not only demonstrates the feasibility of efficiently breaking down various PFASs and FPs under mild conditions but also paves the way for advancing toward a sustainable fluorine-recycling society.

Rethinking alternatives to fluorinated pops in aqueous environment and corresponding destructive treatment strategies

Alternatives are being developed to replace fluorinated persistent organic pollutants (POPs) listed in the Stockholm Convention, bypass environmental regulations, and overcome environmental risks. However, the extensive usage of fluorinated POPs alternatives has revealed potential risks such as high exposure levels, long-range transport properties, and physiological toxicity. Therefore, it is imperative to rethink the alternatives and their treatment technologies. This review aims to consider the existing destructive technologies for completely eliminating fluorinated POPs alternatives from the earth based on the updated classification and risks overview. Herein, the types of common alternatives were renewed and categorized, and their risks to the environment and organisms were concluded. The efficiency, effectiveness, energy utilization, sustainability, and cost of various degradation technologies in the treatment of fluorinated POPs alternatives were reviewed and evaluated. Meanwhile, the reaction mechanisms of different fluorinated POPs alternatives are systematically generalized, and the correlation between the structure of alternatives and the degradation characteristics was discussed, providing mechanistic insights for their removal from the environment. Overall, the review supplies a theoretical foundation and reference for the control and treatment of fluorinated POPs alternatives pollution.

Per- and polyfluoroalkyl substances contamination of drinking water sources in Africa: Pollution sources and possible treatment methods

Despite the detection of poly- and perfluorinated alkyl substances (PFAS) in the water system in Africa, the effort towards mitigating PFAS in water in Africa needs to be better understood. Therefore, this review evaluated the contamination status and mitigation methods for handling PFAS-contaminated water systems in Africa. The findings revealed the presence of PFAS in wastewater treatment plant (WWTP) effluents, surface water and commercially available bottled and tap water in African countries. The concentration of PFAS in drinking water sources reviewed ranged from < limits of quantification to 778 ng L-1. The sources of PFAS in water systems in Africa are linked to uncontrolled importation of PFAS-containing products, WWTP effluents and inappropriate disposal of PFAS-containing materials. The information on treatment methods for PFAS-contaminated water systems is scanty. Unfortunately, the treatment method is challenged by poor water research infrastructure and facilities, lack of awareness, poor research funding and weak legislation; however, adsorption and membrane technology seem favourable for removing PFAS from water systems in Africa. It is essential to focus on monitoring and assessing drinking water quality in Africa to reduce the disease burden that this may cause. Most African countries' currently implemented water treatment facilities cannot efficiently remove PFAS during treatment. Therefore, governments in Africa need to fund more research to develop an efficient water treatment technique that is sustainable in Africa.

Carbon Adsorbent Properties Impact Hydrated Electron Activity and Perfluorocarboxylic Acid (PFCA) Destruction

Carbon-based adsorbents used to remove recalcitrant water contaminants, including perfluoroalkyl substances (PFAS), are often regenerated using energy-intensive treatments that can form harmful byproducts. We explore mechanisms for sorbent regeneration using hydrated electrons (eaq -) from sulfite ultraviolet photolysis (UV/sulfite) in water. We studied the UV/sulfite treatment on three carbon-based sorbents with varying material properties: granular activated carbon (GAC), carbon nanotubes (CNTs), and polyethylenimine-modified lignin (lignin). Reaction rates and defluorination of dissolved and adsorbed model perfluorocarboxylic acids (PFCAs), perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), were measured. Monochloroacetic acid (MCAA) was employed to empirically quantify eaq - formation rates in heterogeneous suspensions. Results show that dissolved PFCAs react rapidly compared to adsorbed ones. Carbon particles in solution decreased aqueous reaction rates by inducing light attenuation, eaq - scavenging, and sulfite consumption. The magnitude of these effects depended on adsorbent properties and surface chemistry. GAC lowered PFOA destruction due to strong adsorption. CNT and lignin suspensions decreased eaq - formation rates by attenuating light. Lignin showed high eaq - quenching, likely due to its oxygenated functional groups. These results indicate that desorbing PFAS and separating the adsorbent before initiating PFAS degradation reactions will be the best engineering approach for adsorbent regeneration using UV/sulfite.

Enhanced perfluorooctanoic acid (PFOA) degradation by electrochemical activation of peroxydisulfate (PDS) during electrooxidation for water treatment

Improved treatment of per- and polyfluoroalkyl substances (PFAS) in water is critically important in light of the proposed United States Environmental Protection Agency (USEPA) drinking water regulations at ng L-1 levels. The addition of peroxymonosulfate (PMS) during electrooxidation (EO) can remove and destroy PFAS, but ng L-1 levels have not been tested, and PMS itself can be toxic. The objective of this research was to test peroxydisulfate (PDS, an alternative to PMS) activation by boron-doped diamond (BDD) electrodes for perfluorooctanoic acid (PFOA) degradation. The influence of PDS concentration, temperature, and environmental water matrix effects, and PFOA concentration on PDS-EO performance were systematically examined. Batch reactor experiments revealed that 99 % of PFOA was degraded and 69 % defluorination was achieved, confirming PFOA mineralization. Scavenging experiments implied that sulfate radicals (SO4-) and hydroxyl radicals (HO) played a more important role for PFOA degradation than 1O2 or electrons (e-). Further identification of PFOA degradation and transformation products by liquid chromatography-mass spectrometry (LC-MS) analysis established plausible PFOA degradation pathways. The analysis corroborates that direct electron transfers at the electrode initiate PFOA oxidation and SO4- improves overall treatment by cleaving the CC bond between the C7F15 and COOH moieties in PFOA, leading to possible products such as C7F15 and F-. The perfluoroalkyl radicals can be oxidized by SO4- and HO, resulting in the formation of shorter chain perfluorocarboxylic acids (e.g., perfluorobutanoic acid [PFBA]), with eventual mineralization to CO2 and F-. At an environmentally relevant low initial concentration of 100 ng L-1 PFOA, 99 % degradation was achieved. The degradation of PFOA was slightly affected by the water matrix as less removal was observed in an environmental river water sample (91 %) compared to tests conducted in Milli-Q water (99 %). Overall, EO with PDS provided a destructive approach for the elimination of PFOA.

Efficient degradation of F-53B as PFOS alternative in water by plasma discharge: Feasibility and mechanism insights

The frequent detection of 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) in various environments has raised concerns owing to its comparable or even higher environmental persistence and toxicity than perfluorooctane sulfonate (PFOS). This study investigated the plasma degradation of F-53B for the first time using a water film plasma discharge system. The results revealed that F-53B demonstrated a higher rate constant but similar defluorination compared to PFOS, which could be ascribed to the introduction of the chlorine atom. Successful elimination (94.8-100 %) was attained at F-53B initial concentrations between 0.5 and 10 mg/L, with energy yields varying from 15.1 to 84.5 mg/kWh. The mechanistic exploration suggested that the decomposition of F-53B mainly occurred at the gas-liquid interface, where it directly reacted with reactive species generated by gas discharge. F-53B degradation pathways involving dechlorination, desulfonation, carboxylation, C-O bond cleavage, and stepwise CF2 elimination were proposed based on the identified byproducts and theoretical calculations. Furthermore, the demonstrated effectiveness in removing F-53B in various coexisting ions and water matrices highlighted the robust anti-interference ability of the treatment process. These findings provide mechanistic insights into the plasma degradation of F-53B, showcasing the potential of plasma processes for eliminating PFAS alternatives in water.

Structural investigation of the complexation between vitamin B12 and per- and polyfluoroalkyl substances: Insights into degradation using density functional theory

Environmental remediation of per- and polyfluoroalkyl substances (PFAS) has become a significant research topic in recent years due to the fact that these materials are omnipresent, resistant to degradation and thus environmentally persistent. Unfortunately, they have also been shown to cause health concerns. PFAS are widely used in industrial applications and consumer products. Vitamin B12 (B12) has been identified as being catalytically active towards a variety of halogenated compounds such as PFAS. It has also been shown to be effective when using sulfide as a reducing agent for B12. This is promising as sulfide is readily available in the environment. However, there are many unknowns with respect to PFAS interactions with B12. These include the reaction mechanism and B12's specificity for PFAS with certain functionalization(s). In order to understand the specificity of B12 towards branched PFAS, we examined the atomistic interactions between B12 and eight different PFAS molecules using Density Functional Theory (B3LYP/cc-pVDZ). The PFAS test set included linear PFAS and their branched analogs, carboxylic acid and sulfonic acid headgroups, and aromatic and non-aromatic cyclic structures. Conformational analyses were carried out to determine the lowest energy configurations. This analysis showed that small chain PFAS such as perfluorobutanoic acid interact with the cobalt center of B12. Bulkier PFAS prefer to interact with the amine and carbonyl groups on the sidechains of the B12 ring system. Furthermore, computed complexation energies determined that, in general, branched PFAS (e.g. perfluoro-5-methylheptane sulfonic acid) interact more strongly than linear molecules (e.g. perfluorooctanesulfonic acid). Our results indicate that it may be possible to alter the interactions between B12 and PFAS by synthetically modifying the sidechains of the ring structure.

Emergency of per- and polyfluoroalkyl substances in drinking water: Status, regulation, and mitigation strategies in developing countries

The detection of per- and polyfluoroalkyl substances (PFAS) in water presents a significant challenge for developing countries, requiring urgent attention. This review focuses on understanding the emergence of PFAS in drinking water, health concerns, and removal strategies for PFAS in water systems in developing countries. This review indicates the need for more studies to be conducted in many developing nations due to limited information on the environmental status and fate of PFAS. The health consequences of PFAS in water are enormous and cannot be overemphasized. Efforts are ongoing to legislate a national standard for PFAS in drinking water. Currently, there are few known mitigation efforts from African countries, in contrast to several developing nations in Asia. Therefore, there is an urgent need to develop economically viable techniques that could be integrated into large-scale operations to remove PFAS from water systems in the region. However, despite the success achieved with removing long-chain PFAS from water, more studies are required on strategies for eliminating short-chain moieties in water.

Enhanced sorption and destruction of PFAS by biochar-enabled advanced reduction process

The biochar-enabled advanced reduction process (ARP) was developed for enhanced sorption (by biochar) and destruction of PFAS (by ARP) in water. First, the biochar (BC) was functionalized by iron oxide (Fe3O4), zero valent iron (ZVI), and chitosan (chi) to produce four biochars (BC, Fe3O4-BC, ZVI-chi-BC, and chi-BC) with improved physicochemical properties (e.g., specific surface area, pore structure, hydrophobicity, and surface functional groups). Batch sorption experimental results revealed that compared to unmodified biochar, all modified biochars showed greater sorption efficiency, and the chi-BC performed the best for PFAS sorption. The chi-BC was then selected to facilitate reductive destruction and defluorination of PFAS in water by ARP in the UV-sulfite system. Adding chi-BC in UV-sulfite ARP system significantly enhanced both degradation and defluorination efficiencies of PFAS (up to ∼100% degradation and ∼85% defluorination efficiencies). Radical analysis using electron paramagnetic resonance (EPR) spectroscopy showed that sulfite radicals dominated at neutral pH (7.0), while hydrated electrons (eaq-) were abundant at higher pH (11) for the efficient destruction of PFAS in the ARP system. Our findings elucidate the synergies of biochar and ARP in enhancing PFAS sorption and degradation, providing new insights into PFAS reductive destruction and defluorination by different reducing radical species at varying pH conditions.