Rapid photochemical decomposition of perfluorooctanoic acid mediated by a comprehensive effect of nitrogen dioxide radicals and Fe3+/Fe2+ redox cycle

Photoinduced oxidation of chromium picolinate to hexavalent chromium in the presence of ferric ions

The occurrence of chromium picolinate (Cr(pic)3) in environment has attracted raising concerns on its fate and the associated risks. Herein, the photoinduced oxidation of Cr(pic)3 in the presence of ferric ions (Fe(III)) under simulated sunlight and natural solar light irradiation were investigated. Cr(pic)3 was stable under dark or without Fe(III). 87.9 % of Cr(pic)3 (C0 = 1.0 μM) was degraded in the presence of 50 μM Fe(III) after 90 min simulated sunlight irradiation at initial pH of 4.0. •OH was the main cause for Cr(pic)3 oxidation, it attacked the chromium center to generate hexavalent chromium (Cr(VI)) and picolinic acid (k = 5.9 ×108 M-1·s-1). Picolinic acid could be further oxidized to NH4+ and small organics. Relative higher Fe(III) content (25 - 75 μM) and Cr(pic)3 concentration (0.5 - 2.0 μM) promoted both of Cr(pic)3 degradation and Cr(VI) accumulation. While, the degradation of Cr(pic)3 decreased with pH at the range of 3.0 - 8.0, more Cr(VI) was accumulated at pH 5.0 and 6.0. The co-existence of inorganic ions and dissolved organic matter (DOM) in river water inhibited Cr(pic)3 oxidation by scavenging the •OH formed and shielding the light. 8.0 - 16.7 μg/L of Cr(VI) was accumulated after 9.0 h simulated sunlight irradiation of Cr(pic)3 in river water matrix ([Fe(III)]0 = 50 - 100 μM). The generation of Cr(VI) under solar light was slower than that under simulated sunlight due to the weaker light intensity (43.2 - 85.0 mW/cm2 vs. 750 - 1300 mW/cm2). These results consistently suggest photoinduced oxidation of Cr(pic)3 in environment generates the toxic Cr(VI), which deserves significant attention.

Solar Photodegradation of a Novel des-F(6)-Fluoroquinolone, Garenoxacin, and Ecotoxicity of Its Phototransformation Products

Garenoxacin (GRNX) is a novel des-F(6)-fluoroquinolone on the horizon; thus, its fate and risk in the aquatic environment deserve attention. This study systematically investigated, for the first time, the phototransformation of GRNX under simulated and natural sunlight and assessed the ecotoxicity of its photodegradation products. Phototransformation of GRNX was observed to depend strongly on its ionization state, with direct photolysis and self-sensitized photolysis having comparable contributions for the cationic and zwitterionic species, while the latter dominated for the anionic species. Singlet oxygen generated via the self-sensitized photolysis of GRNX was the major reactive oxygen species in its photodegradation. Phototransformation of GRNX in different ionization states followed distinct pathways, with defluorination of the difluoromethyl group occurring only for the zwitterionic and anionic species. GRNX photodegradation in natural water could be described by a simple kinetic model based on the measured steady-state concentrations of 1O2 and ·OH. Toxicity tests with Vibrio fischeri and Chlorella vulgaris consistently indicate that the generation of hydroxylation and decarboxylation products during photodegradation of GRNX increased the acute toxicity. These findings not only provide insights into the fate of GRNX in sunlit surface water but also reveal the potentially significant risk of its photodegradation products to the aquatic ecosystem.

PFHpA alters lipid metabolism and increases the risk of metabolic dysfunction-associated steatotic liver disease in youth-a translational research framework

To address the growing epidemic of liver disease, particularly in pediatric populations, it is crucial to identify modifiable risk factors for the development and progression of metabolic dysfunction-associated steatotic liver disease (MASLD). Per- and polyfluoroalkyl substances (PFAS) are persistent ubiquitous chemicals and have emerged as potential risk factors for liver damage. However, their impact on the etiology and severity of MASLD remains largely unexplored in humans. This study aims to bridge the gap between human and in vitro studies to understand how exposure to perfluoroheptanoic acid (PFHpA), one of the emerging PFAS replacements which accumulates in high concentrations in the liver, contributes to MASLD risk and progression. First, we showed that PFHpA plasma concentrations were significantly associated with increased risk of MASLD in obese adolescents. Further, we examined the impact of PFHpA on hepatic metabolism using 3D human liver spheroids and single-cell transcriptomics to identify major hepatic pathways affected by PFHpA. Next, we integrated the in vivo and in vitro multi-omics datasets with a novel statistical approach which identified signatures of proteins and metabolites associated with MASLD development triggered by PFHpA exposure. In addition to characterizing the contribution of PFHpA to MASLD progression, our study provides a novel strategy to identify individuals at high risk of PFHpA-induced MASLD and develop early intervention strategies. Notably, our analysis revealed that the proteomic signature exhibited a stronger correlation between both PFHpA exposure and MASLD risk compared to the metabolomic signature. While establishing a clear connection between PFHpA exposure and MASLD progression in humans, our study delved into the molecular mechanisms through which PFHpA disrupts liver metabolism. Our in vitro findings revealed that PFHpA primarily impacts lipid metabolism, leading to a notable increase of lipid accumulation in human hepatocytes after PFHpA exposure. Among the pathways involved in lipid metabolism in hepatocytes, regulation of lipid metabolism by PPAR-a showed a remarkable activation. Moreover, the translational research framework we developed by integrating human and in vitro data provided us biomarkers to identify individuals at a high risk of MASLD due to PFHpA exposure. Our framework can inform policies on PFAS-induced liver disease and identify potential targets for prevention and treatment strategies.

Insights into the effect of nitrate photolysis on short-chain fatty acids production from waste activated sludge in anaerobic fermentation system: Performance and mechanisms

Nitrate photolysis has become an efficient, low-cost and promising technology for emerging contaminants removal, while its performance and mechanism for waste activated sludge (WAS) treatment is still unknown. This study innovatively introduced nitrate photolysis for WAS disintegration, and investigated the effect of nitrate addition (150-375 mg N/L) for short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF). The results showed that nitrate photolysis significantly promoted the SCFAs production from WAS, and peaked at 280.7 mg/g VSS with 7-d fermentation with 150 mg N/L addition (150N-UV), which increased by 8.8-35.0 % and 10.7-23.3 % compared with other photolysis groups and sole nitrate groups. Effective release of the soluble organics was observed in the nitrate photolysis groups during AF, especially soluble proteins, reaching 1505.4 mg COD/L at 9 d in 150N-UV group, promoted by 7.0∼15.7 % than nitrate/nitrate photolysis groups. The model compounds simulation experiment further demonstrated the positive effect of nitrate photolysis on organics hydrolysis and SCFAs accumulation. The result of the radical capture and quenching verified the reactive oxygen species contributed more compared with reactive nitrogen species. Functional group analysis confirmed the effective bioconversion of the macromolecular organics during the fermentation. Moreover, the nitrate photolysis enhanced the enrichment of the functional consortia, including anaerobic fermentation bacteria (AFB), e.g., Fnoticella, Romboutsia, Gracilibacter and Sedimentibacter, and nitrate reducing bacteria (NRB), e.g., Acinerobacter and Ahniella. The macrogenetic analysis further revealed that glycolysis, amino acid metabolism, acetate metabolism and nitrogen metabolism were the dominating metabolic pathways during fermentation, and the abundance of the relevant genes were enhanced in 150N-UV group.

Current state of knowledge of environmental occurrence, toxic effects, and advanced treatment of PFOS and PFOA

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic synthetic compounds, with high chemical and thermal stability and a persistent, stable and bioaccumulative nature that renders them a potential hazard for the environment, its organisms, and humans alike. Perfluorooctane sulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) are the most well-known substances of this category and even though they are phased out from production they are still highly detectable in several environmental matrices. As a result, they have been spread globally in water sources, soil and biota exerting toxic and detrimental effects. Therefore, up and coming technologies, namely advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are being tested for their implementation in the degradation of these pollutants. Thus, the present review compiles the current knowledge on the occurrence of PFOS and PFOA in the environment, the various toxic effects they have induced in different organisms as well as the ability of AOPs and ARPs to diminish and/or eliminate them from the environment.

Significantly Accelerated Photochemical Perfluorooctanoic Acid Decomposition at the Air-Water Interface of Microdroplets

The efficient elimination of per- and polyfluoroalkyl substances (PFASs) from the environment remains a huge challenge and requires advanced technologies. Herein, we demonstrate that perfluorooctanoic acid (PFOA) photochemical decomposition could be significantly accelerated by simply carrying out this process in microdroplets. The almost complete removal of 100 and 500 μg/L PFOA was observed after 20 min of irradiation in microdroplets, while this was achieved after about 2 h in the corresponding bulk phase counterpart. To better compare the defluorination ratio, 10 mg/L PFOA was used typically, and the defluorination rates in microdroplets were tens of times faster than that in the bulk phase reaction system. The high performances in actual water matrices, universality, and scale-up applicability were demonstrated as well. We revealed in-depth that the great acceleration is due to the abundance of the air-water interface in microdroplets, where the reactants concentration enrichment, ultrahigh interfacial electric field, and partial solvation effects synergistically promoted photoreactions responsible for PFOA decomposition, as evidenced by simulated Raman scattering microscopy imaging, vibrational Stark effect measurement, and DFT calculation. This study provides an effective approach and highlights the important roles of air-water interface of microdroplets in PFASs treatment.

The Specific Removal of Perfluorooctanoic Acid Based on Pillar[5]arene-Polymer-Packed Nanochannel Membrane

The conspicuous surface activity and exceptional chemical stability of perfluorooctanoic acid, commonly referred to as PFOA, have led to its extensive utilization across a broad spectrum of industrial and commercial products. Nonetheless, significant concerns have arisen regarding the environmental presence of PFOAs, driven by their recognized persistence, bioaccumulative nature, and potential human health risks. In the realm of sustainable agriculture, a pivotal challenge revolves around the development of specialized materials capable of effectively and selectively eliminating PFOA from the environment. This study proposes harnessing the exceptional properties of a pillar[5]arene polymer to construct a nanochannel membrane filled with tryptophan-alanine dipeptide pillar[5]arene polymer. Through the functionalization of these nanochannel membranes, we achieved a PFOA removal rate of 0.01 mmol L-1 min-1, surpassing the rates observed with other control chemicals by a factor of 4.5-15. The research on PFOA removal materials has been boosted because of the creation of this highly selective PFOA removal membrane.

Research Updates on the Mechanism and Influencing Factors of the Photocatalytic Degradation of Perfluorooctanoic Acid (PFOA) in Water Environments

Perfluorooctanoic acid is ubiquitous in water bodies and is detrimental to the health of organisms. Effectively removing perfluorooctanoic acid (PFOA), a persistent organic pollutant, has been a hot topic around the world. With traditional physical, chemical, and biological methods, it is difficult to effectively and completely remove PFOA, the costs are high, and it is easy to cause secondary pollution. There are difficulties in applying some technologies. Therefore, more efficient and green degradation technologies have been sought. Photochemical degradation has been shown to be a low-cost, efficient, and sustainable technique for PFOA removal from water. Photocatalytic degradation technology offers great potential and prospects for the efficient degradation of PFOA. Most studies on PFOA have been conducted under ideal laboratory conditions at concentrations that are higher than those detected in real wastewater. This paper summarizes the research status of the photo-oxidative degradation of PFOA, and it summarizes the mechanism and kinetics of PFOA degradation in different systems, as well as the influence of key factors on the photo-oxidative degradation and defluoridation process, such as system pH, photocatalyst concentration, etc. PFOA photodegradation technology's existing problems and future work directions are also presented. This review provides a useful reference for future research on PFOA pollution control technology.

Nitrate promoted defluorination of perfluorooctanoic acid in UV/sulfite system: Coupling hydrated electron/reactive nitrogen species-mediated reduction and oxidation

A significantly accelerated defluorination of recalcitrant perfluorooctanoic acid (PFOA) was explored with the co-present nitrate (20 mg L^-1) by UV/sulfite treatment (UV/sulfite-nitrate). The deep defluorination of PFOA and complete denitrification of nitrate were simultaneously achieved in UV/sulfite-nitrate system. At the initial 30 min, PFOA defluorination exhibited an induction period, exactly corresponding to the removal of the co-existed nitrate. Upon the induction period passed, an accelerated removal of PFOA (5 mg L^-1) occurred, nearly 100% defluorination ratio reached within 2 h. Compared with those in UV/sulfite, the kinetics of PFOA decay, defluorination, and transformation product formations were greatly enhanced in UV/sulfite-nitrate system. Reactive nitrogen species (RNS) generated from e_aq^--induced reduction of nitrate were found to play significant roles on the promoted defluorination apart from e_aq^--mediated reductive defluorination. The investigations on solution pH (7.0-11.0) confirmed that the reductive defluorination of PFOA was more efficient under alkaline conditions, however, the presence of nitrate can promote the defluorination even under neutral pH. Theoretical calculations of Fukui function demonstrated that RNS could easily launch electrophilic attack toward H-rich moieties of fluorotelomer carboxylates (FTCAs, C_nF_2n+1-(CH₂)_m-COO^-), more persistent intermediates (formed via H/F exchange), and convert FTCAs into shorter-chain perfluorinated carboxylic acids, thus facilitating the deep defluorination. Along with the analysis on the denitrification products, the liberation of fluoride ions and generated intermediates, possible decomposition pathways were proposed. This work highlights the indispensable synergy from e_aq^-/RNS with integrated reduction and oxidation on PFOA defluorination and will advance remediation technologies of perfluorinated compound contaminated water.

Photodegradation of per- and polyfluoroalkyl substances in water: A review of fundamentals and applications

Per- and polyfluoroalkyl substances (PFAS) are persistent, mobile, and toxic chemicals that are hazardous to human health and the environment. Several countries, including the United States, plan to set an enforceable maximum contamination level for certain PFAS compounds in drinking water sources. Among the available treatment options, photocatalytic treatment is promising for PFAS degradation and mineralization in the aqueous solution. In this review, recent advances in the abatement of PFAS from water using photo-oxidation and photo-reduction are systematically reviewed. Degradation mechanisms of PFAS by photo-oxidation involving the holes (h_vb⁺) and oxidative radicals and photo-reduction using the electrons (e_cb^-) and hydrated electrons (e_aq^-) are integrated. The recent development of innovative heterogeneous photocatalysts and photolysis systems for enhanced degradation of PFAS is highlighted. Photodegradation mechanisms of alternative compounds, such as hexafluoropropylene oxide dimer acid (GenX) and chlorinated polyfluorinated ether sulfonate (F-53B), are also critically evaluated. This paper concludes by identifying major knowledge gaps and some of the challenges that lie ahead in the scalability and adaptability issues of photocatalysis for natural water treatment. Development made in photocatalysts design and system optimization forges a path toward sustainable treatment of PFAS-contaminated water through photodegradation technologies.

Insight into UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) for p-arsanilic acid degradation and simultaneous arsenate immobilization

As a feed additive, p-arsanilic acid (p-ASA) is hardly metabolized in animal bodies and is excreted chemically unchanged via feces and urine, which can be transformed into more toxic inorganic arsenic species and other organic by-products upon degradation in the aquatic environment. In this study, UV-LED/persulfate (PS)/Fe(Ⅲ) and UV-LED/peroxymonosulfate (PMS)/Fe(Ⅲ) processes were developed to remove p-ASA and immobilize the formed inorganic arsenic via tuning solution pH. UV-LED/PMS/Fe(Ⅲ) (90.8%) presented the best performance for p-ASA degradation at pH 3.0, and the p-ASA degradation in these processes both followed the pseudo-first-order kinetics. The ∙OH played the major role in UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) systems. Solution pH greatly affected the p-ASA degradation and the maximum removal can be achieved at pH 3.0 due to the presence of more Fe(OH)(H₂O)₅²⁺. The dosages of Fe(III) and PMS (PS), SO₄^2- and HCO₃^- significantly influenced the performance of p-ASA oxidation, while HA, Cl^- and NO₃^- slightly affected the p-ASA degradation. According to quantum chemical calculation, radical addition on the C atom in the C-As bond of p-ASA was corroborated to be the dominant reaction pathway by SO₄∙^- and ∙OH. Additionally, the reactive sites and reasonable degradation pathways of p-ASA were proposed based on DFT calculation and HPLC/MS analysis. The release of inorganic arsenic in both processes can be effectively immobilized and the toxicity of the reaction solution dramatically reduced by adjusting solution pH to 6.0. UV-LED/PMS/Fe(Ⅲ) process was found to be more cost-effective than UV-LED/PS/Fe(Ⅲ) process at the low oxidant dosages.

A review of recent studies on toxicity, sequestration, and degradation of per- and polyfluoroalkyl substances (PFAS)

The fate, effects, and treatment of per- and polyfluoroalkyl substances (PFAS), an anthropogenic class of chemicals used in industrial and commercial production, are topics of great interest in recent research and news cycles. This interest stems from the ubiquity of PFAS in the global environment as well as their significant toxicological effects in humans and wildlife. Research on toxicity, sequestration, removal, and degradation of PFAS has grown rapidly, leading to a flood of valuable knowledge that can get swamped out in the perpetual rise in the number of publications. Selected papers from the Journal of Hazardous Materials between January 2018 and May 2022 on the toxicity, sequestration, and degradation of PFAS are reviewed in this article and made available as open-access publications for one year, in order to facilitate the distribution of critical knowledge surrounding PFAS. This review discusses routes of toxicity as observed in mammalian and cellular models, and the observed human health effects in exposed communities. Studies that evaluate of toxicity through in-silico approaches are highlighted in this paper. Removal of PFAS through modified carbon sorbents, nanoparticles, and anion exchange materials are discussed while comparing treatment efficiencies for different classes of PFAS. Finally, various biotic and abiotic degradation techniques, and the pathways and mechanisms involved are reviewed to provide a better understanding on the removal efficiencies and cost effectiveness of existing treatment strategies.

New insights into ferric iron-facilitated UV254 photolytic defluorination of perfluorooctanoic acid (PFOA): Combined experimental and theoretical study

UV/Fe³⁺-facilitated PFOA defluorination was often reported and recognized to proceed through a "ligand-to-metal charge transfer (LMCT)" mechanism in the literatures. Sufficient Fe³⁺ supply is important for sustaining the LMCT reaction pathway. In this study, an interesting "excessive defluorination" was observed, even the continuous Fe³⁺ supply was cut off, implying a parallel mechanism strengthening PFOA defluorination. Based the results of intermediate products detection, ¹⁹F NMR analysis, and exploration of electron density alternation, transition energy evolution, and bonds characteristics, remarkable electron density perturbation in [PFOA-Fe]²⁺ was revealed. This effect was triggered by the complexation between PFOA anion and Fe³⁺, diminishing electron shielding on the perfluorinated carbon chain. Hence, the dissociation energy of C-C bonds was reduced by maximally 53% (C4-C5). Once attacked by high-flux UV₂₅₄ photons, the perfluorinated carbon chain underwent scission, and subsequent defluorination was achieved via hydrolysis reactions. This parallel mechanism cooperated with the LMCT mechanism, leading to the observed "excessive defluorination." The degree of UV/Fe³⁺-synergized PFOA defluorination depended on UV₂₅₄ photon flux and Fe³⁺ dosage. High UV₂₅₄ intensity guaranteed fast defluorination kinetics. A [Fe³⁺]/[PFOA] molar ratio near 1 showed the best UV/Fe³⁺ synergic effect on PFOA defluorination.

Emerging investigator series: contributions of reactive nitrogen species to transformations of organic compounds in water: a critical review

Reactive nitrogen species (RNS) pose a potential risk to drinking water quality because they react with organic compounds to form toxic byproducts. Since the discovery of RNS formation in sunlit surface waters, these reactive intermediates have been detected in numerous sunlit natural waters and engineered water treatment systems. This critical review summarizes what is known regarding RNS, including their formation, contributions to contaminant transformation, and products resulting from RNS reactions. Reaction mechanisms and rate constants have been described for nitrogen dioxide (˙NO₂) reacting with phenolic compounds. However, significant knowledge gaps remain regarding reactions of RNS with other types of organic compounds. Promising methods to quantify RNS concentrations and reaction rates include the use of selective quenchers and probe compounds as well as electron paramagnetic resonance spectroscopy. Additionally, high resolution mass spectrometry methods have enabled the identification of nitr(os)ated byproducts that form via RNS reactions in sunlit surface waters, UV-based treatment systems, treatment systems that employ chemical oxidants such as chlorine and ozone, and certain types of biological treatment processes. Recommendations are provided for future research to increase understanding of RNS reactions and products, and the implications for drinking water toxicity.

Light- and H2O2-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

The redox transformation between the oxidation states of thallium (Tl(I) and Tl(III)) is the key to influencing its toxicity, reactivity, and mobility. Dissolved iron (Fe) is widely distributed in the environment and coexists at a high level with Tl in acidic mine drainages (AMDs). While ultraviolet (UV) light and H₂O₂ can directly (by inducing Tl(III) reduction) and indirectly (by inducing Fe(III) to form reactive intermediates) impact the redox cycles of Tl in Fe(III)-containing solutions, the kinetics and mechanism remain largely unclear. This study is the first to investigate the UV light- and H₂O₂-mediated Tl redox kinetics in acidic Fe(III) solutions. The results demonstrate that UV light and H₂O₂ could directly reduce Tl(III) to Tl(I), with the extent of reduction dependent on the presence of Fe(III) and the solution pH. At pH 3.0, Tl(I) was completely oxidized to Tl(III), which can be ascribed to the generation of hydroxyl radicals (^•OH) from the Fe(III) photoreduction or Fe(III) reaction with H₂O₂. The kinetics of Tl(I) oxidation were strongly affected by the Fe(III) concentration, pH, light source, and water matrix. Kinetic models incorporating Tl redox kinetics with Fe redox kinetics were developed and satisfactorily interpreted Tl(III) reduction and Tl(I) oxidation under the examined conditions. These findings emphasize the roles of the UV light- and H₂O₂-driven Fe cycles in influencing the redox state of Tl, with implications for determining its mobility and fate in the environment.

Efficient removal of PFOA with an In2O3/persulfate system under solar light via the combined process of surface radicals and photogenerated holes

The environmental persistence, high toxicity and wide spread presence of perfluorooctanoic acid (PFOA) in aquatic environment urgently necessitate the development of advanced technologies to eliminate PFOA. Here, the simultaneous application of a heterogeneous In₂O₃ photocatalyst and homogeneous persulfate oxidation (In₂O₃/PS) was demonstrated for PFOA degradation under solar light irradiation. The synergistic effect of direct hole oxidation and in-situ generated radicals, especially surface radicals, was found to contribute significantly to PFOA defluorination. Fourier infrared transform (FTIR) spectroscopy, Raman, electrochemical scanning microscope (SECM) tests and density functional theory (DFT) calculation showed that the pre-adsorption of PFOA and PS onto In₂O₃ surface were dramatically critical steps, which could efficiently facilitate the direct hole oxidation of PFOA, and boost PS activation to yield high surface-confined radicals, thus prompting PFOA degradation. Response surface methodology (RSM) was applied to regulate the operation parameters for PFOA defluorination. Outstanding PFOA decomposition (98.6%) and near-stoichiometric equivalents of fluorides release were achieved within illumination 10 h. An underlying mechanism for PFOA destruction was proposed via a stepwise losing CF₂ unit. The In₂O₃/PS remediation system under solar light provides an economical, sustainable and environmentally friendly approach for complete mineralization of PFOA, displaying a promising potential for treatment of PFOA-containing water.

Reactive Nitrogen Species Generated by Gas-Liquid Dielectric Barrier Discharge for Efficient Degradation of Perfluorooctanoic Acid from Water

Perfluorooctanoic acid (PFOA) poses a serious threat to the ecological environment and biological health because of its ubiquitous distribution, extreme persistence, and high toxicity. In this study, we designed a novel gas-liquid dielectric barrier discharge (GLDBD) reactor which could efficiently destruct PFOA. PFOA removal efficiencies can be obtained in various water matrices, which were higher than 98.0% within 50 min, with energy yields higher than 114.5 mg·kWh^-1. It was confirmed that the reactive species including e^-, ONOOH, •NO₂, and hydroxyl radicals (•OH) were responsible for PFOA removal. Especially, this study first revealed the crucial role of reactive nitrogen species (RNS) for PFOA degradation in the plasma system. Due to the generation of a large amount of RNS, the designed GLDBD reactor proved to be less sensitive to various water matrices, which meant a broader promising practical application. Moreover, influential factors including high concentration of various ions and humic acid (HA), were investigated. The possible PFOA degradation pathways were proposed based on liquid chromatograph-mass spectrometer (LC-MS) results and density functional theory (DFT) calculation, which further confirmed the feasibility of PFOA removal with RNS. This research, therefore, provides an effective and versatile alternative for PFOA removal from various water matrices.

Highly efficient removal of DEET by UV-LED irradiation in the presence of iron-containing coagulant

N,N-Diethyl-3-methyl benzoyl amide (DEET) has been detected as an emerging pollutant in various water bodies because of its widespread use as an insect repellent. In this study, the combination of UV-LED₂₇₅ and iron-containing coagulant (FeCl₃) was used for the elimination of DEET in water. It was found that UV-LED₂₇₅/FeCl₃ (98 %) system presented a favorable removal of DEET compared with UV₂₅₄/FeCl₃ (59 %) and UV-LED₂₇₅/Fe₂(SO₄)₃ (81 %) processes at initial pH 3.5. DEET degradation by both UV-LED₂₇₅/FeCl₃ and UV-LED₂₇₅/Fe₂(SO₄)₃ processes followed pseudo-first-order kinetics with the calculated pseudo-first-order rate constants (k_obs) of 0.0105 and 0.0046 cm² mJ^-1, respectively. The results of ESR analysis and radicals quenching experiments indicated that hydroxyl radicals (OH) and superoxide radicals (O₂^-) were responsible for DEET degradation in UV-LED₂₇₅/FeCl₃ process, and the former played the major role. An increase in FeCl₃ dosage was beneficial to the degradation. In the UV-LED₂₇₅/FeCl₃ process, DEET degradation increased with a decrease in pH from 3.5 to 3.0, whereas it was almost completely suppressed with an increase in pH from 4.3 to 6.3. DEET degradation was almost unchanged after the introduction of NO₃^-, and it impeded after the addition of humic acid (HA), HCO₃^-, and SO₄^2-. The plausible degradation pathway mainly involved hydroxylation, cleavage of the C-N bond, acetylation, and dealkylation. Among the disinfection by-products (DBPs) evaluated, UV-LED₂₇₅/FeCl₃ pretreatment generally increased the generation of trichloromethane, chloral hydrate, dichloroacetic acid, and trichloroacetic acid, which implied that further assessment of environmental risk was needed during its practical applications.

The Roles of Sono-induced Nitrosation and Nitration in the Sono-degradation of Diphenylamine in Water: Mechanisms, Kinetics and Impact Factors

The potential risks of sono-induced nitrosation and nitration side reactions and consequent toxic nitrogenous byproducts were first investigated via sono-degradation of diphenylamine (DPhA) in this study. The kinetic models for overall DPhA degradation and the formation of nitrosation byproduct (N-nitrosodiphenylamine, NDPhA) and nitration byproducts (2-nitro-DPhA and 4-nitro-DPhA) were well established and fitted (R² > 0.98). Nitrosation contributed much more than nitration (namely, 43.3 - 47.3 times) to the sono-degradation of DPhA. The contribution of sono-induced nitrosation ranged from 0.4 to 56.6% at different conditions. The maximum NDPhA formation rate and the contribution of sono-induced nitrosation were obtained at 600 and 200 kHz, respectively, as ultrasonic frequencies at 200 to 800 kHz. Both NDPhA formation rate and the contribution of sono-induced nitrosation increased with increasing power density, while decreased with increasing initial pH and DPhA concentration. PO₄^3-, HCO₃^-, NH₄⁺ and Fe²⁺ presented negative impacts on sono-induced nitrosation in order of HCO₃^- >> Fe²⁺ > PO₄^3- > NH₄⁺, while Br^- exhibited a promoting effect. The mechanism of NDPhA formation via sono-induced nitrosation was first proposed.

Photochemical decomposition of perfluorochemicals in contaminated water

Perfluorochemicals (PFCs) are a set of chemicals containing C-F bonds, which are concerned due to their bioaccumulation property, persistent and toxicological properties. Photocatalytic approaches have been widely studied for the effective removal of PFCs due to the mild operation conditions. This review aims to provide a comprehensive and up-to-date summary on the homogenous and heterogeneous photocatalytic processes for PFCs removal. Specifically, the homogenous photocatalytic methods for remediating PFCs are firstly discussed, including generation of hydrated electrons (e_aq^‒) and its performance and mechanisms for photo-reductive destruction of PFCs, the active species responsible for photo-oxidative degradation of PFCs and the corresponding mechanisms, and metal-ion-mediated (Fe(III) mainly used) processes for the remediation of PFCs. The influences of molecular structures of PFCs and water matrix, such as dissolved oxygen, humic acid, nitrate, chloride on the homogenous photocatalytic degradation of PFCs are also discussed. For heterogeneous photocatalytic processes, various semiconductor photocatalysts used for the decomposition of perfluorooctanoic acid (PFOA) are then discussed in terms of their specific properties benefiting photocatalytic performances. The preparation methods for optimizing the performance of photocatalysts are also overviewed. Moreover, the photo-oxidative and photo-reductive pathways are summarized for remediating PFOA in the presences of different semiconductor photocatalysts, including active species responsible for the degradation. We finally put forward several key perspectives for the photocatalytic removal of PFCs to promote its practical application in PFCs-containing wastewater treatment, including the treatment of PFCs degradation products such as fluoride ion, and the development of noble-metal free photocatalysts that could efficiently remove PFCs under solar light irradiation.

Influence of lattice strain on Fe3O4@carbon catalyst for the destruction of organic dye in polluted water using a combined adsorption and Fenton process

In this study, 8, 25 and 50 wt% Fe3O4@activated carbon (AC) catalysts were prepared by simple coprecipitation method. The efficiency of the catalysts for the advanced Fenton's oxidation process using methylene blue (MB) as a model substrate was tested. Both modified and unmodified activated carbon catalysts exhibited similar activity towards the Fenton's oxidation process. Therefore, it is difficult to identify the role of the catalyst in this dye removal process. Hence, we proposed a new methodology to remove the MB by adopting the adsorption process initially, followed by the Fenton's oxidation process. The proposed process significantly improved the methylene blue decomposition reaction over the 25 wt% Fe3O4@AC catalyst. However, this trend was not seen in pure activated carbon and Fe3O4@AC (8 and 50 wt%) catalysts due to the instability of the material in the oxidizing medium. The possible reason for the deactivation of the catalysts was evaluated from lattice strain calculations, as derived from the modified W-H models (Uniform Deformational Model (UDM), Uniform Stress Deformation Model (USDM) and Uniform Deformation Energy Density Model (UDEDM)). These results provided a quantitative relationship between the experimentally calculated lattice strain values and Fenton's catalytic activity. Furthermore, the optimized strain value and crystalite size of Fe3O4 on the activated carbon matrix are responsible for the high catalytic activity.

The mixotrophic denitrification characteristics of Zoogloea sp. L2 accelerated by the redox mediator of 2-hydroxy-1,4-naphthoquinone

Denitrification in mixed culture system has been extensively researched to date, but few studies have focused on accelerating the process using redox mediators to promote electron transfer. Strain L2, an iron-reducing bacteria, can remove 75.44% of nitrate under temperature of 30.60 °C, pH of 6.75 and Fe²⁺ concentration of 27.86 mg·L^-1. Additionally, the removal rate of nitrate reached 1.516 mg·L^-1·h^-1 in 8 h with the addition of 0.030 mmol·L^-1 2-hydroxy-1,4-naphthoquinone (HNQ), which increased by 1.38 times than control group. Furthermore, analysis by fluorescence spectroscopy, flow cytometer and gas chromatography demonstrated that HNQ positively stimulated denitrification. This study provides a reference for enhancing denitrification in mixed culture and lays the foundation for the practical application of redox mediators in groundwater treatment.