Oxidation of Tris (2-chloroethyl) phosphate in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

A review of the present methods used to remediate soil and water contaminated with organophosphate esters and developmental directions

Organophosphate esters (OPEs) are widely used commercial additives, but their environmental persistence and toxicity raise serious concerns necessitating associated remediation strategies. Although there are various existing technologies for OPE removal, comprehensive screening for them is urgently needed to guide further research. This review provides a comprehensive overview of the techniques used to remove OPEs from soil and water, including their related influencing factors, removal mechanisms/degradation pathways, and practical applications. Based on an analysis of the latest literature, we concluded that (1) methods used to decontaminate OPEs include adsorption, hydrolysis, photolysis, advanced oxidation processes (AOPs), activated sludge processes, and microbial degradation; (2) factors such as the quantity/characteristics of the catalysts/additives, pH value, inorganic ion concentration, and natural organic matter (NOM) affect OPE removal; (3) primary degradation mechanisms involve oxidation induced by reactive oxygen species (ROS) (including •OH and SO4•-) and degradation pathways include hydrolysis, hydroxylation, oxidation, dechlorination, and dealkylation; (5) interference from the pH value, inorganic ion and the presence of NOM may limit complete mineralization during the treatment, impacting practical application of OPE removal techniques. This review provides guidance on existing and potential OPE removal methods, providing a theoretical basis and innovative ideas for developing more efficient and environmentally friendly techniques to treat OPEs in soil and water.

Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

Investigation of the photolysis process of benzo(a)anthracene (BaA) on polyvinyl chloride (PVC) and polystyrene (PS) microplastics: Plastics aging effect, transformation products and toxicity assessment

Microplastics (MPs) and persistent pollutants (POPs) are new pollutants that are extensively studied worldwide. To fill the gaps that the degradation processes and mechanisms of polycyclic aromatic hydrocarbons (PAHs) on the surface of most MPs are still unclear, the photochemical transformation of benzo(a)anthracene (BaA) on polyvinyl chloride (PVC) MPs and polystyrene (PS) MPs in water were investigated and compared. The photolysis of BaA on the surface of PS in water proceeded easier than that on PVC within the 48 h irradiation period, with the pseudo-first-order rate constant of 0.0489 min-1 and 0.0181 min-1, respectively, which can be ascribed to the smaller particle size and more OH production of PS MPs. Due to the light competition between the chromophore and BaA as well as the light-shielding effect, aged MPs showed an inhibitory effect on the degradation of BaA compared with pristine MPs. For BaA/PVC MPs system, the degradation of BaA in real water was not significantly affected by coexisting ions and humic acid (HA) (p < 0.05), while slight inhibitory effect on the degradation of BaA appeared for PS MPs in different water matrices (UP: 86.97 %, YR: 84.47 %, PR: 81.42 % and HR: 83.21 %). According to the electron paramagnetic resonance (EPR) test, quenching experiment and probe experiment, the relative contribution of direct photolysis (PVC: 82.02 %; PS: 69.54 %) and indirect photolysis (PVC: 17.98 %; PS: 30.46 %) was confirmed. A total of 14 products were identified, and the product types were not affected by plastics aging. The results of the toxicity assessment indicated that although some intermediate products remained toxic to aquatic organisms, the toxicity of most products was lower than that of BaA. This study provides new insights into the environmental fate of PAHs and the role of MPs in the photolysis process of contaminants in surface water.

Efficient Discrimination of Hazardous Organophosphate Flame Retardants via Cataluminescence-Based Multidimensional Ratiometric Sensing

Emerging contaminants have recently evolved into a severe worldwide environmental issue. Organophosphate flame retardants (OPFRs) with neurotoxicity, genotoxicity, and reproductive and developmental toxicity are a class of notorious emerging contaminants that cause great concern. The development of high-efficiency and portable sensors for rapid online monitoring of OPFRs has become the primary demand for the exploration of the environmental migration and transformation of OPFRs. In this work, interestingly, the cataluminescence (CTL) phenomenon of OPFRs is first observed, and an ingenious multidimensional ratiometric CTL sensing strategy is developed for the recognition of multiple OPFRs. Three characteristic ratios are extracted from the multipeak CTL spectral curves based on energy transfer of single Tb/Eu-modified MgO sensing material, and thus a novel three-dimensional (3D) code recognition could be mapped out. This obtained 3D coordinate is found to be a unique characteristic for a given OPFR, just like an exclusive person's ID number, which can successfully discriminate and detect 10 kinds of OPFR vapors, including homologous series and isomers. More importantly, CTL mechanism investigations for OPFRs demonstrate that OPFRs undergo a series of chemical reaction processes, e.g., oxidative pyrolysis and hydroxylation, and different high-energy excited intermediates are generated, which trigger discrepant energy-transfer efficiency toward rare earth ions, leading to multipeak spectral profiles. Briefly, this proposed CTL analytical platform for OPFRs recognition initiates a new sensing principle for the efficient identification of emerging contaminants and shows significant prospects on rapid on-site detection.

Critical review on organophosphate esters in water environment: Occurrence, health hazards and removal technologies

Organophosphate esters (OPEs), which are phosphoric acid ester derivatives, are anthropogenic substances that are widely used in commerce. Nevertheless, there is growing public concern about these ubiquitous contaminants, which are frequently detected in contaminated water sources. OPEs are mostly emitted by industrial operations, and the primary routes of human exposure to OPEs include food intake and dermal absorption. Because of their negative effects on both human health and the environment, it is clear that innovative methods are needed to facilitate their eradication. In this study, we present a comprehensive overview of the existing characteristics and origins of OPEs, their possible impacts on human health, and the merits, drawbacks, and future possibilities of contemporary sophisticated remediation methods. Current advanced remediation approaches for OPEs include adsorption, degradation (advanced oxidation, advanced reduction, and redox technology), membrane filtration, and municipal wastewater treatment plants, degradation and adsorption are the most promising removal technologies. Meanwhile, we proposed potential areas for future research (appropriate management approaches, exploring the combination treatment process, economic factors, and potential for secondary pollution). Collectively, this work gives a comprehensive understanding of OPEs, providing useful insights for future research on OPEs pollution.

Thermally activated persulfate (TAP)-enhanced tris(2-chloroethyl) phosphate removal in real-world waters based on a response-surface approach as well as toxicological evaluation on its degradation products

As a typical organophosphorus flame retardant, tris(2-chloroethyl) phosphate (TCEP) is refractory in aqueous environment. The application of TAP is a promising method for removing pollutants. Herein, the removal of TCEP using TAP was rigorously investigated, and the effects of some key variables were optimized by the one-factor-at-a-time approach. To further evaluate the interactions among variables, the response surface methodology (RSM) based on central composite design was employed. Under optimized conditions (pH 5, [PS]0: [TCEP]0 = 500:1), the maximum removal efficiency (RE) of TCEP reached up to 90.6%. In real-world waters, the RE of TCEP spanned the range of 56%- 65% in river water, pond water, lake water and sanitary sewage. The low-concentration Cl- (0.1 mM) promoted TCEP degradation, but the contrary case occurred when the high-concentration Cl-, NO3-, CO32-, HCO3-, HPO42-, H2PO4-, NH4+ and humic acid were present owing to their prominently quenching effects on SO4•-. Both EPR and scavenger experiments revealed that the main radicals in the TAP system were SO4•- and •OH, in which SO4•- played the most crucial role in TCEP degradation. GC-MS/MS analysis disclosed that two degradation products appeared, sourcing from the replacement, oxidation, hydroxylation and water-molecule elimination reactions. The other two products were inferred from the comprehensive literature. As for acute toxicity to fish, daphnid and green algae, product A displayed the slightly higher toxicity, whereas other three products exhibited the declining toxicity as compared to their parent molecule. These findings offer a theoretical/practical reference for high-efficiency removal of TCEP and its ecotoxicological risk evaluation.

Rapid degradation and detoxification of metronidazole using calcium sulfite activated by CoCu two-dimensional layered bimetallic hydroxides: Performance, mechanism, and degradation pathway

In this study, cobalt copper-layered double hydroxides (CoCu-LDHs) were prepared by coprecipitation as catalysts to activate CaSO3 for metronidazole (MNZ) degradation. This is the first report on layered double hydroxides activating sulfite for the degradation of organic pollutants. Meanwhile, to address the issue of self-quenching reactions readily occurring in conventional sulfite advanced oxidation systems and resulting in low oxidant efficiency, CaSO3 with slightly soluble in water was used instead of commonly used Na2SO3, to improve the limitations of traditional systems. The results showed that in the CoCu-LDHs/CaSO3 system, the degradation rate of MNZ reached 98.7% within 5 min, representing a 23.0% increase compared to the CoCu-LDHs/Na2SO3 system. Owing to the excellent catalytic performance exhibited by CoCu-LDHs, characterizations including XRD, FTIR, SEM, TEM, BET and XPS were carried out to investigate this further. The results confirmed the successful synthesis of CoCu-LDH, and the activation mechanism study revealed that Co and Cu were considered to the main elements in activating CaSO3, demonstrating good synergistic effects. In addition, the oxygen vacancies on the catalyst surface also played a positive role in generating radicals and promoting electron transfer. Subsequently, the effects of Co/Cu ratio, catalyst dosage, oxidant concentration, pollutant concentration, pH and coexisting substances on MNZ degradation were investigated. Additionally, based on the LC-MS analysis of degradation products and toxicity tests, MNZ was transformed into different intermediates with low toxicity through four pathways, eventually mineralizing into inorganic small molecules. After six cycles, the MNZ degradation rate still reached 82.1%, exhibiting excellent stability and recyclability. In general, this study provides new ideas for activating sulfite, while providing theoretical support for subsequent research on sulfite advanced oxidation system.

Oxidative degradation and possible interactions of coexisting decabromodiphenyl ether (BDE-209) on polystyrene microplastics in UV/chlorine process

This work was to investigate the transformation of coexisting decabromodiphenyl ether (BDE-209) on microplastics and their possible interactions in UV/chlorine process. Compared with pristine microplastics, the highly aged polystyrene (PS) showed an inhibitory effect on degradation of BDE-209. Increasing initial concentration of BDE-209 on PS inhibited degradation, while the chlorine concentration and pH did not affect the final degradation efficiency. Moreover, the presence of NO3-, SO42-, HCO3- and HA in water was unfavorable for BDE-209 degradation. According to the experimental and calculation results, the contribution to the degradation of BDE-209 was ranked as direct photolysis > HO• > •Cl in the UV/ chlorine system. Chlorination products released by PS during UV/chlorination were detected. Four possible reaction pathways of BDE-209 were proposed, which mainly involved debromination, hydroxylation, chlorine substitution, cleavage of ether bond, and intramolecular elimination of HBr. It was worth noting that PS microplastics not only inhibited the degradation of BDE-209, but also affected the type and abundance of its transformation products. Meanwhile, interaction products of PS and BDE-209 were determined, which was attributed to reactions of PS-derived radicals with •Br/•C6Br5 and •Cl. Results of toxicity evaluation showed that the introduction of carbon-halogen bonds, especially C-Br bond, increased the toxicity of chain scission products of PS. This work provides some new insights into transformation, interaction, and associated ecological risks of coexisting microplastics and surface adsorbed contaminants in the UV/chlorine process of drinking water treatment plants (DWTPs) and wastewater treatment plants (WWTPs).

Experimental and theoretical investigation on degradation of dimethyl trisulfide by ultraviolet/peroxymonosulfate: Reaction mechanism and influencing factors

With a large amount of domestic sewage and industrial wastewater discharged into the water bodies, sulfur-containing organic matter in wastewater produced volatile organic sulfide, such as dimethyl trisulfide (DMTS) through microorganisms, caused the potential danger of drinking water safety and human health. At present, there is still a lack of technology on the removal of DMTS. In this study, the ultraviolet/peroxymonosulfate (UV/PMS) advanced oxidation processes was used to explore the degradation of DMTS. More than 90% of DMTS (30 µg/L) was removed under the conditions of the concentration ratio of DMTS to PMS was 3:40, the temperature (T) was 25 ± 2℃, and 10 min of irradiation by a 200 W mercury lamp (365 nm). The kinetics rate constant k of DMTS reacting with hydroxyl radical (HO·) was determined to be 0.2477 min^-1. Mn²⁺, Cu²⁺ and NO₃^- promoted the degradation of DMTS, whereas humic acid and Cl^- in high concentrations inhibited the degradation process. Gas chromatography-mass spectrometry was used to analyze the degradation products and the degradation intermediates were dimethyl disulfide and methanethiol. Density functional theory was used to predict the possible degradation mechanism according to the frontier orbital theory and the bond breaking mechanism of organic compounds. The results showed that the SS, CS and CH bonds in DMTS molecular structure were prone to fracture in the presence of free radicals, resulting in the formation of alkyl radicals and sulfur-containing radicals, which randomly combined to generate a variety of degradation products.

Activation of peroxymonosulfate for degrading ibuprofen via single atom Cu anchored by carbon skeleton and chlorine atom: The radical and non-radical pathways

Single atomic Cu catalysts (SACs Cu@C) anchored by carbon skeleton and chlorine atom was synthesized by hydrolyzing Cu-MOFs and then pickled by aqua-regia to remove Cu nanoparticles (NPs Cu). Comparative characterizations revealed that SACs Cu@C was a hierarchically porous nanostructure and Cu dispersed uniformly throughout the carbon skeletons. With less active components, SACs Cu@C behaved better in activating PMS over NPs Cu@C on ibuprofen removal (91.3 % versus 30.2 % in 30 min). Two Cu coordination environments were found by EXAF and DFT calculation, including four-coordinated Cu with 4C atoms and six-coordinated Cu with 4Cu and 2Cl atoms. The obvious interfacial electron delivery between PMS and SACs Cu@C was found, which was enhanced by Cl atom. Cu(I)/Cu(II) redox cycle would donate electron to peroxy bond of PMS for generating OH, SO₄^- and O₂^-. But electron transferred in opposite direction when PMS bonded to Cu atom through its terminal oxygen atom in sulfate, which formed ¹O₂. IBP degradation proceeded through both radical and non-radical route. IBP degradation was inhibited with the presence of TBA, methanol and furfuryl alcohol but accelerated by p-BQ, which could accelerate OH generation. Two degradation pathways were deducted. This study provided a new insight into catalysts designed for PMS activation.

Insight into mechanism of peroxydisulfate activation by natural pyrite: Participation of Fe(IV) and regulation of Fe(III)/Fe(II) cycle by sulfur species

In this study, natural pyrite (NP) was used to activate peroxydisulfate (PDS) for imidacloprid (IMD) degradation. NP was characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Effects of key reaction parameters (NP dosage, PDS concentration and initial pH) and co-existing ions on IMD degradation in the NP/PDS system were investigated. Quenching experiments and electron spin resonance (ESR) tests identified the existence of sulfate radical (SO₄^•-), hydroxyl radical (^•OH), singlet oxygen (¹O₂) and superoxide radical (O₂^•-). The cumulative concentration of SO₄^•- and ^•OH were quantified by the formation of benzoquinone (BQ) and p-hydroxybenzoic acid (HBA), respectively. Meanwhile, more than 60% of methylphenyl sulfoxide (PMSO) was selectively converted to methylphenyl sulfone (PMSO₂), revealing that Fe(IV) was dominant in the NP/PDS system. The order of contribution of the three reactive species in the NP/PDS system was Fe(IV) > ^•OH > SO₄^•- (contributions of ¹O₂ and O₂^•- were negligible). Fe(II) released from NP played a crucial role in PDS activation, and sulfur species in NP could also boost Fe(III)/Fe(II) cycle and contribute to the generation of reactive species. Further, the possible degradation pathways of IMD have been proposed based on the detected intermediates using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the toxicity (including acute toxicity, developmental toxicity and mutagenicity) of these intermediates have been predicted using Toxicity Estimation Software Tool (T.E.S.T). Moreover, NP/PDS system was applied in four natural water bodies and IMD degradation efficiency reached more than 97% after adjusting the pH to 3. The fluorescence excitation-emission matrix (EEM) spectra showed that in addition to IMD, NP/PDS system could also remove other impurities.

Influences and mechanisms of phosphate ions onto persulfate activation and organic degradation in water treatment: A review

Currently, various strategies have been applied to activate persulfate (PS) for contaminant removal from water. However, the background phosphate ions in water affect PS activation and organic degradation, and the mechanism of their influence on the processes is still controversial. In this review, the possible effects of different phosphate forms (HPO₄^2-, H₂PO₄^-, and PO₄^3-) on PS activation and contaminant degradation were systematically evaluated and summarized. Specifically, HPO₄^2- promotes contaminant degradation in direct peroxymonosulfate (PMS) oxidation and thermal/PMS systems, while it exhibits inhibition to thermal/peroxodisulfate (PDS) and ultraviolet (UV)/PDS systems. Meanwhile, H₂PO₄^- inhibits most oxidation processes based on PMS and PDS, except for non-metal dominated and metal assisted PMS systems. Coexisting HPO₄^2- and H₂PO₄^- could present beneficial effects in thermal, Co²⁺ and non-metal activated and metal assisted PMS systems. Nevertheless, their inhibitory effects were found in direct PMS oxidation, UV/PMS (or PDS) and metal dominated PMS systems. Generally, phosphate ions inhibit PMS/PDS activation through competing adsorption with PMS or PDS on the solid surface, forming a complex with metal ions, as well as occupying active sites on solid catalysts. In addition, phosphate ions can quench radicals for reduced degradation of contaminants. However, phosphate ions could weaken the bond dissociation energy via combining with PMS and contaminants or form a complex with Co²⁺, thus displaying a facilitative effect. This review further discusses major challenges and opportunities of PS activation with co-existing phosphates and will provide guidance for better PS utilization in real water treatment practice.

A new and systematic review on the efficiency and mechanism of different techniques for OPFRs removal from aqueous environments

Organic phosphorus flame retardants (OPFRs), as a new type of emerging contaminant, have drawn great attention over the last few years, due to their wide distribution in aquatic environments and potential toxicities to humans and living beings. Various treatment methods have been reported to remove OPFRs from water or wastewater. In this review, the performances and mechanisms for OPFRs removal with different methods including adsorption, oxidation, reduction and biological techniques are overviewed and discussed. Each technique possesses its advantage and limitation, which is compared in the paper. The degradation pathways of typical OPFRs pollutants, such as Cl-OPFRs, alkyl OPFRs and aryl OPFRs, are also reviewed and compared. The degradation of those OPFRs depends heavily upon their structures and properties. Furthermore, the implications and future perspectives in such area are discussed. The review may help identify the research priorities for OPFRs remediation and understand the fate of OPFRs during the treatment processes.

Oxidative degradation of sulfamethoxazole from secondary treated effluent by ferrate(VI): kinetics, by-products, degradation pathway and toxicity assessment

Sulfamethoxazole (SMX) is a typical antibiotic in the world, which is frequently detected in the aquatic environment. The current study was aimed to investigate the SMX degradation in secondary treated wastewater using potassium Ferrate [Fe(VI)]. The effects of various experimental conditions, EDTA and phosphate as chelating agents, and toxicity assessment were also considered. Secondary treated effluent was spiked with predefined SMX concentrations, and after desired reaction time with Fe(VI), residual SMX was measured using HPLC. Results indicated that SMX degradation by Fe(VI) was favored under acidic condition, where 90% of SMX degradation was achieved after 120 min. Fe(VI) and SMX reaction obeyed first-order kinetic; meantime, the SMX degradation rate under pH 3 was 7.6 times higher than pH 7. The presence of phosphate (Na₂HPO₄) and EDTA declined SMX degradation, while Fe (III) effect was contradictory. In addition to promising demolition, 10% TOC removal was achieved. Eighteen major intermediates were identified using LC-MS/MS and the degradation pathways were suggested. Transformation products (TPs) were formed due to hydroxylation, bond cleavage, transformation after bond cleavage, and oxidation reactions. The ECOSAR analysis showed that some of the SMX oxidation products were toxic to aquatic organisms (fish, daphnia and green algae).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00769-9.

Flexible construct of N vacancies and hydrophobic sites on g-C3N4 by F doping and their contribution to PFOA degradation in photocatalytic ozonation

N vacancies, hydrophobic sites and electron rich zone were simply regulated by doping F into g-C₃N₄ (CN) to accelerate photocatalytic ozonation of PFOA. Activity of F-CN was superior to that of CN, with 74.3% PFOA removal by F-CN/Vis/O₃ but only 57.1% by CN/Vis/O₃. Experimental results and theory simulations suggested that the photogenerated hole (h_vb⁺) oxidation with the help of N vacancies was vital for PFOA degradation. N vacancies on both CN and F-CN would trap O atom of PFOA and seize electron from α -CF₂ group, which made PFOA more easily to be oxidized. Doping of F narrowed band gap, lowered the valence band position and enhanced the oxidation potential of h_vb⁺. The hydrophobic sites would accelerate the mass transfer of O₃ and PFOA, enhance O₃'s single electron reduction with e_cb^- to generate hydroxyl radicals (•OH) and reduce the recombination of h_vb⁺-e_cb^-. Under the joint function of h_vb⁺, N vacancies and •OH, PFOA degradation in F-CN/Vis/O₃ proceeded through the gradually shortening of perfluoroalky chain and loss of CF₂ unit. The acute and chronic toxicity of generated short-chain perfluorocarboxylic acid toward fish, green algae daphnid were predicted by ECOSAR. And the toxicity change of solutions was examined by luminescent bacteria.

Degradation of tris(2-chloroethyl) phosphate (TCEP) by thermally activated persulfate: Combination of experimental and theoretical study

Organophosphorus esters (OPEs), one kind of the emerging contaminants with high frequency of detection, is rather refractory in natural environment, thus posing great threat to human health. This study investigated the feasibility and mechanism of tris(2-chloroethyl) phosphate (TCEP) degradation in thermally activated persulfate (TAP) system. Influence of impact factors, such as PDS dosage, temperature, initial pH, and presence of natural water matrix (Cl^-, NO₃^-, H₂PO₄^-, NH₄⁺, humic acid), were evaluated. Results showed that 100% degradation of TCEP can be achieved in TAP system in 40 min at 60 °C. SO₄^·- as the dominant oxidant for TCEP degradation was proved by quenching experiment and verified by EPR analysis. Alkaline condition exerted great inhibitory effect by affecting the constituents of oxidative radicals. It is suggested that Cl^- and H₂PO₄^- at lower dosages promoted the degradation by stimulating ·OH production and forming oxidative radicals with better selectivity. Intermediates identified by high resolution mass spectrometer was suggested less toxic than TCEP by ECOSAR program. Meanwhile, the illustrated oxidation mechanism mainly involved radical attack at CCl bond and cleavage of CO bond, as further confirmed by frontier electron density calculation and wavefunction analysis. Moreover, cyclic degradation of TCEP indicated the constant release of SO₄^·- in 450 min, suggesting high efficiency and stability of PDS in TAP system. Four selected OPEs achieved complete removal in TAP system and their degradation discrepancy was further discussed based on the distinctive structures. Altogether, TAP technology can be used as an efficient method in TCEP removal with great potential for application.

Photogenerated aryl mesylate and aryl diethyl phosphate radical cations: a time-resolved spectroscopy investigation

The photoinduced electron transfer reaction of selected aryl sulfonates and phosphates with K2S2O8 in a MeCN water (9 : 1) mixture has been investigated by LFP experiments.

Efficient degradation of minocycline by natural bornite-activated hydrogen peroxide and persulfate: kinetics and mechanisms

Natural bornite (NBo), a sulfide mineral of copper and iron, is one of the main mineral raw materials for copper extraction. In this study, NBo-activated hydrogen peroxide (H₂O₂) and persulfate processes (PS) for the degradation of minocycline (MNC) in aqueous solution were systemically investigated and compared. The MNC removal rates with the NBo/PS and NBo/H₂O₂ processes were 86.40% and 87.50%, respectively. The mineralization rate of NBo/PS (33.96%) was higher than that of NBo/H₂O₂ (29.94%) after reaction for 180 min. The effects of oxidant and activator dosage, pH, common inorganic anions (i.e., Cl^-, NO₃^-, and HCO₃^-), and water composition on MNC degradation were systematically evaluated. In addition, the degradation of MNC in natural water matrix and toxicity evaluation was also studied to better evaluate the feasibility of practical application of those two processes. The results of free radical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) showed that HO· was the main activated species in the NBo/H₂O₂ system, while SO₄^·- and HO· were the main activated species in the NBo/PS system. The degradation of MNC in the NBo/PS system was achieved through electron transfer, while the degradation of MNC in the NBo/H₂O₂ system was mainly achieved through free radical addition. The degradation pathway mainly included deamidation reactions, C-C bond breakage and hydroxylation. Reusability of NBo showed that NBo was considerably stable in activating PS and H₂O₂ for degradation of MNC, which was cost-effective activator. This work provides a new perspective on the degradation mechanism of pollutants by Fe-Cu bimetallic sulfide activation of PS and H₂O₂.

Degradation and chlorination mechanism of fumaric acid based on SO4•-: an experimental and theoretical study

It is well known that chloride ions could affect the oxidation kinetics and mechanism of contaminant based on SO₄^•- in the wastewater. Here, the degradation of an organic acid, fumaric acid (FA), was investigated in the presence of chloride (0-300 mM) by the Fe(II)/peroxymonosulfate (Fe(II)/PMS) system. A negative impact of chloride was observed on the rates of FA degradation. The degree of inhibitory effect was higher in Fe(II)/PMS addition order. Some chlorinated byproducts were identified during the FA oxidation process in the presence of Cl^- by the ultraperformance liquid chromatography and quadrupole-time of flight mass spectrometer (UPLC-QTOF-MS). With the increasing content of Cl^-, an accumulation of adsorbable organic halogen (AOX), an increase in acute toxicity, and an inhibition of mineralization were observed. According to the results of kinetic modeling, the production and transformation of oxidative species were dependent on Cl^- dosage and reaction time. SO₄^•- was supposed to be the main radical for FA degradation with Cl^- concentration below 5 mM, whereas Cl₂^•- was primarily responsible for the depletion of FA at [Cl^-] > 5 mM. A possible degradation pathway of FA was discussed. This study reveals the potential environmental risk of organic acid and is necessary to explore useful strategies for ameliorating the treatment of chloride-rich wastewater.

Effective degradation of 2,4-dihydroxybenzophenone by zero-valent iron powder (Fe0)-activated persulfate in aqueous solution: Kinetic study, product identification and theoretical calculations

2,4-Dihydroxybenzophenone (BP-1), a typically known derivative of the benzophenone-type UV filter, has been frequently detected in aqueous environments and poses a potential risk to human health and the entire ecosystem. In this study, an effective advanced oxidation technique using zero-valent iron powder (Fe⁰)-activated persulfate (PS) was used for the degradation of BP-1. The effects of several experimental parameters, including Fe⁰ dosages, PS dosages, pH, and common natural water constituents, were systematically investigated. The BP-1 degradation efficiency was enhanced by increasing the Fe⁰ and PS dosages and decreasing the solution pH. The presence of different concentrations of humic acid (HA) could inhibit BP-1 removal, while the addition of various cations and anions had different effects on the degradation. Moreover, the degradation of BP-1 in five water matrices was also compared, and the removal rates followed the order of ultrapure water > tap water > secondary clarifier effluent > river water > synthetic water. Thirteen oxidation products were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, and five possible degradation pathways were proposed. The addition reactions initiated by HO and SO₄^-, as well as single-electron coupling reactions and ring-closing reactions, were further supported by density functional theory (DFT) calculations. Assessment of toxicity of intermediates of the oxidation of BP-1 suggested decreased toxicity from the parent contaminant. The present work illustrates that BP-1 could be efficiently degraded in the Fe⁰/PS system, which may provide new insights into the removal of benzophenones in water and wastewater.

Degradation mechanism of tris(2-chloroethyl) phosphate (TCEP) as an emerging contaminant in advanced oxidation processes: A DFT modelling approach

As a typical toxic organophosphate and emerging contaminant, tris(2-chloroethyl) phosphate (TCEP) is resistant to conventional water treatment processes. Studies on advanced oxidation processes (AOPs) to degrade TCEP have received increasing attention, but the detailed mechanism is not yet fully understood. This study investigated the mechanistic details of TCEP degradation promoted by OH by using the density functional theory (DFT) method. Our results demonstrated that in the initial step, energy barriers of the hydrogen abstraction pathways were no more than 7 kcal/mol. Cleavage of the P-O or C-Cl bond was possible to occur, whilst the C-O or C-C cleavage had to overcome an energy barrier above 50 kcal/mol, which was too high for mild experimental conditions. The bond dissociation energy (BDE) combined with the distortion/interaction energy (DIE) analysis disclosed origin of the various reactivities of each site of TCEP. The systematic calculations on the transformation of products generated in the initial step showed remarkable exothermic property. The novel information at molecular level provides insight on how these products are generated and offers valuable theoretical guidance to help develop more effective AOPs to degrade TCEP or other emerging environmental contaminant.

UV-A activation of peroxymonosulfate for the removal of micropollutants from secondary treated wastewater

The occurrence of micropollutants (MPs) in the aquatic environment poses a threat to the environment and to the human health. The application of sulfate radical-based advanced oxidation processes (SR-AOPs) to eliminate these contaminants has attracted attention in recent years. In this work, the simultaneous degradation of 20 multi-class MPs (classified into 5 main categories, namely antibiotics, beta-blockers, other pharmaceuticals, pesticides, and herbicides) was evaluated for the first time in secondary treated wastewater, by activating peroxymonosulfate (PMS) with UV-A radiation, without any pH adjustment or iron addition. The optimal PMS concentration to remove the spiked target MPs (100 μg L^-1) from wastewater was 0.1 mM, leading to an average degradation of 80% after 60 min, with most of the elimination occurring during the first 5 min. Synergies between radiation and the oxidant were demonstrated and quantified, with an average extent of synergy of 69.1%. The optimized treatment was then tested using non-spiked wastewater, in which 12 out of the 20 target contaminants were detected. Among these, 7 were degraded at some extent, varying from 10.7% (acetamiprid) to 94.4% (ofloxacin), the lower removals being attributed to the quite inferior ratio of MPs to natural organic matter. Phytotoxicity tests carried out with the wastewater before and after photo-activated PMS oxidation revealed a decrease in the toxicity and that the plants were able to grow in the presence of the treated water. Therefore, despite the low degradation rates obtained for some MPs, the treatment effectively reduces the toxicity of the matrix, making the water safer for reuse.

Performance of UV/acetylacetone process for saline dye wastewater treatment: Kinetics and mechanism

Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel "halotolerant" chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Cl^- or Br^-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Cl^- or Br^-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r = -d[CV]/dt = k[CV]^a[AA]^b = (7.34 × 10^-4 mM^1-(a+b) min^-1) × [CV]^a=0.16 [AA]^b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (³(AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.

Enhanced electro-Fenton degradation of sulfonamides using the N, S co-doped cathode: Mechanism for H2O2 formation and pollutants decay

Facing low reactivity/selectivity of oxygen reduction reaction (ORR) in electro-Fenton (EF), N, S atoms were introduced into carbon-based cathode. "End-on" O₂ adsorption was achieved by adjusting electronic nature via N doping, while *OOH binding capability was tuned by spin density variation via S doping. Results showed the optimized N, S co-doped cathode presented a 42.47% improvement of H₂O₂ accumulation (7.95 ± 0.02 mg L^-1 cm^-2). According to density functional theory (DFT), N, S co-doped structure favored the "end-on" O₂ adsorption as adsorption energy dropped to - 2.24 eV. Moreover, O-O/C-O bond lengths variation proved a possibility for *OOH desorption. The elaborated cathode was used in EF for sulfonamides (SAs) decay. A 100% removal rate of sulfadiazine (SDZ), sulfathiazole (STZ) and sulfadimethoxine (SDM) was achieved within 60 min, among which SDZ tended to be degraded easily. Because the absolute hardness (η) of those pollutants is ranked as follows: η_SDM> η_STZ> η_SDZ. Degradation pathways were proposed based on the detected byproducts, along with toxicity was evaluated by ecological structure-activity relationship (ECOSAR) program. Results showed that toxic intermediates generated were reduced or even disappeared. EF with N, S co-doped cathode provides a promising process for antibiotics wastewater treatment.

Rapid electrochemical reduction of a typical chlorinated organophosphorus flame retardant on copper foam: degradation kinetics and mechanisms

With the widespread use, chlorinated organophosphorus flame retardants (Cl-OPFRs) as a new emerging contaminant have been widely detected in water environments over the last few years. In this study, the degradation of a typical Cl-OPFR, TCEP (tris (2-chloroethyl) phosphate), by electrochemical reduction was investigated. It was found that copper (Cu) foam as the cathode showed more rapid and effective degradation for TCEP, compared to other cathodes. When TCEP was at the low concentrations (0.1 and 1 mg L^-1), its degradation by Cu foam could reach above 95% within 20 min, and the maximum rate constant was 0.127 min-1. TCEP reduction was little influenced by the co-existing humic substance and anions, except Cl^-. Compared with the reported oxidation methods, electrochemical reduction showed fast and stable degradation for TCEP. For other types of Cl-OPFRs, electrochemical reduction displayed a fast and effective removal for tris (1,3-dichloro-2-propyl) phosphate but lower removal for tris (2-cholroisopropyl) phosphate who possessed methyl units in the branched chains, influencing its reducibility. Based on the product analysis and Fukui function calculation, the bonds of TCEP molecule were found to be gradually broken, and the three oxygen-ethyl-chlorine arms were cleaved one by one. The products including C₆H₁₃Cl₂O₄P (MW = 249.99278 Da), C₄H₉Cl₂O₄P (MW = 221.96105 Da) and C₄H₁₀ClO₄P (MW = 188.0002 Da) were detected at 60 min reaction, and those intermediates showed much lower toxicities than TCEP according to the previous report. The findings may provide a promising treatment for Cl-OPFRs removal from aqueous environments and help understand their reductive fate.

Photodegradation of polychlorinated diphenyl sulfides (PCDPSs) under simulated solar light irradiation: Kinetics, mechanism, and density functional theory calculations

The direct photolysis of 25 individual polychlorinated diphenyl sulfides (PCDPSs) substituted with 1-7 chlorine atoms was investigated using a 500-W Xe lamp. Photolysis of PCDPSs followed pseudo-first-order kinetics, with the higher chlorinated diphenyl sulfides generally degrading faster than the lower chlorinated congeners. A quantitative structure-activity relationship model to predict the photolysis rates of PCDPSs was developed using 16 fundamental quantum chemical descriptors. We found that the substitution pattern for chlorine atoms, the dipole moment, and E_LUMO - E_HOMO were major factors in the photolysis of PCPDSs. The reaction kinetics, products, and photodegradation pathways of 2,2',3',4,5-pentachlorodiphenyl sulfide (PeCDPS) suggest hydroxylation, direct photooxidation, the C-S bond cleavage reaction, and hydroxyl substitution were mainly involved in the photodegradation process, leading to the formation of 13 intermediates, detected by an electrospray time-of-flight mass spectrometer. The initial reaction sites of PCDPSs under photolysis were rationalized by density functional theory calculations. Anions (Cl^-, SO₄^2-, NO₃^-, and HCO₃^-) and Co²⁺ had no influence on the removal of PeCDPS, while Fe³⁺, Cu²⁺, and HA decreased the photolysis efficiency of PeCDPS. This report is the first to develop a logk quantitative structure-property relationships (QSPR) model of 25 PCDPSs and to describe mechanistic pathways for the photolysis of PeCDPS.

Potential environmental toxicity of sewage effluent with pharmaceuticals

Sewage effluent effects on the biochemical parameters of Astyanax bimaculatus organs were investigateted. Treated sewage was collected in a treatment plant; 43 compounds, among them, pharmaceuticals and hormones, were investigated. Caffeine, ciprofloxacin, clindamycin, ofloxacin, oxytetracycline, paracetamol, sulfadiazine, sulfamethoxazole, sulfathiazole and tylosin waste was detected in the collected material. Fish were divided into four groups: control, TSE (treated sewage effluent), TSE + P (TSE with increased concentration of five pharmaceuticals) and PTSE (TSE + P post-treated with O₃/H₂O₂/UV). Biochemical parameters were evaluated in different organs after 14-day exposure. TBARS levels increased significantly in the brain of animals in the TSE and TSE + P groups in comparison to the control. There was significant reduction in TBARS levels recorded for the liver, muscle and gills of animals in the PTSE group in comparison to those of animals in the other groups. AChE activity reduced in the muscle of animals in the groups showing the highest pharmaceutical concentrations. CAT activity in the liver of animals in groups exposed to pharmaceutical effluent was inhibited. GST activity increased in brain of animals in the TSE + P and PTSE groups, whereas reduced levels of this activity were observed in liver of animals in the TSE group. Increased GST activity was observed in the brain of animals in TSE + P and PTSE groups. Based on integrated biomarker response values, the TSE + P group presented greater changes in the analyzed parameters. Results point out that pharmaceutical waste can cause oxidative stress, as well as affect biochemical and enzymatic parameters in Astyanax sp. Post-treatment can also reduce damages caused to fish, even in case of the likely formation of metabolites. Based on these results, these metabolites can be less toxic than the original compounds; however, they were not able to fully degrade the pharmaceutical waste found in the sewage, which can interfere in fish metabolism.

Theoretical Design of Biodegradable Phthalic Acid Ester Derivatives in Marine and Freshwater Environments

The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D‐QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH₂, and DINP−NO₂) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate ^.OH and provides free radicals for the photodegradation of microplastics in the environment.

Tris(2-chloroethyl) phosphate, a pervasive flame retardant: critical perspective on its emissions into the environment and human toxicity

Regulations and the voluntary activities of manufacturers have led to a market shift in the use of flame retardants (FRs). Accordingly, organophosphate ester flame retardants (OPFRs) have emerged as a replacement for polybrominated diphenyl ethers (PBDEs). One of the widely used OPFRs is tris(2-chloroethyl) phosphate (TCEP), the considerable usage of which has reached 1.0 Mt globally. High concentrations of TCEP in indoor dust (∼2.0 × 105 ng g-1), its detection in nearly all foodstuffs (max. concentration of ∼30-300 ng g-1 or ng L-1), human body burden, and toxicological properties as revealed by meta-analysis make TCEP hard to distinguish from traditional FRs, and this situation requires researchers to rethink whether or not TCEP is an appropriate choice as a new FR. However, there are many unresolved issues, which may impede global health agencies in framing stringent regulations and manufacturers considering the meticulous use of TCEP. Therefore, the aim of the present review is to highlight the factors that influence TCEP emissions from its sources, its bioaccessibility, threat of trophic transfer, and toxicogenomics in order to provide better insight into its emergence as an FR. Finally, remediation strategies for dealing with TCEP emissions, and future research directions are addressed.

Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP)

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).

Formation of chloronitrophenols upon sulfate radical-based oxidation of 2-chlorophenol in the presence of nitrite

Sulfate radical (SO₄^-)-based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation technologies widely applied for soil/groundwater remediation. The presence of non-target water constituents may interfere the abatement of contaminants by SR-AOPs as well as result in the formation of unintended byproducts. Herein, we reported the formation of toxic chloronitrophenols during thermally activated persulfate oxidation of 2-chlorophenol (2CP) in the presence of nitrite (NO₂^-). 2-Chloro-4-nitrophenol (2C4NP) and 2-chloro-6-nitrophenol (2C6NP) were identified as nitrated byproducts of 2CP with total yield up to 90%. The formation of nitrated byproducts is a result of coupling reaction between 2CP phenoxyl radical (ClPhO) and nitrogen dioxide radical (NO₂). As a critical step, the formation of ClPhO was supported by density functional theory (DFT) computation. Both 2C4NP and 2C6NP could convert to 2-chloro-4,6-dinitrophenol (2C46DNP) upon further treatment via a denitration-renitration process. The formation rate of 2C4NP and 2C6NP was closely dependent on the concentration of NO₂^-, solution pH, and natural water constituents. ECOSAR calculation suggests that chloronitrophenols are generally more hydrophobic and ecotoxic than 2CP. Our result therefore reveals the potential risks in the abatement of chlorophenols by SR-AOP, particularly when high level of NO₂^- is present in water matrix.

Enhanced removal of tris(2-chloroethyl) phosphate using a resin-based nanocomposite hydrated iron oxide through a Fenton-like process: Capacity evaluation and pathways

The effective removal of organophosphorus compounds (OPs) effectively from water environment remains an important but challenging task. In this study, a resin-based nanocomposite of hydrated iron oxide (HD1) was used as Fenton-like catalyst for effectively catalyzing the decomposition of hydrogen peroxide to degrade tris(2-chloroethyl) phosphate (TCEP). The results showed that HD1 was successfully prepared, which had great versatility, catalytic performance and adsorption capacity. Besides, HD1/H₂O₂ was capable of degrading TCEP completely with less than 0.2 mg/L of inorganic phosphorus (IP) in the effluent at the initial TCEP of 38 mg/L, pH = 4, H₂O₂ dosage of 20 mM, and the K_obs could result in about 1.0530 min^-1 under identical conditions. More attractively, inorganic ions (i.e., Cl-, CO₃²-, SO₄²-, NO₃-, HCO₃-, Ca²⁺, and Mg²⁺) exhibited moderate effect on TCEP degradation. The negative effect of natural organic matters (NOM) (i.e., HA) on the degradation of TCEP was responsible for competition for the active oxygen species. Combined with electron paramagnetic resonance (EPR) spectra, X-ray photoelectron spectroscopy (XPS) and other analytical methods and radical quenching experiments, the possible removal process of TCEP was discussed, including two processes of oxidative degradation and immobilization of IP. Besides, hydroxyl radicals (•OH) was the key active species that contributed to TCEP degradation through hydroxylation-oxidation and C-O bond cracking, and specificity adsorption of HFO on IP was revealed. Furthermore, the results showed that HD1 had desirable acid and alkali resistance. In the continuous running fixed bed column experiment, HD1 showed a satisfactory performance in cycle operations. This work proposed a new enhanced process for removing TCEP in water environment by HD1/H₂O₂, and the multi-functional material, HD1 was promising in treatment of water containing organic phosphorus pollutants. This will be believed that this study will provide new ideas and new materials for the treatment of organic phosphorus-based organic pollutants, and lay the foundation for further deepening and expanding the application of adsorption resins in the field of water pollution control.

Degradation mechanism, intermediates and toxicology assessment of tris-(2-chloroisopropyl) phosphate using ultraviolet activated hydrogen peroxide

Organophosphate flame retardants (OPFRs), one kind of emerging flame retardants, have received prevalent attention owing to their ubiquity in aquatic matrices and their characteristics of being refractory to biodegradation. In current research, the degradation mechanism of tris-(2-chloroisopropyl) phosphate (TCPP), one of OPFRs, and its toxicological evaluation using UV-driven hydroxyl radical oxidation were investigated. A pseudo-first order reaction was fitted with an apparent rate constant (K_obs) of 0.1328 min^-1 on transformation of TCPP in the case of CH₂O₂ 0.1 mM, pH 6.6-7.1 and 4.7 mW cm^-2 UV irradiation. High resolution mass spectroscopy analyses identified nine degradation products (eg., C₆H₁₃Cl₂O₄P (m/z 251.0002), C₉H₁₇Cl₂O₅P (m/z 307.0266), C₉H₁₇Cl₂O₆P (m/z 323.0217), C₉H₁₈Cl₃O₅P (m/z 343.0033)) during transformation of TCPP. The removal efficiency dropped by inhibitory effect of natural organic matters and anions, implying that the complete mineralization of TCPP may be difficult in actual water treatment process. The toxicity assessment has shown an decrease in reactive oxygen species (ROS) and apoptosis, membrane potential (MP) elevation of Escherichia coli, and biological molecular function revision (eg., metabolism and DNA biosynthesis), indicating that toxicity of degradation products were conspicuously decreased in comparison with intact TCPP. To sum up, effective detoxification of TCPP can be realized by a UV driving radical-based oxidation, which will provide an alternative safe treatment method to control TCPP in water matrix.

Oxidation of flumequine in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

The degradation of flumequine (FLU) in aqueous solution by ultraviolet (UV)-activated peroxymonosulfate (PMS) was investigated in this work. Under the conditions of [PMS]₀:[FLU]₀ = 1:1, T = 25 ± 2 °C, pH = 7.0 ± 0.1, nearly complete removal of FLU was achieved after 60 min. The effects of various operating parameters, including oxidant doses, pH, the presence of typical ions (NH₄⁺、Mg²⁺、Fe³⁺、Cl^-、NO₃^-、HCO₃^-) and humic acid were evaluated. It was found that the pseudo-first-order rate constants of FLU degradation increased with increasing PMS dosage and decreasing solution pH. The presence of Mg²⁺ could accelerate FLU removal, while Fe³⁺, HCO₃^-, NO₃^- and HA inhibited the reaction. Moreover, the degradation of FLU in different water matrices were also explored, and the removal followed the order of Tap water > Ultrapure water > River water > Secondary clarifier effluent. According to the control and radical quenching experiment results, direct photolysis and reactive radicals (SO₄^- and HO) contributed mainly to FLU degradation in the UV/PMS system. Initial FLU molecule underwent reactions such as hydroxylation, hydroxyl substitution, demethylation, decarboxylation/decarbonylation and ring opening, leading to the formation of nineteen oxidation products. The effective degradation by UV/PMS suggests a feasible technology for treating FLU in waters and wastewaters.

Enhanced activation of peroxymonosulfte by LaFeO3 perovskite supported on Al2O3 for degradation of organic pollutants

In this study, the effect of various supports on activation of peroxymonosulfate and consequent degradation of Acid Orange 7 (AO7) in aqueous solutions was examined at the presence of LaFeO₃ perovskite as catalyst. Results showed that the AO7 degradation efficiency by LaFeO₃ supported on different supports was in an order of LaFeO₃/Al₂O₃ (86.2%) > LaFeO₃ (70.8%) > LaFeO₃/CeO₂ (59.0%) > LaFeO₃/SiO₂ (52.3%) > LaFeO₃/TiO₂ (32.2%). Moreover, the pseudo first-order rate constant for AO7 degradation by LaFeO₃/Al₂O₃ was 3.2 times than that by LaFeO₃. The enhancement was attributed to its large surface area, abundant chemisorbed surface-active oxygen, redox property and faster electron transfer. AO7 degradation and the leaching of iron ions decreased with the increase of pH. Data of electron spin resonance spectroscopy and quenching experiments revealed that sulfate and hydroxyl radicals were generated on LaFeO₃/Al₂O₃ surface, while sulfate radicals were identified to be the main reactive species responsible for AO7 degradation. Mechanisms for peroxymonosulfate activation were consequently proposed. Furthermore, LaFeO₃/Al₂O₃ catalyst exhibited a superior stability after five cycles. This work provides a new approach for design of iron-based perovskite catalysts with high and stable catalytic activity for removal of organic pollutants from aqueous solutions.

Photochemical formation of hydroxylated polychlorinated biphenyls (OH-PCBs) from decachlorobiphenyl (PCB-209) on solids/air interface

In this work, the photochemical transformation of decachlorobiphenyl (PCB-209) on the surface of several solid particles were systematically evaluated under simulated solar irradiation. The degradation kinetics of PCB-209 were first investigated using silica as a model aerosol particulate. It was found that PCB-209 photodegradation was enhanced at small silica particle size, low surface coverage and low humidity. Electron paramagnetic resonance (EPR) analysis and radicals quenching experiments demonstrated that hydroxyl radicals contributed to PCB-209 degradation. Stepwise hydrodechlorination, hydroxyl addition and cleavage of the CC bridge bond were mainly observed in the reaction process, leading to the formation of lower chlorinated PCBs, hydroxylated PCBs (OH-PCBs) and chlorophenols. Based on density functional theory (DFT) calculation, the dissociation energy of the CCl bond requires 354.81-359.79 kJ/mol energy that corresponds to a wavelength of less than 322 nm. And the minimum activation energy of OH radicals attack on PCB-209 is only 18.12 kJ/mol. Photochemical transformation of PCB-209 can also occur on the surface of natural particles, but the rates were inhibited as compared to silica. The hydroxylation and hydrodechlorination products of PCB-209 were detected in all natural particles. This study would make significant contribution to understanding the fate of PCBs in solids/air interface.

An often-overestimated adverse effect of halides in heat/persulfate-based degradation of wastewater contaminants

Halides (X^-) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO₄^--based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl^- was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br^- are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl^- or PMS/Br^- systems. According to the results of kinetic modeling, SO₄^- was the dominating radical for AO7 degradation without Cl^- or Br^-, but Cl₂^- was the main oxidant in the presence of Cl^-, SO₄^-, Br and Br₂- were responsible for the oxidation of AO7 in the presence of Br^-. The present study assumes that X₂/HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).

Kinetics and model development of iohexol degradation during UV/H2O2 and UV/S2O82- oxidation

The degradation rates and kinetics of one commonly used iodinated contrast medium, iohexol, were investigated and compared during ultraviolet (UV) photolysis, UV/H₂O₂ and UV/S₂O₈^2- advanced oxidation processes (AOPs). Results indicate that the iohexol degradation rate increased in the order of UV/H₂O₂ < UV irradiation < UV/S₂O₈^2- and followed pseudo-first-order kinetics. Increasing persulfate concentration significantly increased iohexol degradation rate, whereas increasing H₂O₂ concentration caused reverse effect. Radical scavenging test results show that UV photolysis, OH and radicals all contributed to iohexol degradation during UV/S₂O₈^2-, but OH was the main contributor during UV/H₂O₂ and was consumed by excess H₂O₂. The kinetic models of iohexol degradation by both AOPs were developed, and the reaction rate constants with OH and were calculated as 5.73 (±0.02) × 10⁸ and 3.91 (±0.01) × 10¹⁰ M^-1 s^-1, respectively. Iohexol degradation rate remained stable at pH 5-9 during UV irradiation and UV/H₂O₂, but gradually decreased at pH 5-7 and remained stable at pH 7-9 during UV/S₂O₈^2-. The presence of anions displayed inhibitory effects on iohexol degradation during UV/S₂O₈^2- in the order of Cl^- >HCO₃^- ≫ SO₄^2-. UV/S₂O₈^2- AOP exhibited high degradation efficiency and stability on the basis of UV irradiation, which can be applied as a promising degradation method for iohexol. UV/S₂O₈^2- AOP can effectively mineralize iohexol to CO₂ but promoted the generation of toxic iodoform (CHI₃), and the subsequent chlorination had the potential to reduce the content of disinfection by-products; therefore, further evaluation of possible environmental hazards is warranted.

Removal of triclosan in a Fenton-like system mediated by graphene oxide: Reaction kinetics and ecotoxicity evaluation

As a typical nanomaterial, graphene oxide (GO) can be easily dispersed in water and may affect the aqueous environment. In this paper, the degradation of triclosan (TCS) in a Fenton-like system Fe³⁺/H₂O₂ in GO aqueous solution was investigated. Interestingly, it was observed that GO at low concentration (2.0 mg/L) could exhibit significant catalytic effect on TCS removal. Meanwhile, results of XPS, Raman and TEM spectroscopy suggested the structure and chemical composition of GO did not exhibit significant change after the oxidation process within 30 min. As per the radical quenching experiments and ESR tests, hydroxyl radical (·OH) was mainly responsible for the decomposition of TCS. Further mechanism study indicated that the reaction activation energy (E_a) could be lowered and the production of ·OH be promoted in the presence of GO, respectively. A total of nine intermediates of TCS degradation were detected by TOF-LC-MS after SPE procedure. Finally, ecotoxicity assessment revealed that degradation of TCS by Fe³⁺/H₂O₂ system in GO aqueous solution could yield by-products of smaller toxicity compared with parent compounds.

Degradation of tris(2-chloroethyl) phosphate (TCEP) in aqueous solution by using pyrite activating persulfate to produce radicals

Organophosphorus esters (OPEs), as one kind of emerging and toxic contaminant are ubiquitous in various environments. This study investigated the degradation of tris(2-chloroethyl) phosphate (TCEP) as a category OPEs by pyrite (FeS₂)-activated persulfate (PS). The result shows that near-100% degradation of TCEP was achieved after 120 min in FeS₂-PS system. The important role of Fe²⁺ in the activation mechanism was confirmed by the introduction of Fe²⁺ into the PS only system. Radical scavengers experiment and electron paramagnetic resonance (EPR) confirmed the presence of SO₄^·- and ·OH，which revealed that ·OH and SO₄^·- played major roles in TCEP degradation. The effect of various environmental factors, including pyrite and oxidant dosage, inorganic ions and pH were investigated. The result indicated that Fe³⁺ and Cl^- can accelerate the degradation rate of TCEP and the reaction between TCEP and FeS₂-PS favors acidic conditions (pH>9). In addition, due to the acidification of pyrite, this system can be applied with a wide pH range. Besides, two oxidation products, C₄H₉Cl₂O₄P and C₂H₆ClO₄P were identified, which suggest that hydroxylation was probably the main mechanism. This study greatly improves our understanding on TCEP removal in FeS₂-PS system.

Enhanced degradation performance of bisphenol M using peroxymonosulfate activated by zero-valent iron in aqueous solution: Kinetic study and product identification

In the present work, we first examined the performance of zero-valent iron (Fe⁰) activated peroxymonosulfate (PMS) for the removal of that bisphenol M (BPM). In 90 min, 95.9 ± 1.0% of BPM (initial concentration of 10 μM) could be removed in the optimal reaction conditions: [BPM]₀:[PMS]₀ = 1:40 (molar ratio), [PMS]₀:[Fe⁰]₀ = 1:3 (molar ratio), pH = 8.0 (maintained by 0.1 M phosphate buffer solution), T = 35 °C. Common environmental ions like HCO₃^-, Cl^-, NO₃^- accelerated BPM degradation while NH₄⁺ hindered it. In radical quenching tests, sulfate radicals (SO₄^-) were found to play a dominant role in BPM degradation, while hydroxyl radicals (OH) were also detected. By high-performance liquid chromatography-tandem mass spectrometry analysis, 13 products of BPM including small molecules, oligomers and hydroxylated derivatives were identified, and five possible degradation pathways were then proposed. The predicted acute toxicity of the reaction products was reduced after BPM was treated by Fe⁰/PMS. All these results prove that Fe⁰/PMS is an efficient, convenient, and environmentally friendly treatment method for the removal of BPM.

Ozonation of pentabromophenol in aqueous basic medium: Kinetics, pathways, mechanism, dimerization and toxicity assessment

Ozonation has been identified effective technique to degrade phenolic compounds, and production of intermediate dimers are major threat. In this study, we systematically investigated the degradation of Pentabromophenol (PBP) in an aqueous medium by using two different ozone generators (sources: air and water). We studied various factors that influenced the degradation kinetics of PBP, including the pH (7.0, 8.0, and 9.0), humic acid (HA) and anions (Cl^-, SO₄^2-, NO₃^-, and HCO₃^-). PBP was efficiently degraded within 5 min (O₃ source: water) and 45 min (O₃ source: air) at pH 8.0 maintained by phosphate buffer. Reaction kinetics revealed 17 b y-products with five possible pathways, including dimers with their isomers and lower bromophenols. Furthermore, the frontier molecular orbital theory was employed to confirm the proposed ozonation pathways, including the breakage of the CO bond at C₅ and C₄ positions, and the cleavage of the CC bond at C₃ and C₆ position. Product P5, P14 (hydroxyl-nonabromophenyl ether) and P15 (dihydroxyl-octabromophenyl ether) were identified with isomers. Ecological Structure Activity Relationships toxicity assessment resulted into the conversion of highly toxic PBP (acute toxicity: LC₅₀ = 0.11 mg L^-1 for fish, LC₅₀ = 0.124 mg L^-1 for daphnia, and EC₅₀ = 0.118 mg L^-1 for green algae) to less harmful products aside from dimers. P14 (acute toxicity: LC₅₀ = 1.04 × 10⁵) found to be more toxic as compare to PBP. From these findings, we concluded that ozonation is an effective and ideal process for PBP degradation.

Formation of perfluorocarboxylic acids from photodegradation of tetrahydroperfluorocarboxylic acids in water

Tetrahydroperfluorocarboxylic acids (2H,2H,3H,3H-PFCAs) have aroused the interest of scholars worldwide due to their potential to generate perfluorinated compounds. In this work, we systematically examined the photodegradation kinetics and mechanisms of typical 2H,2H,3H,3H-PFCAs (C_nF_2n+1C₂H₄COOH, n = 6, 7, 8) in aqueous solution by a 500 W Hg lamp. The photodecomposition of 2H,2H,3H,3H-PFCAs all followed pseudo-first-order kinetics, and the photolysis rate coefficients increased with the increasing carbon chain length. Under the same reaction condition, 2H,2H,3H,3H-PFCAs degraded much faster than the corresponding PFCAs. The photodecomposition rate coefficient of C₈F₁₇CH₂CH₂COOH was accelerated by low pH and Fe³⁺ addition, but decreased by the existence of humic acid, carbonate and bicarbonate. Compared with ultrapure water, a decreased removal of 2H,2H,3H,3H-PFCAs was observed in four types of natural waters, i.e., tap water, Jiuxiang river water, primary effluent and secondary effluent. According to mass analysis, C₈F₁₇CH₂CH₂COOH was mainly decomposed into 8:2 fluorotelomer acid (C₈F₁₇CH₂COOH), shorter-chain perfluorocarboxylic acids (PFCAs), perfluoro-1-enes (C_nF_2n) and perfluoroketenes (C_nF_2n+1CF = C = O). Thus, α-oxidation, decarboxylation and elimination reaction were proposed as reaction pathways. ECOSAR predictions showed that photolysis generally decreased the aquatic toxicity of C₈F₁₇CH₂CH₂COOH.

Naphthalene degradation by Fe2+/Oxone/UV - Applying an unconventional kinetics model and studying the reaction mechanism

This study shows the degradation of naphthalene (Nap) in aqueous solution using Oxone process mediated by Fe²⁺ with UV-A irradiation (FOU). To elucidate the role of different parameters, Fe²⁺/Oxone (FO), Fe²⁺/UV (FU), Oxone/UV (OU) and direct photolysis processes were studied, separately. The degradation efficiency under different dosage of Fe²⁺, Oxone, initial probe compound concentration and solution pH were evaluated. It is concluded that FOU process has significantly better degradation capacity and efficiency. More than 90% of 0.125 mM Nap was removed in 20 min, under the optimal conditions of FOU ([Fe²⁺]₀ = 0.250 mM, [Oxone]₀ = 0.250 mM, wavelength = 350 nm and pH = 2.8). A mathematical model is proposed to describe the two-stage reaction kinetics involving Oxone. To alleviate the problems of radical surge at the initial stage and a radical deficit at later stage, a stepwise addition of oxidants was conducted and achieved a higher removal performance. Besides, the decay pathways of Nap under FOU process were proposed by using LC-ESI/MS analysis. The TOC content was found to be increased initially and decreased after 2 h reaction. It is clarified that the TOC increment was contributed by the partially degraded intermediates rather than the persistent Nap, since the latter was not completely combustible in the TOC analyzer, demonstrating that the FOU process is effective in degrading Nap into more degradable products such naphthoic acids and aldehydes.