Benzoquinone-assisted heterogeneous activation of PMS on Fe3S4 via formation of active complexes to mediate electron transfer towards enhanced bisphenol A degradation

Layered clay confined single-atom catalyst for enhanced radical pathway to achieve ultrafast degradation of bisphenol A

Seeking a technically promising method and cost-effective material to synthesize carrier-supported single-atom catalysts has attracted on-going research interests to overcome the low productivity and high costs for their industrial application. Montmorillonite (MT), a natural silicate clay mineral, has specific two-dimensional layered structure, and could be an excellent carrier, which creates a unique microenvironment to enhance molecule adsorption and interfacial reactions within the single atoms, free radicals and pollutants in the heterogeneous catalytic system. We synthesized cobalt single-atom catalyst (Co-SAC) by ball milling MT and cobalt salt using surface and spatial confinement strategy. Co-SAC/MT catalyst was used to activate peroxymonosulfate for degrading emerging contaminants bisphenol A (BPA). Characterization results revealed that Co single atoms were confined in the interlayer of MT as Co-O6-Si. Co-SAC/MT catalyst demonstrated remarkable molecular interaction capabilities to shorten mass transfer distance of free radical diffusion to the target pollutants, enhance the utilization rate of free radicals, and thus improve the efficiency of oxidation reaction. The BPA solution was completely degraded in 3 min, with a mineralization rate of 75.7 % in 10 min. This study provides a simple and efficient method for the preparation of single-atom catalysts, which is expected to achieve large-scale production of single-atom catalysts.

Differential catalytic mechanism induced by selective adsorption of pollutants in metal clusters decorated single atom catalyst mediated heterogeneous Fenton-like reaction

Although metal clusters are generally considered as impurities accompanying the synthesis of single atom catalysts, their extraordinary potential in regulating single atom catalytic reactions has attracted widespread attention. In this study, iron cluster decorated single atom iron catalyst (Fe-SACAs) were synthesized to activate peroxymonosulfate (PMS) for the removal of organic pollutants, and a differential PMS activation mechanism induced by selective adsorption of pollutants was observed for the first time. The chemical coordination between pollutants and active sites was identified as the dominant chemisorption mechanism for the adsorption of organic pollutants by Fe-SACAs. The competitive occupation of PMS activation sites by pollutants induced by the diversity of targeted pollutant molecules in ionization potentials was thereby revealed to be the inducement for the adsorption-dependent oxidation. The adsorption-dependent oxidation mechanism was fully elucidated using density functional theory (DFT). Finally, an optimized treatment process was proposed based on the adsorption-dependent oxidation mechanism, which achieved zero oxidant residue and pollutant emission simultaneously. This study unveils the crucial effect of reactant mass transfer and adsorption on the oxidation process in Fe-SACAs mediated Fenton-like reactions.

Fluoride ions enhanced cobalt ferrite for peroxymonosulfate activation with efficient performance and active oxygen yield regulation

The activation of peroxymonosulfate (PMS) by cobalt-based catalysts for the degradation of organic pollutants has been widely studied, while the role of coexisting anions has received little attention. In this study, the performance of atrazine (ATZ) degradation by the addition of fluoride ions (F-) in the activation of PMS by cobalt ferrite (CoFe2O4) was investigated. The addition of F- to the CoFe2O4/PMS system increased ATZ degradation effect from 82 % to 98 % within 10 min, and the rate increased from 0.172 min-1 to 0.431 min-1. At the same time, F- could also enhance the degradation of organic substances such as sulfamethoxazole (SMX), ibuprofen, and iohexol. Based on generating SO4•-, HO• and Co(IV)=O in the CoFe2O4/PMS system, F- enhanced the generation of SO4•-. When coexisting with common substances in water (i.e., inorganic anions, humic acid, hemoglobin and dextran), F- can still increase the reaction rate and reduce their negative impacts. Ion dissolution and control tests verified Co as a valid active site. A potential reaction mechanism was proposed for the complex Co(II)F formation with Co by F-, which enhanced the activation of the PMS by CoFe2O4 and regulated the active species. Finally, it was verified that the low concentration of F- could enhance ATZ degradation within two hours and the remaining F- could be effectively removed by flocculation and precipitation. This research takes utilization of F- in wastewater to promote advanced oxidation processes based on PMS, which provides a new direction for the treatment of actual water pollution.

Enhanced Fe(III)/Fe(II) Cycle by Lattice Sulfur for Continuous Fenton Reactions

The Fenton reaction is usually limited by the sluggish regeneration of Fe(II). In this article, we developed a Fenton system that uses metal sulfides (MSx) and diluted Fe(III) to activate H2O2, and the enhanced mechanism of the Fe(III)/Fe(II) cycle in the presence of sulfides was investigated. The lattice sulfur of MSx can donate electrons to reduce Fe(III) into Fe(II) and is partially oxidized to SO42- during H2O2 activation. •OH and 1O2 are the primary reactive oxygen species for pollutant removal. Meanwhile, low-cost iron-based sulfide (FeSx) is selected for scale-up experiments in a fixed-bed reactor, which can maintain 100% atrazine degradation over 240 h. Additionally, the Fukui function is employed to analyze the selective degradation pathway of atrazine, and the biological toxicity of the organic intermediates is also assessed. The novel FeSx/Fe(III) system provides a potential alternative to the traditional Fenton reaction.

Exploring the degradation of ofloxacin in sewer overflows by Fe(Ⅵ)/PMS, Fe(Ⅵ)/PDS, and Fe(Ⅵ)/SPC: Overlooked synergistic effect of oxidation and in-situ coagulation

Sewer overflows are a potential source of emerging contaminants to urban waters, posing a threat to ecosystems and human health. Herein, the performance and mechanism of ferrate(Ⅵ) (Fe(Ⅵ))/peroxymonosulfate (PMS), Fe(Ⅵ)/peroxydisulfate (PDS), and Fe(Ⅵ)/percarbonate (SPC) for the degradation of ofloxacin (OFL) in overflows were comparatively investigated. These systems achieved efficient degradation of OFL and the removal of conventional pollutants. Particularly, Fe(Ⅵ)/PMS showed better degradation performance for OFL with a degradation efficiency of 98.8 %. The dominant reactive oxygen species for OFL degradation in the Fe(Ⅵ)/PMS, Fe(Ⅵ)/PDS, Fe(Ⅵ)/SPC systems were singlet oxygen (1O2), sulfate radical (SO4·-), and hydroxyl radical (·OH), respectively. High-valent iron species played an important role in the Fe(Ⅵ)/PMS and Fe(Ⅵ)/PDS systems. Notably, the synergistic effect of oxidation and in-situ coagulation played a key role in OFL degradation, which determined the superior performance of Fe(Ⅵ)/PMS. The formed flocs with Fe-O-P bond acted as a highway to promote the electron transfer from OFL to PMS, resulting in the efficient degradation of OFL in Fe(Ⅵ)/PMS system. Moreover, a same degradation pathway of OFL was found, and the toxicity of the degradation products was reduced, especially in the Fe(Ⅵ)/PMS system. This study provided a new strategy for overflows treatment.

Recent Progress in Molecular Oxygen Activation by Iron-Based Materials: Prospects for Nano-Enabled In Situ Remediation of Organic-Contaminated Sites

In situ chemical oxidation (ISCO) is commonly used for the remediation of contaminated sites, and molecular oxygen (O2) after activation by aquifer constituents and artificial remediation agents has displayed potential for efficient and selective removal of soil and groundwater contaminants via ISCO. In particular, Fe-based materials are actively investigated for O2 activation due to their prominent catalytic performance, wide availability, and environmental compatibility. This review provides a timely overview on O2 activation by Fe-based materials (including zero-valent iron-based materials, iron sulfides, iron (oxyhydr)oxides, and Fe-containing clay minerals) for degradation of organic pollutants. The mechanisms of O2 activation are systematically summarized, including the electron transfer pathways, reactive oxygen species formation, and the transformation of the materials during O2 activation, highlighting the effects of the coordination state of Fe atoms on the capability of the materials to activate O2. In addition, the key factors influencing the O2 activation process are analyzed, particularly the effects of organic ligands. This review deepens our understanding of the mechanisms of O2 activation by Fe-based materials and provides further insights into the application of this process for in situ remediation of organic-contaminated sites.

The Dual Role of Natural Organic Matter in the Degradation of Organic Pollutants by Persulfate-Based Advanced Oxidation Processes: A Mini-Review

Persulfate-based advanced oxidation processes (PS-AOPs) are widely used to degrade significant amounts of organic pollutants (OPs) in water and soil matrices. The effectiveness of these processes is influenced by the presence of natural organic matter (NOM), which is ubiquitous in the environment. However, the mechanisms by which NOM affects the degradation of OPs in PS-AOPs remain poorly documented. This review systematically summarizes the dual effects of NOM in PS-AOPs, including inhibitory and promotional effects. It encompasses the entire process, detailing the interaction between PS and its activators, the fate of reactive oxygen species (ROS), and the transformation of OPs within PS-AOPs. Specifically, the inhibiting mechanisms include the prevention of PS activation, suppression of ROS fate, and conversion of intermediates to their parent compounds. In contrast, the promoting effects involve the enhancement of catalytic effectiveness, contributions to ROS generation, and improved interactions between NOM and OPs. Finally, further studies are required to elucidate the reaction mechanisms of NOM in PS-AOPs and explore the practical applications of PS-AOPs using actual NOM rather than model compounds.

Efficiently photocatalysis activation of peroxymonosulfate by bimetallic metal-organic frameworks Mn-MIL-53(Fe) for ibuprofen degradation: Synergistic efficiency, mechanism and degradation pathways

In this study, a UV-driven photocatalytic activation of peroxymonosulfate (PMS) system was constructed using bimetallic metal-organic frameworks to degrade pharmaceuticals and personal care products (PPCPs). Mn-MIL-53(Fe) was successfully synthesised by adjusting the doping ratio of Mn using solvothermal method. The removal of ibuprofen (IBP) by UV/Mn-MIL-53(Fe)/PMS process was as high as 79.7% in 30 min with a Mn doping ratio of 1.0 (molar ratio of Mn to Fe), and the reaction rate constant was 26.9% higher than undoped. Mn-MIL-53(Fe) had been systematically characterized in terms of its physical structure, microscopic morphology, surface functional groups and photoelectric properties. The mechanism investigation revealed that the cycling of Mn and Fe accelerated the rate of electron transfer in the system, which significantly increased the activation efficacy of PMS to generate more hydroxyl and sulfate radicals for IBP degradation. A total of 13 transformation products were detected during the degradation of IBP by the UV/Mn-MIL-53(Fe)/PMS process. Theoretical calculations were used to predict the sites on the IBP molecule that were vulnerable to attack, and four possible degradation pathways were deduced. The excellent stability and efficient catalytic properties of Mn-MIL-53(Fe) provided a promising solution to the problem of water treatment contaminated with PPCPs.

FePO4/WB as an efficient heterogeneous Fenton-like catalyst for rapid removal of neonicotinoid insecticides: ROS quantification, mechanistic insights and degradation pathways

Iron-based catalysts for peroxymonosulfate (PMS) activation hold considerable potential in water treatment. However, the slow conversion of Fe(III) to Fe(II) restricts its large-scale application. Herein, an iron phosphate tungsten boride composite (FePO4/WB) was synthesized by a simple hydrothermal method to facilitate the Fe(III)/Fe(II) redox cycle and realize the efficient degradation of neonicotinoid insecticides (NEOs). Based on electron paramagnetic resonance (EPR) characterization, scavenging experiments, chemical probe approaches, and quantitative tests, both radicals (HO• and SO4⋅-) and non-radicals (1O2 and Fe(IV)) were produced in the FePO4/WB-PMS system, with relative contributions of 3.02 %, 3.58 %, 6.24 %, and 87.16 % to the degradation of imidacloprid (IMI), respectively. Mechanistic studies revealed that tungsten boride (WB) promoted the reduction of FePO4, and the generated Fe(II) dominantly activated PMS through a two-electron transfer to form Fe(IV), while a minority of Fe(II) engaged in a one-electron transfer with PMS to produce SO4⋅-, HO•, and 1O2. In addition, four degradation pathways of NEOs were proposed by analyzing the byproducts using UPLC-Q-TOF-MS/MS. Besides, seed germination experiments revealed the biotoxicity of NEOs was significantly reduced after degradation via the FePO4/WB-PMS system. Meanwhile, the recycling experiments and continuous flow reactor experiments showed that FePO4/WB exhibited high stability. Overall, this study provided a new perspective on water remediation by Fenton-like reaction. ENVIRONMENTAL IMPLICATION: Neonicotinoids (NEOs) are a type of insecticide used widely around the world. They've been found in many aquatic environments, raising concerns about their possible negative effects on the environment and health. Iron-based catalysts for peroxymonosulfate (PMS) activation hold great promise for water purification. However, the slow conversion of Fe(III) to Fe(II) restricts its large-scale application. Herein, iron phosphate tungsten boride composite (FePO4/WB) was synthesized by a simple hydrothermal method to facilitate the Fe(III)/Fe(II) redox cycle and realize the efficient degradation of NEOs. The excellent stability and reusability provided a great prospect for water remediation.

Highly efficient targeted adsorption and catalytic degradation of ciprofloxacin by a novel molecularly imprinted bimetallic MOFs catalyst for persulfate activation

Given the presence of emerging pollutants at low concentrations in water bodies, which are inevitably affected by background substances during the removal process. In this study, we synthesized molecularly imprinted catalysts (Cu/Ni-MOFs@MIP) based on bimetallic metal-organic frameworks for the targeted degradation of ciprofloxacin (CIP) in advanced oxidation processes (AOPs). The electrostatic interaction and functional group binding of CIP with specific recognition sites on Cu/Ni-MOFs@MIP produced excellent selective recognition (Qmax was 14.82 mg g-1), which enabled the active radicals to approach and remove the contaminants faster. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed the coexistence of ∙OH, SO42-, and 1O2, with ∙OH dominating the system. Based on experimental and theoretical calculations, the reaction sites of CIP were predicted and the possible degradation pathways and mechanisms of Cu/Ni-MOFs@MIP/PMS systems were proposed. This study opens up a new platform for the targeted removal of target pollutants in AOPs.

Selective and ultrafast oxidation of multiple pollutants by biomorphic diatomite-based catalyst and stable catalytic Fenton-like membrane: Degradation behavior and mechanism analysis

Carbon-driven advanced oxidations show great potential in water purification, but regulating structures and properties of carbon-based catalysts to achieve ultrafast Fenton-like reactions remains challenging. Herein, a biomorphic diatomite-based catalyst (BD-C) with Si-O doping was prepared using natural diatomite as silicon source and porous template. The results showed that the metal-free BD-C catalyst exhibited ultrafast oxidation performances (0.95-2.58 min-1) towards a variety of pollutants in PMS-based Fenton-like reaction, with the Fenton-like activity of metal-free catalyst comparable to metal-based catalysts or even single-atom catalysts. Pollutants (e.g., CP, BPA, TC, and PCM) with electron-donating groups exhibited extremely low PMS decomposition with overwhelmed electron transfer process (ETP), while high PMS consumption was induced by the addition of electron-withdrawing pollutants (e.g., MNZ and ATZ), which was dominated by radical oxidation. The BD-C/PMS system also showed a high ability to resist the environmental interference. In-depth theoretical investigations demonstrated that the coordination of Si-O can lower the potential barrier of PMS activation for accelerating the generation of radicals, and also promote the electron transfer from pollutants to the BD-C/PMS complexes. In addition, BD-C was deposited onto a polytetrafluoroethylene membrane (PTFEM) with 100% of pollutants removal over 10 h, thereby revealing the promising prospects of utilizing BD-C for practical applications.

Facile synthesis of pyrite FeS2 on carbon spheres for high-efficiency Fenton-like reaction

Designing iron-based catalysts for Fenton-like reactions with peroxymonosulfate (PMS) as oxidants have attracted growing attentions. Herein, pyrite FeS2 supported on carbon spheres (FeS2@C) is synthesized by a facile low-temperature method. The FeS2@C/PMS system can degrade carbamazepine (CBZ) effectively in a wide pH range. Sulfate radicals (SO4·-), hydroxyl radicals (·OH), superoxide radical (O2·-), and singlet oxygen (1O2) are the responsible reactive oxygen species (ROSs) for CBZ degradation. Moreover, in the simulated fixed-bed reactor, the FeS2@C/PMS system can maintain a high CBZ removal ratio of >95% for than 8 h, exhibiting its excellent stability. The outstanding performance of FeS2@C/PMS system is attributed to the presence of carbon spheres and lattice S2-, which together promote the Fe(III)/Fe(II) redox cycle. The FeS2@C is a promising catalyst due to its facile synthesis, low cost, high efficiency, and excellent stability to activate PMS for organics degradation.

Exposed {110} facets of BiOBr anchored to marigold-like MnCo2O4 with abundant interfacial electron transfer bridges and efficient activation of peroxymonosulfate

Precise charge transfer modification and efficient activation of peroxymonosulfate are effective methods for increasing photocatalytic efficiency. Here, BiOBr/MnCo2O4 photocatalysts with abundant Mn-Br bonds were generated by immobilizing the exposed {110} facets of BiOBr in the marigold-like MnCo2O4. The prepared BiOBr/MnCo2O4 retained the marigold-like morphology of MnCo2O4 while exhibiting good adsorption properties and interface contact effects. More importantly, the interfacial Mn-Br bond between MnCo2O4 and BiOBr functioned as charge transport bridges, allowing for a directional transfer channel and lowering the potential energy barrier for interfacial charge transfer. In addition, the exposure of the {110} facets exhibited more Mn atom-anchored sites for easy anchoring of BiOBr, significantly solving the stability problem of the bismuth material. Compared to MnCo2O4 + BiOBr, which did not form Mn-Br bonds, the MnCo2O4/BiOBr heterojunction had more efficient photocatalytic activity (1.3 times) and stability. This suggested that using electronic bridges for directional charge transfer was an efficient way to improve photocatalytic efficiency.

Tailored short-chain fatty acids conversion from waste activated sludge fermentation via persulfate oxidation and C3-C5 io-SRB metabolizers

Boosting acetate production from waste activated sludge (WAS) fermentation is often hindered by the inefficient solubilization in the hydrolysis step and the high hydrogen pressure ( [Formula: see text] ) during the acidogenesis of C3-C5 short-chain fatty acid (SCFAs), i.e., propionate (HPr), butyrate (HBu) and valerate (HVa). Therefore, this study employed persulfate (PS) oxidation and C3-C5 incomplete-oxidative sulfate reducing bacteria (io-SRB) metabolizers to tailor SCFAs conversion from WAS fermentation. The decomposition efficiency, performance of SCFAs production was investigated. Results showed that the PS significantly promoted WAS decomposition, with a dissolution rate of 39.4%, which is 26.0% higher than the un-treated test. Furthermore, SCFAs yields were increased to 462.7 ± 42 mg COD/g VSS in PS-HBu-SRB, which was 7.4 and 2.2 times higher than that of un-treated and sole PS tests, respectively. In particular, the sum of acetate and HPr reached the peak value of 85%, indicating that HBu-SRB mediation promoted the biotransformation of HBu and macromolecular organics by reducing the [Formula: see text] restriction. Meanwhile, sulfate radical (SO4∙-)-based oxidation (SR-AOPs) was effective in the decomposition of WAS, the oxidative product, i.e., sulfate served the necessary electron acceptor for the metabolism of io-SRB. Further analysis of Mantel test revealed the cluster of the functional genus and their interaction with environmental variables. Additionally, molecular ecological network analysis explored the potential synergistic and competitive relationships between critical genera. Additionally, the potential synergistic and competitive relationships between critical genera was explored by molecular ecological network analysis. This study provides new insights into the integration of SR-AOPs with microbial mediation in accelerating SCFAs production from WAS fermentation.

Effective degradation of 2,4,4'-trichlorodiphenyl by Fe3C@Fe-800 activated peroxymonosulfate: Superoxide radical and singlet oxygen-dominated advanced oxidation process

Polychlorinated biphenyls (PCBs) degradation by peroxymonosulfate (PMS) activation through •OH and SO₄^•- radical oxidation process was the effective technology in the last decades; however, there were few research focusing on removing PCBs by O₂^•- and ¹O₂ induced by PMS activation. In this work, 90.86% of 2,4,4-trichlorodiphenyl (PCB 28) was degraded by 0.3 g/L Fe₃C@Fe-800 activated 0.5 mM PMS system under the synergistic action of O₂^•- and ¹O₂. The structures of Fe₃C@Fe-800 were identified by Scanning electron microscope (SEM), High resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), Raman spectra and Fourier transform infrared (FT-IR) spectra. Electron paramagnetic resonance (EPR) measurements and quenching tests verified that O₂^•- and ¹O₂ were the primary reactive species in Fe₃C@Fe-800/PMS/PCB 28 ternary reaction system. Density functional theory (DFT), Linear sweep voltammetry (LSV), and chronoamperometry test revealed that electron-deficient Fe atoms on Fe₃C were the main active sites in Fe₃C@Fe-800 for PMS activation to generate ¹O₂. Unlike the reported •OH and SO₄^•- mediated degradation induced by the iron-based catalyst, both O₂^•- and ¹O₂ contributed to PCB 28 degradation： nucleophilic dichlorination reaction by O₂^•- and then ring-open oxidation process by ¹O₂. Fe₃C@Fe-800/PMS system had excellent catalytic performance under different reaction conditions and possessed desirable inorganic salt and natural organic matter resistance. This work elucidated the important role of Fe₃C in PMS activation to generate O₂^•- and ¹O₂ for PCB 28 decontamination by nonradical way and provided a clue to design rationally catalysts in polychlorinated biphenyl pollution remediation.