Peroxymonosulfate activation by different iron sulfides for bisphenol-A degradation: Performance and mechanism

Revealing the vital role of sulfur site on the surface of pyrite in 1O2 formation for promoting ciprofloxacin degradation via peracetic acid activation

Pyrite has been widely utilized to activate oxidants for water treatment, yet the regulation of reactive oxygen species (ROS) by sulfur sites on its surface has been overlooked. In this study, the surface sulfur sites were regulated by thermal modification of natural pyrite in the N2 atmosphere (denoted as P-X, where X represented pyrolysis temperatures ranging from 400 to 700 °C), and these modified pyrites were employed to activate peracetic acid (PAA) for ciprofloxacin (CIP) degradation. The results revealed that the degradation rate of CIP increased as the reduced sulfur content increased, with the P600/PAA system achieving the highest apparent degradation rate (kobs = 0.0999 min-1). Quenching experiments and electron paramagnetic resonance (EPR) analysis identified various ROS involved in the P-X/PAA system, with hydroxyl radical (·OH) and singlet oxygen (1O2) identified as dominant reactive species responsible for CIP degradation. The reduced sulfur sites served as the primary active sites facilitating the conversion of organic radicals (·CH3C(O)OO) into superoxide radicals (·O2-) and 1O2. Furthermore, the P600/PAA system demonstrated robust adaptability under both acidic and neutral pH conditions, efficiently degrading CIP even in the presence of complex matrices such as Cl-, NO3-, SO42-, NH4+, or humic acid (HA) in water bodies, although HCO3- was found to inhibit CIP degradation. This study significantly enhances our understanding of the interaction between reduced sulfur sites and ROS in PAA-based advanced oxidation processes (AOPs), offering a promising technology for efficient antibiotic treatment in water purification.

Tungsten sulfide highly boosted Fe(III)/peroxymonosulfate system for rapid degradation of cyclohexanecarboxylic acid: Performance, mechanisms, and applications

In this study, the Fe(III)/WS2/peroxymonosulfate (PMS) system was found to remove up to 97% of cyclohexanecarboxylic acid (CHA) within 10 min. CHA is a model compound for naphthenic acids (NAs), which are prevalent in petroleum industrial wastewater. The addition of WS2 effectively activated the Fe(III)/PMS system, significantly enhancing its ability to produce reactive oxidative species (ROS) for the oxidation of CHA. Further experimental results and characterization analyses demonstrated that the metallic element W(IV) in WS2 could provide electrons for the direct reduction of Fe(III) to Fe(II), thus rapidly activating PMS and initiating a chain redox process to produce ROS (SO4•-, •OH, and 1O2). Repeated tests and practical exploratory experiments indicated that WS2 exhibited excellent catalytic performance, reusability and anti-interference capacity, achieving efficient degradation of commercial NAs mixtures. Therefore, applying WS2 to catalyze the Fe(III)/PMS system can overcome speed limitations and facilitate simple, economical engineering applications.

FeSe2 and Its Composites for Pollutants Removal: Synthesis, Mechanisms, and Application Potential

In recent years, the research of FeSe2 and its composites in environmental remediation has been gradually carried out. And the FeSe2 materials show great catalytic performance in photocatalysis, electrocatalysis, and Fenton-like reactions for pollutants removal. Therefore, the studies and applications of FeSe2 materials are reviewed in this work, including the common synthesis methods, the role of Fe and Se species as well as the catalyst structure, and the potential for practical environmental applications. Hereinto, it is worth noting in particular that the lower-valent Se (Se2-), unsaturated Se (Se-), and Se vacancies (VSe) can play different roles in promoting pollutants removal. In addition, the FeSe2 material also demonstrates high stability, reusability, and adaptability over a wider pH range as well as universality to different pollutants. In view of the overall great properties and performance of FeSe2 materials compared with other typical Fe-based materials, it deserves and needs further research. And finally, this paper presents some challenges and perspectives in future development, looking forward to providing helpful guidance for the subsequent research of FeSe2 and its composites for environmental application.

Construction of phase-separated Co/MnO synergistic catalysts and integration onto sponge for rapid removal of multiple contaminants

Wastewater treatment recycling is critical to ensure safe water supply or to overcome water shortage. Herein, we developed metallic Co integration onto MnO nanorods (MON) resulting in a phase-separated synergetic catalyst by creating more Mn(III) via the Jahn-Teller effect and oxygen vacancies and improving the redox capability of Co nanoparticles mediated by a thin carbon layer. Additionally, the N-doped surface carbon network on MON contributes to polar sites, facilitating the enrichment of contaminants around reactive sites, thereby shortening the migration of reactive oxidative species (ROS) toward contaminants. The optimized MnO@Co/C-600 exhibits superior PMS activation efficiency for bisphenol A degradation (0.463 min-1), displaying nearly a 20-fold enhancement in the rate constant compared to Mn3O4/C-600. Subsequent experiments involving variable modulation and extension were conducted to further elucidate the multiple synergistic effects. The mechanism study further confirms the synergy of ˙SO4-, ˙OH, ˙O2-, and 1O2, along with additional electron transfer pathways. The intermediates generated during degradation pathways and their toxicity to aquatic organisms were identified. Notably, a monolith integrated catalyst was explored by anchoring MnO@Co/C-600 onto a tailored melamine sponge based on Ca ion triggered crosslink tactic for the photothermal degradation of bisphenol A, tetracycline and norfloxacin, endowed with easy recovery and good stability. Furthermore, we demonstrated that the total organic carbon removal of multiple contaminants surpassed that of sole contaminants.

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.

FeS and Fe3O4 Co-modified biochar to build a highly resistant advanced oxidation process system for quinclorac degradation in irrigation water

Advanced oxidation processes (AOPs), based on sulfate radical (SO4·-) produced by peroxymonosulfate (PMS), can effectively mineralize refractory organic pollutants. However, the coexistence of anions and natural organic matters in actual wastewater prevents the application of AOPs. A simple one-step method was used to prepare FeS/Fe3O4 co-modified biochar materials (FFB) that could activate PMS to degrade quinclorac (QNC) with a removal rate of 100%, even exhibiting optimum degradation of QNC reached 99.31% in irrigation water, demonstrating excellent anti-interference performance for co-existing anions and natural organic matter. Meanwhile, ecotoxicity analysis showed that the toxicity of degradation intermediates was lower than that of QNC. Characterization results demonstrated the even distribution of FeS and Fe3O4 onto biochar, supplying abundant Fe2+ to activate PMS producing reactive oxygen species (ROS), while the generated Fe3+ after reactive continue to be reduced with sulfur species to promote the cycle of Fe2+/Fe3+. The coexistence of ·OH, SO4·-, 1O2, and O2·- in the FFB/PMS-QNC system suggest the possession of two pathway with free radical and non-free radical pathways to degrade QNC. The density functional theory (DFT) was used to analyze the adsorption sites and adsorption energy of PMS, as well as the differential charge density, which further proved the generation of SO4·-, O2·- and 1O2. In addition, the electrochemical test results showed that electron transfer also played an important role in the degradation of QNC. This study provides a feasible approach for the removal of organic pollutants in actual water.

New insight into the activation mechanism of hydrogen peroxide by greigite (Fe3S4) for benzene removal: The combined action of dissolved and surface bounded ferrous iron

Iron sulfides have attracted growing concern in heterogeneous Fenton reaction. However, the structure of iron sulfides is different from that of iron oxides and how the structures affect the activation property of hydrogen peroxide (H₂O₂) remains unclear. This study investigated benzene removal through the activation of H₂O₂ by the synthesized magnetite (Fe₃O₄) and greigite (Fe₃S₄). The structures of Fe₃O₄ and Fe₃S₄ were characterized by XRD and EPR, the electron transfer properties of Fe₃O₄ and Fe₃S₄ were analyzed by electrochemical workstation, XPS and DFT. It is revealed that the effective benzene removal rate of 88.86％ in the Fe₃S₄/H₂O₂ was achieved, which compared to 15.58％ obtainable from the Fe₃O₄/H₂O₂, with the apparent rate constant in the Fe₃S₄/H₂O₂ being approximately 65 times over that in the Fe₃O₄/H₂O₂. The better H₂O₂ activation by Fe₃S₄ was attributed to the significant roles of S (-II) and S vacancies in regulating the dissolution of ferrous iron ions, thus generating abundant free •OH radical. In addition, surface bounded ferrous iron of Fe₃S₄ could transfer more electrons to H₂O₂ and O₂ to generate more surface bounded •OH and •O₂^-. This study revealed the combined action of dissolved and surface bounded ferrous iron of greigite on H₂O₂ activation, and provides an efficient heterogeneous H₂O₂ activator for the remediation of organic contaminants in groundwater.

FeMoS2 micoroparticles as an excellent catalyst for the activation of peroxymonosulfate toward organic contaminant degradation

The FeMoS₂ catalyst for activating peroxymonosulfate (PMS) is a promising pathway for removing organic pollutants in wastewater, however, the dominant FeS₂ phases and sulfur (S) vacancies in it are little involved. Herein, for the first time, novel bimetallic FeMoS₂ microparticles were synthesized by a simple method and then applied for PMS activation for degrading organic pollutants. The catalysts were characterized by several techniques, including X-ray diffraction and X-ray photoelectron spectroscopies. The results revealed that new FeMoS₂ microparticles containing S vacancies in the main FeS₂ phases were obtained. FeS₂ and S vacancies were found to play important roles for activating PMS by radical and nonradical pathways. More Fe²⁺ and Mo⁴⁺ were formed in the presence of S vacancies, which offered a new strategy for exploring novel heterogeneous catalysts in the activation of PMS for environmental remediation.

Modified birnessite MnO2 as efficient Fenton-like catalysts through electron transfer process between the simultaneously surface-activated peroxymonosulfate and pollutants

The development of efficient and eco-friendly Mn-based hybrids for the degradation of biorefractory organic pollutants via peroxymonosulfate (PMS) activation is highly desired. In this study, a novel graphite nanosheet (GNs)-based Fe-Mn bimetallic oxide (Fe doped birnessite MnO₂, FeMn/GNs) was synthesized under mild conditions. Compared with monometallic Fe or Mn oxide on GNs, FeMn/GNs exhibited a higher surface area, decreased Mn oxidation states, stronger interaction with GNs, and more active sites for PMS adsorption. Among different Fe/Mn ratios, Fe₂Mn₁/GNs showed the optimum performance for bisphenol A (BPA) degradation with the first-order rate constant of 0.22 min^-1, which was about 8.5 and 12.9 times higher than that of Mn/GNs and Fe/GNs, respectively. Different from the pollutant-catalyst-PMS electron transfer mechanism for Mn/GNs, the direct two-electron transfer in FeMn/GNs+PMS system, was mainly processed between the simultaneously activated BPA and PMS. This was probably based on the double adsorption sites of Fe and Mn species on the same catalyst: PMS was adsorbed by Fe species through hydroxyl groups, while BPA was mainly coordinated with Mn species due to the layered structure and hydrophobicity of the Mn oxide. This study is expected to provide the rational design of efficient Mn-based hybrids for PMS activation.

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

Benzoquinone (BQ) is of great significance for enhancement of contaminants degradation in the homogeneous oxidation system of peroxymonosulfate (PMS). However, the role of BQ in the heterogeneous activation of PMS for contaminants oxidation is still not clear. Herein, this work reported that the addition of BQ into the Fe₃S₄/PMS system could effectively enhance the degradation and mineralization of bisphenol A (BPA). Mechanistic study uncovered that the BQ and PMS would form active complexes (BQ-PMS*) on the surface of Fe₃S₄ and the excited BQ-PMS* can oxidize the BPA. To be specific, the electron of BPA was extracted by BQ-PMS* and then transfer to the surface of Fe₃S₄. The surface electron can induce the change of valence state of S and Fe elements, which can trigger the degradation of BPA and inhibit the decomposition of BQ itself. To the best of our knowledge, it is the first time to unveil the positive role of BQ in the heterogeneous activation of PMS, which may shed new light on the establishment of high-efficient PMS-based oxidation technology for remediation of organic pollutant.

Effects of organics concentration on the gravity-driven membrane (GDM) filtration in treating iron- and manganese-containing surface water

Iron and manganese contamination in the surface water is posing great challenges to the drinking water treatment supply, especially in the complex cases of organics involvement. Gravity-driven membrane (GDM) filtration equipped with the dual functions of ultrafiltration and biocake layer, conferred promising potentials in the removals of iron and manganese. This study evaluated the effects of organics concentrations on the removal performance of iron and manganese, as well as on the flux stabilization during GDM long-term filtration. The results indicated that stable flux level and the removal efficiency of manganese initially increased with the increase of organics concentration in the feed water, and then decreased. The moderate concentration of organic compounds in the feed water would positively facilitate the microbial activities and benefit to engineering a heterogeneous and porous biocake layer on the membrane surface, contributing to the highest improvements of stable flux (6.3 L m^-2 h^-1), while high concentration of organic compounds in the feed water would result in the increase in the thickness and EPS concentration of the biocake layer, leading to a flux reduction. Furthermore, the moderate concentration of organic compounds in the feed water was also beneficial to the manganese removal (> 94.6%) due to the more accumulation of auto-catalytic oxidation manganese oxides (MnOx) within the biocake layer and the improved biological degradation, however, further increase of organics concentration would deliver a negative impact on the manganese removal owing to the wrapping of MnOx by the organic substances. Overall, these findings provide practical and acceptable strategies to the selections of pre-treatments prior to GDM and promote its extensive application in treating the iron- and manganese-containing surface water.