Enhanced Removal of Chlorophene and 17β-estradiol by Mn(III) in a Mixture Solution with Humic Acid: Investigation of Reaction Kinetics and Formation of Co-oligomerization Products

Sustained Tl(I) removal by α-MnO2: Dual role of tunnel structure incorporation and surface catalytic oxidation

Manganese oxide-based filtration technologies are considered cost-effective for thallium (Tl) removal in engineered systems. However, current gaps in understanding the heterogeneous adsorption and oxidation mechanisms of typical tunneled α-MnO2 may lead to a serious underestimation of its long-term Tl removal potential. In this study, α-MnO2 could continuously remove Tl(I) during the 584-h reaction, with its irreversible removal eventually increasing to 81 %-95 % in different anionic environments. The adsorbed low-loaded Tl(I) is preferentially oxidized, whereas the high-loaded Tl tends to be adsorbed in a nonoxidative pathway by α-MnO2. The nonoxidized Tl(I) was gradually immobilized in the stable thalliomelane-like tunnel structure. More importantly, the synergism of surface Mn(III)-oxygen vacancies (Ov) on α-MnO2 could catalyze the oxidation of Tl(I). Furthermore, the oxidized Tl(III) was bound to the tunnel surface via double edge-sharing and double corner-sharing. In addition, the phosphate anion occupied the surface active site and inhibited the oxidation of Tl(I), thereby reducing the binding strength of Tl. This study provides a new perspective on the effectiveness and stability of Tl(I) removal by MnO2 and highlights the neglected mechanism of Mn(III)-Ov mediating Tl(I) oxidation, which expands our understanding of the removal and transformation fate of Tl in MnO2-engineered systems.

Facet-induced fractionation of humic acid by hematite and the promoted-photodegradation of 17β-estradiol catalyzed by hematite-humic complex

Hematite is a ubiquitous mineral with different dominant facets in the environment, which could adsorb humic acids (HA) to form photoactive hematite-HA complex. In this study, we prepared hematite nanocubes (HNC), hematite nanoplates (HNP) and hematite nanorhombs (HNR) with dominant facets as {012}, {001} and {104}, respectively. The abilities of the three hematites to adsorb and fractionate HA were compared. Our results indicated that the components with low molecular weight, high aromaticity and more oxygenated functional groups of HA were preferentially adsorbed. The fractionation degree followed the order of HNP > HNR > HNC, attributing to the coordination ability of different hematites. After hematite formed complexes with HA, it could promote the photodegradation of 17β-estradiol under visible light. The photoactivities of the three hematite-HA complexes were also compared. Since HNP adsorbed the most photochemically active HA components, HNP-HA showed the strongest enhancement for the degradation of 17β-estradiol. During the photodegradation process, the excited triplet state of HA (3HA*) and superoxide radical (O2•-) were identified as the dominant reactive species. Our results provide new insights into the role of hematite facets towards adsorption and fractionation of HA and photodegradation of co-existing contaminants, which would improve the understanding of the fate of pollutants in the presence of hematite and HA.

Unique role of Mn(II) in enhancing electro-oxidation of organic pollutants on anodes with low oxygen evolution potential at low current density

This study systematically explored the role of Mn(II) in the removal of 4-chlorophenol (4-CP) by electro-oxidation (EO) employing anodes with low oxygen evolution potential (OEP), i.e., Ti/RuO2-IrO2, Ti/Pt, and Ti/Ti4O7, as well as anodes with high OEP, namely, Ti/PbO2, Ti/SnO2, and boron-doped diamond (Si/BDD). Mn(II) significantly promoted 4-CP removal on the anodes with low OEP at fairly low current density (0.04 to 1 mA/cm2), but had minimal to negative impact on those with high OEP. Cyclic voltammetry and X-ray photoelectron spectra revealed that Mn(II) was oxidized to Mn(III), then to Mn(IV) on the anodes with low OEP, whereas its was oxidized directly to Mn(IV) on those with high OEP. Deposition of manganese oxide on the anodes with low OEP suppressed oxygen evolution reaction (OER) in EO process, but enhanced OER on those with high OEP. Quenching and spectral results consistently indicated that Mn(III) and Mn(IV) were the primary species responsible for enhancing 4-CP removal on the anodes with low OEP. These findings provide mechanistic insights into the redox transformation of Mn(II) in EO and the theoretical basis for a novel strategy to boost pollutant degradation in EO systems using low OEP anodes through coupling with the redox chemistry of manganese.

High-Valence Mn MOF Inspired by Laccase Mediators Enables Versatile Nature-Mimicking Catalysis

In nature, active Mn3+ -ligand complexes produced by laccase catalyzed oxidation can act as the low-molecular mass, diffusible redox mediators to oxidize the phenolic substrates overcoming the limitations of natural enzymes. Learning from the metal-ligand coordination of natural functional units, high-valence Mn metal-organic framework (Mn MOF) is constructed to simulate the catalysis in natural mediator system. Benefiting from the characteristics of nanoscale size, rich metal coordination unsaturated sites, and mixed valence state dominated by Mn(III), Nano Mn(III)-TP exhibits superior laccase-mimicking activity, whose Vmax (maximal reaction rate) is much higher than that of natural laccase. Referring to natural systems, relevant free radical experiments prove that the material induces the production of active oxygen species with the assistance of carboxylic acid, and active oxygen species further oxidize phenolic substrates. Based on its robust performances, the primary oxidative degradation of an emerging pollutant triclosan (TCS) is creatively applied, an important antiasthmatic medicine terbutaline sulfate (TBT) detection, and the synthesis of non-toxic and black near-natural dyes for dyeing. By simulating the essential mediators of natural enzymatic catalysis, an Mn MOF-based material that demonstrates multiple novel applications is successfully developed, which introduces a new reliable strategy for achieving versatile nature-mimicking catalysis.

The substantial generation of photochemically produced reactive intermediates (PPRIs) in algae-type zones from one large shallow lake promoted the removal of organic pollutants

Photochemically produced reactive intermediates (PPRIs) are ubiquitously present in aquatic systems and hold significant importance in biogeochemical cycles. The photochemical reaction of dissolved organic matter (DOM), known as photosensitizers upon irradiation, is the main pathway for PPRIs generation. However, the PPRIs produced by algal-derived organic matter (ADOM) and their environmental effects remains elusive. This study confirmed that substantial PPRIs were generated by ADOM in the algal-derived areas. UV absorption spectra, fluorescence spectra and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were then indicated a significant correlation between the molecular weight of DOM and the quantum yield of PPRIs, with lower molecular weight of DOM exhibiting a higher potential for PPRIs generation. Orthogonal partial least squares (OPLS) were used to build novel multivariate predictive models for indicating the PPRIs production in algae-type zone. Also, the higher concentrations of PPRIs could significantly removal different kinds of organic pollutants, such as bisphenol A (BPA), sulfadiazine (SDZ) and 17α-ethinylestradiol (EE2). Quenching experiments further elucidated that 3DOM⁎ was the key specie for pollutants degradation, serving as the precursor to generate a series of PPRIs. This study highlighted the importance of PPRIs generated from ADOM in the natural attenuation of pollutants and provided a new insight for understanding the self-purification in aquatic system.

Revisiting triplet state dissolved organic matter (3DOM⁎): Advances in probes, photoreactivity, and environmental implications

Triplet-state dissolved organic matter (3DOM⁎) plays a critical role in the photodegradation of organic pollutants in aquatic environments. This review offers a comprehensive overview of 3DOM⁎, focusing on monitoring methods using various probes, formation mechanisms, and photoreactivity. Traditional probes, such as 2,4,6-trimethylphenol (TMP) and sorbic acid, are widely used, while novel probes promise improved accuracy and sensitivity. The E2:E3 ratio emerges as a promising indicator for 3DOM⁎ due to its simplicity and correlation with photoreactivity, though further validation is needed to confirm its broader applicability. This review highlights the higher photoreactivity of DOM with low molecular weight, low aromaticity, and autochthonous sources, although DOM with contrasting features can also show significant photoreactivity. The presence of inorganic ions and nanomaterials significantly influences 3DOM⁎'s degradation capacity, demonstrating complex interactions with surrounding species. Additionally, the review underscores the importance of various environmental factors, including light source and DOM concentration, in affecting the photodegradation rates of contaminants. Recent literature suggests that future research should focus on developing new probes to capture different aspects of 3DOM⁎, exploring the synergistic effects of plastic leachate, and investigating the role of co-existing ions and nanomaterials on 3DOM⁎ activity. Employing machine learning (ML) techniques to predict 3DOM⁎-related parameters from easily measurable DOM descriptors presents an exciting research avenue. Enhanced understanding of 3DOM⁎ can lead to more effective strategies in wastewater treatment and environmental remediation.

Photochemical Transformation of Ibuprofen and Chlorophene Induced by Dissolved Organic Matter

Both ibuprofen (IBP) and chlorophene (CP) are frequently detected contaminants in surface aqueous environment. Dissolved organic matter (DOM) is an important component in water with high photo-reactivity, playing an important role in the transformation processes of various organic pollutants. This study systematically studied the influence of DOM on the photochemical transformation of IBP and CP by using humic acid as model DOM. In addition, the effect of inorganic salts on this process is also considered due to the high salt content in the ocean. Further quenching experiments and reactive oxygen species (ROSs) detection were also conducted to explore the reactive species acting on the IBP and CP transformation. Based on the products analysis and theoretical calculation, we proposed the IBP and CP transformation mechanism. Overall, this study provides some new insights into the transformation of organic pollutants in natural surface water, which is significant for assessing the fate of pollutants.

Role of low-molecular-weight organic compounds on photochemical formation of Mn(III)-ligands in aqueous systems: Implications for BPA removal

Aqueous trivalent manganese [Mn(III)], an important reactive intermediate, is ubiquitous in natural surface water containing humic acid (HA). However, the effect of low-molecular-weight organic acids (LMWOAs) on the formation, stability and reactivity of Mn(III) intermediate is still unknown. In this study, six LMWOAs, including oxalic acid (Oxa), salicylic acid (Sal), catechol (Cat), caffeic acid (Caf), gallic acid (Gal) and ethylene diamine tetraacetic acid (EDTA), were selected to investigate the effects of LMWOAs on the degradation of BPA induced by in situ formed Mn(III)-L in the HA/Mn(II) system under light irradiation. The chromophoric constituents of HA could absorb light radiation and generate superoxide radical to promote the oxidation of Mn(II) to form Mn(III), which was further involved in transformation of BPA. Our results implied that different LMWOAs did significantly impact on Mn(III) production and its degradation of BPA due to their different functional group. EDTA, Oxa and Sal extensively increased the Mn(III) concentration from 50 to 100 μM compared to the system without LMWOAs, following the order of EDTA > Oxa > Sal, and also enhanced the degradation of BPA with the similar patterns. In contrast, Cat, Caf and Gal had an inhibitory effect on the formation of Mn(III), which is likely because they consumed the superoxide radicals generated from irradiated HA, resulting in the inhibition of Mn(II) oxidation and further BPA removal. The product identification and theoretical calculation indicated that a single electron transfer process occurred between Mn(III)-L and BPA, forming BPA radicals and subsequent self-coupling products. Our results demonstrated that the LMWOAs with different structures could alter the cycling process of Mn via complexation and redox reactions, which would provide new implications for the removal of organic pollutants in surface water.

Dissolved organic matter accelerates microbial degradation of 17 alpha-ethinylestradiol in the presence of iron mineral

Dissolved organic matter (DOM) and iron minerals widely existing in the natural aquatic environment can mediate the migration and transformation of organic pollutants. However, the mechanism of interaction between DOM and iron minerals in the microbial degradation of pollutants deserves further investigation. In this study, the mechanism of 17 alpha-ethinylestradiol (EE2) biodegradation mediated by humic acid (HA) and three kinds of iron minerals (goethite, magnetite, and pyrite) was investigated. The results found that HA and iron minerals significantly accelerated the biodegradation process of EE2, and the highest degradation efficiency of EE2 (48%) was observed in the HA-mediated microbial system with pyrite under aerobic conditions. Furthermore, it had been demonstrated that hydroxyl radicals (HO•) was the main active substance responsible for the microbial degradation of EE2. HO• is primarily generated through the reaction between hydrogen peroxide secreted by microorganisms and Fe(II), with aerobic conditions being more conducive. The presence of iron minerals and HA could change the microbial communities in the EE2 biodegradation system. These findings provide new information for exploring the migration and transformation of pollutants by microorganisms in iron-rich environments.

Algal Extracellular Organic Matter Induced Photochemical Oxidation of Mn(II) to Solid Mn Oxide: Role of Mn(III)-EOM Complex and Its Ability to Remove 17α-Ethinylestradiol

Photosensitizer-mediated abiotic oxidation of Mn(II) can yield soluble reactive Mn(III) and solid Mn oxides. In eutrophic water systems, the ubiquitous algal extracellular organic matter (EOM) is a potential photosensitizer and may have a substantial impact on the oxidation of Mn(II). Herein, we focused on investigating the photochemical oxidation process from Mn(II) to solid Mn oxide driven by EOM. The results of irradiation experiments demonstrated that the generation of Mn(III) intermediate was crucial for the successful photo oxidization of Mn(II) to solid Mn oxide mediated by EOM. EOM can serve as both a photosensitizer and a ligand, facilitating the formation of the Mn(III)-EOM complex. The complex exhibited excellent efficiency in removing 17α-ethinylestradiol. Furthermore, the complex underwent decomposition as a result of reactions with reactive intermediates, forming a solid Mn oxide. The presence of nitrate can enhance the photochemical oxidation process, facilitating the conversion of Mn(II) to Mn(III) and then to solid Mn oxide. This study deepens our grasp of Mn(II) geochemical processes in eutrophic water and its impact on organic micropollutant fate.

Transformation of chlorobenzene by Mn(III) generated in MnO2/organic acid systems

Chlorobenzene (CB) is a prevalent organic contaminant in water and soil environments. It presents high chemical stability and is resistant to both oxidation and reduction. In this study, we showed that CB was substantially removed by soluble Mn(III) produced during the reductive dissolution of colloidal MnO2 by naturally-occurring organic acids such as formate (FOR), oxalate (OX), and citrate (CIT). The removal rate was dependent on the physicochemical properties of organic acids. With strong electron-donating and coordination ability, OX and CIT promoted MnO2 dissolution and Mn(III) generation compared to FOR, but had adverse effects on the stability and reactivity of Mn(III). As a result, CB removal followed the order: MnO2/CIT > MnO2/FOR > MnO2/OX. Analysis of the transformation products showed that Mn(III) complexes acted as strong electrophiles, attacking the ortho/para carbons of the benzene ring and transforming CB to chlorophenols via an electrophilic substitution mechanism. The theoretical foundation of this proposed reaction mechanism was supplemented by quantum mechanical calculations. Together, the findings of this study provide new insights into the transformation of CB in natural environments and hold the potential to offer a novel strategy for the development of manganese oxide/ligand systems for CB elimination.

Occurrence and cycle of dissolved iron mediated by humic acids resulting in continuous natural photodegradation of 17α-ethinylestradiol

17α-ethinylestradiol (EE2), a synthetic endocrine-disrupting chemical, can degrade in natural waters where humic acids (HA) and dissolved iron (DFe) are present. The iron is mostly bound in Fe(III)-HA complexes, the formation process of Fe(III)-HA complexes and their effect on EE2 degradation were explored in laboratory experiments. The mechanism of ferrihydrite facilitated by HA was explored with results indicating that HA facilitated the dissolution of ferrihydrite and the generation of Fe(III)-HA complexes with the stable chemical bonds such as C-O, CO in neutral, alkaline media with a suitable Fe/C ratio. 1O2, •OH, and 3HA* were all found to be important in the photodegradation of EE2 mediated by Fe(III)-HA complexes. Fe(III)-HA complexes could produce Fe(II) and hydrogen peroxide (H2O2) to create conditions suitable for photo-Fenton reactions at neutral pH. HA helped to maintain higher dissolved iron concentrations and alter the Fe(III)/Fe(II) cycling. The natural EE2 photodegradation pathway elucidated here provides a theoretical foundation for investigating the natural transformation of other trace organic contaminants in aquatic environments.

Potassium permanganate oxidation enhanced by infrared light and its application to natural water

Photocoupled permanganate (PM) is an effective way to enhance the oxidation efficiency of PM, however, the activation of PM by infrared has received little attention. This study aimed to investigate the ability of infrared light to activate PM. When coupled with infrared, the degradation rate of 4-chlorophenol (4-CP) is increased to 3.54 times of PM oxidation alone. The accelerated reaction was due to the formation of vibrationally excited PM by absorbing 3.1 kJ mol-1 infrared energy, which also leads to the primary reactive intermediates Mn(V/IV) in the reaction system. The infrared coupled PM system also showed 1.14-2.34 times promotion effect on other organic pollutants. Furthermore, solar composed of 45% infrared, coupled PM system showed excellent degradation performance, where the degradation of 4-CP in 10 L of tap water and river water was 68 and 23 times faster than in ultrapure water, respectively. The faster-increased degradation rate in natural waters is mainly due to the abundant inorganic ions, which can stabilize the manganese species, and then has a positive effect on 4-CP degradation. In summary, this work develops a energy-efficient photoactivated PM technology that utilizes infrared and provides new insights into the design of novel sunlight-powered oxidation processes for water treatment.

Covalent organic framework in-situ immobilized laccase for the covalent polymerization removal of sulfamethoxazole in the presence of natural phenols: Prominent enzyme stability and activity

In current water treatment processes, pollutants are typically degraded into small molecules and CO2 for detoxification. This study employed laccase-mediated aggregation of new pollutants with natural phenolic compounds to remove pollutants by forming large molecular substances, effectively sequestering carbon. Free laccase is susceptible to environmental influences, causing deactivation. However, immobilizing laccase onto a carrier enhances enzyme stability. In the experiment, laccase was immobilized onto the covalent organic framework TpPa-1 through an in-situ loading process, resulting in immobilized laccase Lac@TpPa-1. Stability studies revealed that immobilized laccase outperformed free laccase in terms of pH, temperature, and recyclability. Moreover, immobilized laccase was employed for catalyzing the removal of emerging pollutants containing natural phenolic compounds, achieving an 80.53% removal rate with the addition of 0.02 g of laccase within 5 h. Analytical techniques like Fourier-transform ion cyclotron resonance mass spectrometry were used to uncover reaction pathways, demonstrating the presence of radical polymerization and 1, 4 nucleophilic addition. This research utilized TpPa-1 as a carrier for laccase immobilization, promoting oxidation-induced polymerization for efficient pollutant removal. It provides a theoretical foundation for understanding the interplay between emerging pollutants and phenolic compounds in natural environments and enhances the practical application of laccase through immobilization.

Electrooxidation of chlorophene and dichlorophen by reactive electrochemical membrane: Key determining factors of removal efficiency

This study systematically investigated the variable main electrooxidation mechanism of chlorophene (CP) and dichlorophen (DCP) with the change of reaction conditions at Ti4O7 anode operated in batch and reactive electrochemical membrane (REM) modes. Significant degradation of CP and DCP was observed, that is, CP exhibited greater removal efficiency in batch mode at 0.5-3.5 mA cm-2 and REM operation (0.5 mA cm-2) with a permeate flow rate of 0.85 cm min-1 under the same reaction conditions, while DCP exhibited a faster degradation rate with the increase of current density in REM operation. Density functional theory (DFT) simulation and electrochemical performance tests indicated that the electrooxidation efficiency of CP and DCP in batch mode was primarily affected by the mass transfer rates. And the removal efficiency when anodic potentials were less than 1.7 V vs SHE in REM operation was determined by the activation energy for direct electron transfer (DET) reaction, however, the adsorption function of CP and DCP on the Ti4O7 anode became a dominant factor in determining the degradation efficiency with the further increase of anodic potential due to the disappeared activation barrier. In addition, the degradation pathways of CP and DCP were proposed according to intermediate products identification and frontier electron densities (FEDs) calculation, the acute toxicity of CP and DCP were also effectively decreased during both batch and REM operations.

Comparative study of the photooxidation of arsenite mediated by dissolved and mineral-associated humic acid under light irradiation

The photochemical processes of dissolved humic acid and its potential contribution to As(III) oxidation in natural water has received considerable attention. However, the role of mineral-humic complexes in As(III) conversion is rarely studied. Herein, two simulated mineral-humic complexes were prepared by coating humic acid on hydrous aluminum oxide, HA@HAO, or montmorillonite, HA@SWy, respectively, and batch experiments at circumneutral pH were performed under light irradiation. Our findings showed that the light-assisted oxidation of As(III) increased with increasing fractions of organic carbon in mineral-humic complexes, and As(III) photooxidation with HA@HAO or HA@SWy was up to 18.2 or 3.5-fold higher compared to that measured in the presence of equivalent amount of free HA, respectively. The reactive triplet state of HA and hydroxyl radicals in HA@HAO and HA@SWy system made a primary contribution to As(III) oxidation under irradiation. The results indicated that mineral-humic complexes have dual roles, an adsorbent and a photosensitizer, to promote As(III) access to reactive intermediates at the particle surfaces. This process was important for As(III) conversion in paddy water as colloidal particles, composed of both minerals and HA, could greatly promote As(III) oxidation and As(V) immobilization. This study provides a previously overlooked, important mechanism of As(III) phototransformation mediated by mineral-associated humic acid in natural environment.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17β-estradiol: Formation and contribution of reactive intermediates

In this study, humic acid (HA) enhanced 17β-estradiol (17β-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17β-E2 was increased from (14.414 ± 0.315) × 10-3 min-1 to (122.677 ± 1.729) × 10-3 min-1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2-) were the dominant RIs for 17β-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 > 1O2 > •O2-> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17β-E2 during the sonophotocatalytic process.

Algal organic matter and dissolved Mn cooperatively accelerate 17α-ethinylestradiol photodegradation: Role of photogenerated reactive Mn(III)

Algal extracellular organic matter (EOM), a major fraction of the dissolved organic matter found in eutrophic plateau lakes, can act as a photosensitizer to drive the abiotic oxidation of Mn(II). This process has the potential to generate reactive Mn(III) and influence the fate of organic pollutants. In this study, the photodegradation of 17α-ethinylestradiol (EE2) in the presence of Mn(II) and EOM was investigated with emphasis on the photogeneration mechanism of Mn(III). The results indicated that Mn(II) can accelerate EE2 photodegradation in EOM solution owing to the photogeneration of reactive Mn(III), and the enhancement was greater at higher Mn(II) concentrations. The generation of reactive Mn(III) was mainly attributable to the action of superoxide radical generated by photosensitization of EOM. In addition, the photodegradation of EE2 was slower at higher pH, possibly because of the deactivation of Mn(III) under alkaline conditions. Single-electron transfer was an indispensable process in the photodegradation. The differences in fluorophore content, pH, and NO₃^- concentrations are all important determinants for EE2 photodegradation in natural waters. The information obtained in this research would contribute to the understanding of reactions between Mn(II) and EOM, and provide new insights into the behaviors of reactive Mn(III) in eutrophic water irradiated by sunlight.

Mn(III)-mediated bisphenol a degradation: Mechanisms and products

Bisphenol A (BPA) is a high production volume chemical with potential estrogenic effects susceptible to abiotic degradation by MnO₂. BPA transformation products and reaction mechanisms with MnO₂ have been investigated, but detailed process understanding of Mn(III)-mediated degradation has not been attained. Rapid consumption of BPA occurred in batch reaction vessels with 1 mM Mn(III) and 63.9 ± 0.7% of 1.76 ± 0.02 μmol BPA was degraded in 1 hour at circumneutral pH. BPA was consumed at 1.86 ± 0.09-fold higher rates in vessels with synthetic MnO₂ comprising approximately 13 mol% surface-associated Mn(III) versus surface-Mn(III)-free MnO₂, and 10-35% of BPA transformation could be attributed to Mn(III) during the initial 10-min reaction phase. High-resolution tandem mass spectrometry (HRMS/MS) analysis detected eight transformation intermediates in reactions with Mn(III), and quantum calculations proposed 14 BPA degradation products, nine of which had not been observed during MnO₂-mediated BPA degradation, suggesting mechanistic differences between Mn(III)- versus MnO₂-mediated BPA degradation. The findings demonstrate that both Mn(III) and Mn(IV) can effectively degrade BPA and indicate that surface-associated Mn(III) increases the reactivity of synthetic MnO₂, offering opportunities for engineering more reactive oxidized Mn species for BPA removal.

Trade-off effect of dissolved organic matter on degradation and transformation of micropollutants: A review in water decontamination

The degradation of micropollutants by various treatments is commonly affected by the ubiquitous dissolved organic matter (DOM) in the water environment. To optimize the operating conditions and decomposition efficiency, it is necessary to consider the impacts of DOM. DOM exhibits varied behaviors in diverse treatments, including permanganate oxidation, solar/ultraviolet photolysis, advanced oxidation processes, advanced reduction process, and enzyme biological treatments. Besides, the different sources (i.e., terrestrial and aquatic, etc) of DOM, and operational circumstances (i.e., concentration and pH) fluctuate different transformation efficiency of micropollutants in water. However, so far, systematic explanations and summaries of relevant research and mechanism are rare. This paper reviewed the "trade-off" performances and the corresponding mechanisms of DOM in the elimination of micropollutants, and summarized the similarities and differences for the dual roles of DOM in each of the aforementioned treatments. Inhibition mechanisms typically include radical scavenging, UV attenuation, competition effect, enzyme inactivation, reaction between DOM and micropollutants, and intermediates reduction. Facilitation mechanisms include the generation of reactive species, complexation/stabilization, cross-coupling with pollutants, and electron shuttle. Moreover, electron-drawing groups (i.e., quinones, ketones functional groups) and electron-supplying groups (i.e., phenols) in the DOM are the main contributors to its trade-off effect.

Mitigation of ultrafiltration membrane fouling by a simulated sunlight-peroxymonosulfate system with the assistance of irradiated NOM

Oxidation pretreatments prior to ultrafiltration are hindered by the need for energy input and sludge disposal. Herein, a simulated sunlight-induced natural organic matter (NOM) for peroxymonosulfate (PMS) activation was used as pretreatment to alleviate ultrafiltration membrane fouling caused by NOM itself in the Songhua River water. When light intensity was over 100 mW/cm², the pretreatment removed NOM effectively, characterized with UV₂₅₄, dissolved organic carbon (DOC) and maximum fluorescent intensity (F_max), and improved filtration flux. At 200 mW/cm² light intensity and 0.5 mM PMS, 57.5% of UV₂₅₄ and 18.5% of DOC were removed, and humic-like fluorescent component was degraded by 84%-94% while ∼60% for protein-like substance. Membrane flux was increased by 94%, and reversible and irreversible fouling resistances were reduced by 62.4% and 51.9%, respectively. Both total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) were moderately correlated with the DOC, whereas they prominently correlated with the UV₂₅₄ and the F_maxs of all fluorescence components, which could be served as key indicators to predict and control membrane fouling. Mathematical modeling showed that the pretreatment alleviated the fouling in the membrane pores and cake layer. The simulated sunlight-induced NOM (³NOM* and e_aq^¯) could activate PMS to form active species, which enabled to oxidize high molecular weight (MW) substances and mineralize low MW compounds in NOM as well as hinder their linking with inorganic cations, thereby reducing organic and inorganic membrane fouling simultaneously. This study may provide a new strategy for decentralized potable water treatment, especially in a single household or community.

Generation of hydroxyl radicals via activation of Cr(VI) by UVA-LED for rapid decontamination: The important role of Cr(V)

Hexavalent chromium (Cr(VI)) was activated by ultraviolet-A light-emitting diode (UVA-LED), resulting in efficient removal of various pollutants, including dye, pharmaceuticals, and pesticides, with pseudo-first-order rate constants of 0.0610-0.159 min^-1. Comparatively, UVA-LED or Cr(VI) alone barely degraded selected pollutants. Both HO• and Cr(V) were produced in the UVA-LED/Cr(VI) system based on scavenging and probing experiments, UV-visible and electron spin resonance spectra analysis. HO• was demonstrated to be the dominant reactive species via stepwise regeneration of Cr(V) to Cr(VI). The quantum yield of HO• was determined to be 7.79 × 10^-4 mol Es^-1 at a Cr(VI) dosage of 0.5 mM and pH of 6.0. Additionally, the degradation efficiency of sulfamethoxazole (SMX) as a model compound decreased linearly as UVA-LED wavelengths increased from 365 to 405 nm, while SMX was barely degraded at visible light irradiation wavelength ranges (449-505 nm). SMX degradation efficiency increased from 71.0 % to 97.5 % as Cr(VI) dosage increased from 0.05 to 0.7 mM. pH displayed a negative impact on SMX degradation with its removal efficiency decreasing from 99.4 % to 13.3 % as pH increased from 3.0 to 9.0. This study first reported that HO• was generated via activation of Cr(VI) by UVA-LED, which is instructive for the removal of pollutants co-existed in chromium-containing wastewater.

Efficient degradation of alkyl imidazole ionic liquids in simulated sunlight irradiated periodate system: Kinetics, reaction mechanisms, and toxicity evolution

As a class of emerging aquatic pollutants, alkylimidazole-based ionic liquids (AM-ILs) have received extensive attention due to the large acute toxicity to aquatic organisms. Therefore, in order to protect both aquatic organisms and human beings, it is necessary to seek an efficient and environmental-friendly technology for removal of AM-ILs from water bodies. In this work, we found that under simulated sunlight (Xe lamp) irradiation, periodate (KIO₄, PI) could efficiently degrade 1-hexyl-2,3-dimethylimidazolium bromide ([HMMIm]Br), a representative AM-ILs with six carbon atoms in the side chain. Kinetics experiments on the degradation of [HMMIm]Br were performed, and the results showed that a high degradation efficiency (≥90.00%) of the cation ([HMMIm]⁺) was still maintained under harsh water conditions of strong acidity/alkaliny or with various non-target inorganic ions. More importantly, the anion of bromide ion (Br^-) was not oxidized to the carcinogenic bromate (BrO₃^-) in current reaction system. The excited stated PI (marked as PI*) was detected by Laser flash photolysis, and it was an important reactive species for [HMMIm]⁺ degradation. As rationalized by theoretical calculations and scavenging experiments, the main oxidation mechanisms of [HMMIm]⁺ were hydroxyl radicals induced substitution reaction, PI* initiated electron and double oxygen transfer, and direct photolysis mediated chemical bond cleavage reaction, which contributed to 73%, 21%, and 6% of [HMMIm]⁺ degradation, respectively. Moreover, toxicity evaluation by ECOSAR software indicated that the oxidation products were generally less toxic to three aquatic organisms (fish, water flea, and green algae) than the target molecule [HMMIm]Br. In conclusion, this work proposed novel oxidation mechanisms of sunlight-activated PI system, and the findings may inspire further researches on the application of photoactivated hypervalent acids in water purification.

Impact of manganese sulfide (MnS) oxygenation-induced oxidization on aqueous organic contaminants: Insight into the role of the hydroxyl radical (HO·)

Manganese sulfide (MnS) has unique reactive abilities and can affect the fate and toxicity of contaminants in the natural environment, specifically sulfidic sediments that undergo biogeochemical changes due to natural and artificial processes. However, the effect of oxidization induced by the oxygenation of MnS on organic contaminants remains poorly understood. Herein, we revealed that the hydroxyl radical (HO·) was the dominant reactive oxidant for the rapid degradation of the assessed hydrophobic organic contaminants (including azo dye, nitroaromatic compounds, pesticide, and an endocrine disrupt chemical) during the oxygenation of MnS based on the competitive dynamic experiments, quenching experiments and electron spin resonance (ESR) methods. The removal rates of the assessed organic contaminants were significantly dependent on MnS dosage and co-solutes, including sediment humic acid, metal ions (Mn²⁺and Fe³⁺), and inorganic anions (PO₄^3-and Cl^-). HO· scavenging by sulfide and its oxidation products (e.g., elemental sulfur), rather than dissolved Mn²⁺, was responsible for the low utilization efficiency of HO· for the assessed contaminants. The contribution of the manganese oxide (MnO₂) generated by the oxygenation of MnS to the examined degradation of contaminants could be neglected. Considered collectively, the reaction between H₂O₂ and MnO₂ generated superoxide radicals (O₂^-·) which dominated the generation of HO· in an oxic MnS suspension. The results suggest that the impact of oxidization induced by the oxygenation of MnS on environmental contaminants should be of concern in both natural and engineered systems.

Enhanced MnO2 oxidation of methotrexate through self-sensitized photolysis

MnO₂, which is ubiquitous in soil and sediment in natural water environments, may play an important role in the photolysis of contaminants by sunlight, but the interactions between MnO₂ and contaminants in aqueous environments under sunlight irradiation have not been investigated. In this study, the simultaneous presence of sunlight and MnO₂ significantly enhanced the degradation efficiency of methotrexate (MTX). Accordingly, we hypothesized that the overall enhancement of this synergistic reaction is due to the additional production of Mn(III) via MTX self-sensitized photolysis. The pseudo-first-order kinetic model for the photoreaction of MTX with MnO₂ (Light/MTX+MnO₂) during the initial reaction kinetics (0-2 h) revealed a rate constant of 0.43 h¹ ([MTX] = 20 μM, [MnO₂] = 200 μM, and pH = 7), which is faster than that obtained with sunlight alone (0.14 h¹) or MnO₂ alone; Mn(II) and Mn(III) were formed at concentrations of 24.3 ± 1.0 μM and 14.8 ± 1.4 μM, respectively. Dissolved Mn(III) species were identified as the main oxidant species responsible for the degradation of MTX. Two reaction pathways for the production of Mn(III) through Light/MTX+MnO₂ were proposed; MTX acts as a photosensitizer to produce ³MTX* responsible for the reduction of MnO₂ to Mn(III), whereas O₂^• participates in the oxidation of Mn(Ⅱ) to Mn(Ⅲ). Byproduct analysis demonstrated that the Mn(III) generated in the Light/MTX+MnO₂ system enhances C－N bond cleavage, ketonization, and hydrolysis pathways in the MTX transformation.

Degradation of Organic Contaminants by Reactive Iron/Manganese Species: Progress and Challenges

Many iron(II, III, VI)- and manganese(II, IV, VII)-based oxidation processes can generate reactive iron/manganese species (RFeS/RMnS, i.e., Fe(IV)/Fe(V) and Mn(III)/Mn(V)/Mn(VI)), which have mild and selective reactivity toward a wide range of organic contaminants, and thus have drawn significant attention. The reaction mechanisms of these processes are rather complicated due to the simultaneous involvement of multiple radical and/or nonradical species. As a result, the ambiguity in the occurrence of RFeS/RMnS and divergence in the degradation mechanisms of trace organic contaminants in the presence of RFeS/RMnS exist in literature. In order to improve the critical understanding of the RFeS/RMnS-mediated oxidation processes, the detection methods of RFeS/RMnS and their roles in the destruction of trace organic contaminants are reviewed with special attention to some specific problems related to the scavenger and probe selection and experimental results analysis potentially resulting in some questionable conclusions. Moreover, the influence of background constituents, such as organic matter and halides, on oxidation efficiency of RFeS/RMnS-mediated oxidation processes and formation of byproducts are discussed through their comparison with those in free radicals-dominated oxidation processes. Finally, the prospects of the RFeS/RMnS-mediated oxidation processes and the challenges for future applications are presented.

Mechanistic Study of the Effects of Agricultural Amendments on Photochemical Processes in Paddy Water during Rice Growth

The photochemical properties of paddy water might be affected by the commonly used amendments in rice fields owing to the associated changes in water chemistry; however, this important aspect has rarely been explored. We examined the effects of agricultural amendments on the photochemistry of paddy water during rice growth. The amendments significantly influenced the photogenerated reactive intermediates (RIs) in paddy water, such as triplet dissolved organic matter (³DOM*), singlet oxygen, and hydroxyl radicals. Compared with control experiments without amendments, the application of straw and lime increased the RI concentrations by up to 16.8 and 11.1 times, respectively, while biochar addition had limited effects on RI generation from paddy water in in situ experiments under sunlight. Fluorescence emission-excitation matrix spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and structural equation modeling revealed that upon the addition of straw and lime amendments, humified DOM substances contained lignins, proteins, and fulvic acids, which could produce more RIs under irradiation. Moreover, the amendments significantly accelerated the degradation rate of 2,4-dichlorophenol but led to the ³DOM*-mediated formation of more toxic and stable dimeric products. This study provides new insights into the effects of amendments on the photochemistry of paddy water and the pathways of abiotic degradation of organic contaminants in paddy fields.

Visible light promoted the removal of tetrabromobisphenol A from water by humic acid-FeS colloid

Ferrous sulfide (FeS) and humic acid (HA) are typical black substances in black bloom water. Based on the strong reduction ability of FeS and the photosensitivity of HA, the transformation of toxic organic pollutants by the combination of FeS and HA (HA-FeS) is not clear. In order to explore this issue, the stability of HA-FeS was analyzed by measuring the hydrodynamic diameter and zeta potential of HA-FeS, and then the removal mechanism and possible degradation pathway of tetrabromobisphenol A (TBBPA) by HA-FeS under continuous illumination were discussed. The results showed that the hydrodynamic diameter of FeS was reduced and the stability of FeS was improved, and it was easily suspended after FeS combined with the HA in the water. The combination of HA and FeS promoted the removal of TBBPA in water, no matter it was in the presence or absence of light. Besides, compared with the absence of light, the removal efficiency of TBBPA was improved by HA-FeS with continuous light. There were two reasons for the increase in the removal efficiency of TBBPA by HA-FeS. On the one hand, Fe²⁺ and S^2- of HA-FeS had more stable chemical valence and obtained better reducibility under continuous light than that in the dark. On the other hand, light induced the release of active species (O₂^-, ¹O₂, and OH) in the HA-FeS composite colloid and further promoted the degradation of organic pollutants. Therefore, the black substances (FeS) of black blooms may play a beneficial role in the removal of pollutants under sunlight.

Insight into enhanced activation of permanganate under simulated solar irradiation: Rapid formation of manganese species

Herein, permanganate [Mn(VII)] was activated by simulated solar (SS) (SS/Mn(VII)), resulting in rapid degradation of micropollutants in several minutes, with rates of target micropollutants outnumbered those in the Mn(VII) alone and SS. To explore the mechanism in this process, 4-cholorphenol (4-CP), p-hydroxybenzoic acid (p-HBA), and enrofloxacin (ENR) were selected as model compounds. Lines of evidence indicated that reactive manganese species (RMnS) (i.e., Mn(III) and Mn(V)) rather than radicals from Mn(VII) photolysis participated in the conversion of model compounds. Interestingly, roles of RMnS differed among three model compounds, suggesting their selectivity toward micropollutants. Increasing Mn(VII) dosage proved greater micropollutant degradation, while impacts of pH on SS/Mn(VII) performance varied among model compounds. P-HBA and ENR showed the lowest degradation efficiency at alkaline, whereas 4-CP demonstrated the best performance at alkaline, indicating the reactivity of RMnS varied toward micropollutants at different pH values. The quantum yield of Mn(VII) was 8.36 ± 0.03 X 10^-6 mol Einstein^-1 at pH 7.0. Effects of common co-existing constituents (Cl^-, HCO₃^-, and humic acid (HA)) on micropollutant degradation by SS/Mn(VII) were examined. Specifically, HCO₃^- positively influenced the 4-CP and p-HBA degradation, whereas ENR was not affected, likely owing to the selectivity of RMnS-HCO₃^- complexes. HA was conducive to degrade p-HBA due to the production of RMnS-HA complexes, but unfavorable for ENR and 4-CP degradation because of the competitive light absorption and Mn(VII). Furthermore, a number of degradation products of 4-CP, p-HBA, and ENR were identified and possible pathways were proposed accordingly. The effectiveness of this process for micropollutant degradation in real waters, natural sunlight, ultraviolet and visible light via cut-off filtering SS emission was confirmed. This work revealed a great potential of applying SS/Mn(VII) for the marked degradation of micropollutants and facilitated the understandings of Mn(III)/Mn(V) behaviors.

Accurate Removal of Trace 17β-Estradiol and Estrogenic Activity in Blended Systems under a Photoelectrocatalytic Circulating Flow

Trace 17β-estradiol (E2) is persistent against advanced treatment when blended with higher concentrations of low-toxicity organics, thus wasting energy. A circulating-flow selective photoelectrocatalysis (CF-SPEC) system is established with a selective E2-TiO₂-NR photoanode, accurately reducing 1 μg L^-1 E2 to less than 0.1 ng L^-1 along with eliminating estrogenic activity even when blended with natural organic matter (NOM) at a thousand times higher concentration. Such high efficiency is derived from the augmented selectivity and activity of E2-TiO₂-NRs toward E2 during CF-SPEC. Under a flow, the difference in adsorption capacity between NOM and E2 is further amplified 5.6-fold. Furthermore, the higher initial ^•OH concentration and faster mass transfer jointly endow CF-SPEC with a stronger oxidation capacity. As a result, the removal of E2 increases by 58.7%, and the elimination of estrogenic activity increases 5.8-fold. In addition, deeper mineralization and less homo- and heterocoupling under CF-SPEC are observed, leading to more thorough estrogenic activity removal. Although additional energy is needed to maintain the flow, there is a 55% decrease in energy consumption due to the accurate removal capacity. This work suggests a combination of flow degradation and surface engineering that can be expanded for the selective removal of toxic trace pollutants in blended systems.

Oxidative transformation of emerging organic contaminants by aqueous permanganate: Kinetics, products, toxicity changes, and effects of manganese products

Permanganate (Mn(VII)) has been widely studied for removal of emerging organic contaminants (EOCs) in water treatment and in situ chemical oxidation process. Studies on the reactive intermediate manganese products (e.g., Mn(III) and manganese dioxide (MnO₂)) generated from Mn(VII) reduction by EOCs in recent decades shed new light on Mn(VII) oxidation process. The present work summarizes the latest research findings on Mn(VII) reactions with a wide range of EOCs (including phenols, olefins, and amines) in detailed aspects of reaction kinetics, oxidation products, and toxicity changes, along with special emphasis on the impacts of intermediate manganese products (mainly Mn(III) and MnO₂) in-situ formed. Mn(VII) shows appreciable reactivities towards EOCs with apparent second-order rate constants (k_app) generally decrease in the order of olefins (k_app = 0.3 - 2.1 × 10⁴ M^-1s^-1) > phenols (k_app = 0.03 - 460 M^-1s^-1) > amines (k_app = 3.5 × 10^-3 - 305.3 M^-1s^-1) at neutral pH. Phenolic benzene ring (for phenols), (conjugated) double bond (for olefins), primary amine group and the N-containing heterocyclic ring (for amines) are the most reactive sites towards Mn(VII) oxidation, leading to the formation of products with different structures (e.g., hydroxylated, aldehyde, carbonyl, quinone-like, polymeric, ring-opening, nitroso/nitro and C-N cleavage products). Destruction of functional groups of EOCs (e.g., benzene ring, (conjugated) double bond, and N-containing heterocyclic) by Mn(VII) tends to decrease solution toxicity, while oxidation products with higher toxicity than parent EOCs (e.g., quinone-like products in the case of phenolic EOCs) are sometimes formed. Mn(III) stabilized by model or unknown ligands remarkably accelerates phenolic EOCs oxidation by Mn(VII) under acidic to neutral conditions, while MnO₂ enhances the oxidation efficiency of phenolic and amine EOCs by Mn(VII) at acidic pH. The intermediate manganese products participate in Mn(VII) oxidation process most likely as both oxidants and catalysts with their generation/stability/reactivity affecting by the presence of NOM, ligand, cations, and anions in water matrices. This work presents the state-of-the-art findings on Mn(VII) oxidation of EOCs, especially highlights the significant roles of manganese products, which advances our understanding on Mn(VII) oxidation and its application in future water treatment processes.

Photoproduction Rates of One-Electron Reductants by Chromophoric Dissolved Organic Matter via Fluorescence Spectroscopy: Comparison with Superoxide and Hydrogen Peroxide Rates

One-electron reductants (OER) photoproduced by chromophoric dissolved organic matter (CDOM) have been shown to be likely precursors for the formation of superoxide and subsequently hydrogen peroxide. An improved method that employs a nitroxide radical probe (3AP) has been developed and utilized to determine the photoproduction rates of OER from a diverse set of CDOM samples. 3AP reacts with OER to produce the hydroxylamine, which is then derivatized with fluorescamine and quantified spectrofluorometrically. Although less sensitive than traditional methods for measuring R_O2•-, measuring R_H provides a simpler and faster method of estimating R_O2•- and is amenable to continuous measurement via flow injection analysis. Production rates of OER (R_H), superoxide (R_O2•-), and hydrogen peroxide (R_H2O2) have a similar wavelength dependence, indicating a common origin. If all the OER react with molecular oxygen to produce superoxide, then the simplest mechanism predicts that R_H/R_H2O2 and R_O2•-/R_H2O2 should be equal to 2. However, our measurements reveal R_H/R_H2O2 values as high as 16 (5.7-16), consistent with prior results, and R_O2•-/R_H2O2 values as high as 8 (5.4-8.2). These results indicate that a substantial fraction of superoxide (65-88%) is not undergoing dismutation. A reasonable oxidative sink for superoxide is reaction with photoproduced phenoxy radicals within CDOM.

Interfacial reaction between organic acids and iron-containing clay minerals: Hydroxyl radical generation and phenolic compounds degradation

Reactive oxygen species, especially hydroxyl radicals (OH), exert a distinguished role in the transformation of contaminants, and their in-situ generation attracts wide attentions in environmental and geochemical areas. The present work explored the potential formation of OH during the interactions between iron-containing clay minerals and environmentally prevalent organic acids in dark environments. The results demonstrated that the accumulative OH concentrations were related to the solution pH, the types of clay minerals, and the nature of organic acid species. At pH 5.5, 1.2- 15.2 times of OH were generated from the reduction of Na-nontronite-2 (Na-NAu-2) compared with other clay minerals in the presence of ascorbic acid (AA) at 144 h. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) analyses indicated that Fe(III) was reduced to Fe(II) by AA during OH formation. Meanwhile, chemical probe tests coupled with quenching experiments confirmed the generation of H₂O₂ and superoxide radical (O₂^-), which participated in the formation of OH. The produced OH/O₂^- can transform 68.4%, 86.4%, and 50.1% of phenol, p-nitrophenol, and 2,4-dichlorophenol within 168 h in AA-Na-NAu-2 suspension, respectively. This work provides valuable insights into OH production in the mutual interaction between organic acids and iron-bearing clays, which is helpful for the development of a new method for removing organic pollutants from contaminated water and soil environments.

Fungal laccase-triggered 17β-estradiol humification kinetics and mechanisms in the presence of humic precursors

Naturally-occurring phenolic acids (PAs) act as humic precursors that participate in the conversion behaviors and coupling pathways of steroidal estrogens (SEs) during laccase-triggered humification processes (L-THPs). Herein, the influences and mechanisms of PAs on Trametes versicolor laccase-evoked 17β-estradiol (E2) conversion kinetics and humification routes were explored. Fungal laccase was fleet in converting > 99% of E2, and the calculated pseudo-first-order velocity constant and half-time values were respectively 0.039 min^-1 and 17.906 min. PAs containing an O-dihydroxy moiety such as gallic acid and caffeic acid evidently hampered E2 humification owning to the yielded highly reactive O-quinones reversed E2 radicals by hydrogen transfer mechanism, implying that the inhibition effect was enormously dependent upon the number and position of the phenolic -OH present in humic precursors. Oligomers and polymers with carbon-carbon/oxygen links were tentatively found as E2 main humified species resulting from laccase-evoked successive oxidative-coupling. Note that PAs participating in the humification also encountered oxydehydrogenation, self-polymerization, and cross-binding to E2. Interestingly, the -COOH and -OCH₃ groups of PAs could be deprived in radical-caused self/co-polymerization. The generation of humified products not only circumvented the environmental risks of parent compounds but accelerated global carbon sequestration. To our knowledge, this is the first in-depth revelation of the humification pathways and related mechanisms of SEs with humic precursors in aquatic ecosystems by L-THPs.

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.

Enhanced and selective phototransformation of chlorophene on aluminum hydroxide-humic complexes

Mineral-humic complexes, known as mineral-associated organic matter (MAOM), are ubiquitous in natural waters. However, the interaction between organic pollutants and MAOM remains elusive, which may affect their degradation process. In this study, photochemical transformation of chlorophene (CP) in the presence of MAOM, prepared by coating aluminum hydroxide with humic acid (HA-HAO), was investigated. Our results showed that the degradation of CP was significantly enhanced in the presence of HA-HAO, and the degradation rate constant was ~5 times as that with HA only. It was because the adsorption of CP to HA-HAO particles was greatly enhanced, and concentration of reactive oxygen species (ROS) was increased on HA-HAO surfaces, which further promoted the reactions between CP and ROS. The quenching experiments combined with EPR technology confirmed that superoxide anion (O₂^·-) was the primary reactive radical on CP photodegradation. More importantly, the degradation of CP with HA-HAO followed a hydroxylation process, rather than the oligomerization reaction with HA only. Spectroscopic analysis provided direct evidence for the formation of hydrogen bonding between CP phenolic hydroxyl group and surface oxygen of HAO, which would suppress the reactivity of phenolic hydroxyl group, consequently the ortho- and meta-positions of CP became more facile for the hydroxylation reaction. This study shows the importance of MAOM in altering the photochemical behavior and transformation pathway of organic contaminants.

Lignocellulose Biomass as a Multifunctional Tool for Sustainable Catalysis and Chemicals: An Overview

Today, the theme of environmental preservation plays an important role within the activities of the scientific community and influences the choices of politics and the common population. In this context, the use of non-fossil substances should be promoted for different reasons: to avoid the depletion and damage of the areas involved in the fossil fuel extraction, decrease the impact of emissions/by-products related to the industrial transformation of fossil-based products and possibly exploit residual biomasses as sources of carbon. This latter aspect also can be viewed as a way to revalorize lignocellulose waste, generally destined to dump as putrescible matter or to be incinerated. In this review, we are aiming to present a concise overview of the multiple functions of lignocellulose biomass in the broad field of catalysis for a sustainable development. The originality of the approach is considering the lignocellulose-derived matter in three different aspects: (i) as a precursor to convert into platform molecules, (ii) as an active material (i.e., humic-like substances as photosensitizers) and (iii) as a green support for catalytic applications. We find that this perspective can widen the awareness level of scientists involved in the catalysis field for the exploitation of residual biomass as a valuable and complementary resource.

Degradation of Atrazine, Simazine and Ametryn in an arable soil using thermal-activated persulfate oxidation process: Optimization, kinetics, and degradation pathway

This study examined the feasibility of applying thermal-activated persulfate (PS) oxidation for remediation of soil co-contaminated with s-triazine herbicides including Atrazine (ATZ), Simazine (SIM) and Ametryn (AME). Homogeneous activation using heating method (50 °C) was selected. Results showed that thermal-activated PS oxidation process may successfully degrade ATZ in soil and degradation efficiency was increased along the arising activation temperature. Higher PS dosages and depressed initial pH were beneficial for degradation while increasing initial ATZ concentration may hamper the degradation. The oxidation process may lead to changes of surface functional groups on soil. The presence of Cl^-, HCO₃^- and H₂PO₄^- at both of low and high concentrations may inhibit the degradation of ATZ. Soil depths may apparently influence the ATZ degradation which followed 0-10 < 10-30 < 30-60 cm mainly depending on the soil organic matter (SOM) contents. Thermal-activated PS may effectively degrade ATZ, SIM and AME under co-contaminated condition and the more favorable of ethyl group towards SO₄^- than isopropyl and methylation groups was detected. Both of SO₄^- and HO were identified to be responsible for degradation. Finally, degradation intermediates of ATZ, SIM and AME were identified by LC-Q-TOF-MS and detailed transformation pathways for three pesticides were proposed, respectively.

Oxidation of Mn(III) Species by Pb(IV) Oxide as a Surrogate Oxidant in Aquatic Systems

Dissolved Mn(III) species have been recognized as a significant form of Mn in redox transition environments, but a holistic understanding of their geochemical properties still lacks the characterization of their reactivity as reductants. Through using PbO₂ as a surrogate oxidant and pyrophosphate (PP) as a model ligand, we evaluated the thermodynamic and kinetic constrains of dissolved Mn(III) oxidation under environmentally relevant pH. Without disproportionation, Mn(III) complexes could be directly oxidized by PbO₂ to produce Mn oxides. The reaction rates decreased with increasing PP:Mn(III) ratio and became negligible when the ratio was above a threshold value. Particulate manganite could also be oxidized by PbO₂ with detectable production of Pb(II). The favorability of Mn(III) oxidation by PbO₂ as a function of the PP:Mn ratio could be predicted by the stability constant of the Mn(III)-PP complex. We developed kinetic models that couple multiple pathways of Mn oxidation by PbO₂ to simulate the dynamics of Pb release, loss of dissolved Mn, as well as Mn(III) production and consumption. Beyond the context of Mn geochemistry, the interactions between Pb and various Mn species, including its trivalent forms, may also have important implications to the water quality in lead service lines within distribution systems.

Influence of humic acids on fungal laccase-initiated 17α-ethynylestradiol oligomerization: Transformation kinetics and products distribution

Fungal laccase has aroused great concern in rapidly removing estrogens because of its ability to accelerate humification and oligomerization. Here, the effect of two humic acids (HAs) on the reaction kinetics and products distribution of 17α-ethynylestradiol (EE2) in laccase-initiated humification and coupling was systematically elucidated. Laccase from Trametes versicolor exhibited over 98.3% removal rate for EE2 at pH 5.0 within 120 min, while HAs invariably restrained EE2 transformation by competing with target-substrate for the enzymatic catalytic center. EE2 removal followed pseudo-first-order kinetics, and the rate constant was decreased markedly with increasing concentration of two HAs (0-60 mg L^-1). Additionally, laccase heightened the aromaticity and humification degrees (A_{250 nm}/A_{365 nm} ratio) of HAs probably due to the formation of new humic polymers such as (HA)_m and/or (HA)_m-(EE2)_n (m and n represent the number of HA and EE2 units, respectively). Three major EE2 oligomers were identified, in accordance with a mechanism involving the phenoxy radical-driven polymerization to yield a wide variety of self-coupling products. Notably, HAs diminished the extent of EE2 self-coupling but aggrandized the cross-coupling between EE2 and HAs, and the inhibition degree of EE2 self-coupling increased with the concentration of HAs. One major reason is EE2 could be covalently incorporated into humic molecules to produce (HA)_m-(EE2)_n cross-coupling products via radical-caused C-C, C-O-C, and/or C-O-C bonds, thereby reducing EE2 self-oligomerization. These findings highlight that HAs play a vital role in the fungal laccase-induced humification and oligomerization of EE2, which obviously alter the geochemical fate and transport of EE2 in natural aquatic ecosystems.

MnO2 nanozyme-driven polymerization and decomposition mechanisms of 17β-estradiol: Influence of humic acid

Nanozymes, which display the bifunctional properties of nanomaterials and natural enzymes, are useful tools for environmental remediation. In this research, nano-MnO₂ was selected for its intrinsic enzyme-like activity to remove 17β-estradiol (E2). Results indicated that nano-MnO₂ exhibited laccase-like activity (7.22 U·mg^-1) and removed 97.3 % of E2 at pH 6. Humic acid (HA) impeded E2 removal (only 72.4 %) by competing with E2 for the catalytic sites of the MnO₂ nanozyme surface, and there was a good linear correlation between the kinetic constants and HA concentrations (R² = 0.9489). Notably, the phenolic -OH of E2 interacted with HA to yield various polymeric products via radical-driven covalent coupling, resulting in ablation of phenolic -OH but increase of ether groups in the polymeric structure. Intermediate products, including estrone, E2 homo-/hetero-oligomers, E2 hydroxylated and quinone-like products, as well as aromatic ring-opening species, were identified. Interestingly, HA hindered the extent of E2 oxidation, homo-coupling, and decomposition but accelerated E2 and HA hetero-coupling. A reasonable catalytic pathway of E2 and HA involving MnO₂ nanozyme was proposed. These findings provide novel insights into the influence of HA on MnO₂ nanozyme-driven E2 radical polymerization and decomposition, consequently favoring the ecological water restoration and the global carbon cycle.

Oxidative Oligomerization of Phenolic Endocrine Disrupting Chemicals Mediated by Mn(III)-L Complexes and the Role of Phenoxyl Radicals in the Enhanced Removal: Experimental and Theoretical Studies

Soluble manganese(III), stabilized by ligands as Mn(III)-L complexes, are ubiquitous in natural waters and wastewaters and can potentially serve as both the oxidant and reductant in one-electron transfer reactions with organic contaminants. In this study, the oxidative transformations of 14 phenolic endocrine disrupting chemicals (EDCs) by in situ-formed Mn(III)-L complexes, generated from irradiated water containing Mn(II) and humic acid, were investigated. The pseudo-first-order rate constants (k_obs, h^-1) of these phenols varied from 1.0 × 10^-4 to 5.9 × 10^-2. A quantitative structure-activity relationship model was developed, which suggests that the electron-donating ability (E_HOMO) of phenolic chemicals was the most important molecular characteristic for the Mn(III)-L-mediated oxidative transformation. Phenol transformation was initiated by the generation of a phenoxyl radical through electron transfer to Mn(III)-L. Subsequent self-coupling reactions between phenoxyl radicals resulted in the formation of self-coupling dimers and trimers. With the addition of simple phenol as a cosubstrate, enhanced transformations of these phenolic EDCs were clearly observed, and cross-coupling products of simple phenol and the substrates were also detected. In addition, a reaction activation energy calculation based on the transition-state theory indicated that the cross-coupling reaction was more likely than the self-coupling reaction to occur in the presence of phenol. This work provides new insights into the environmental fate of phenolic compounds.

Visible light and fulvic acid assisted generation of Mn(III) to oxidize bisphenol A: The effect of tetrabromobisphenol A

Bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), endocrine disrupting compounds (EDCs), are of increasing concerns for many years. This paper presents the elimination of BPA under visible light (VL) (λ ≥ 420 nm) irradiated solutions containing fulvic acid (FA) and MnSO₄ (Mn(II)), and examines the possible effects of TBBPA on the transformation of BPA. After 72 h of reaction time, the removal efficiency of BPA in the studied system was 69%. Results of different experiments to identify oxidative species suggested the dominate role of soluble manganese (III) (Mn(III)) in the conversion of BPA. The transformation of BPA by the VL/FA/Mn(II) system was through self-oligomerization in absence of co-existence of TBBPA. In the co-existence of BPA with TBBPA, the removal of BPA was largely inhibited due to the competition with available Mn(III) and the possible occurrence of cross-coupling reactions between the two EDCs. This phenomenon was further elucidated by product analyses and density functional theory (DFT) calculations. The energy difference (ΔE) for generating a cross-coupling product was calculated as -23.4 kJ mol^-1, much lower than the positive values of ΔE for self-coupling products of BPA or TBBPA, demonstrating that cross-coupling reactions between BPA and TBBPA likely occurred easier than the respective self-coupling reactions. The toxicity test showed that the overall estrogenic activity of BPA reaction solution was significantly decreased by the VL/FA/Mn(II) system. In general, our study provided new insights into the transformation of co-existing EDCs by in situ formed Mn(III) in aqueous solution.

Fungal laccase-mediated humification of estrogens in aquatic ecosystems

Estrogens are a category of non-degradable organic pollutants prevalent in aquatic environments with reported health risks in human and wildlife reproduction. A biotechnological approach is proposed for utilizing fungal laccase-mediated humification reactions (L-MHRs) to remove estrogens from water. Through a reactive radical-mediated C-C, C-O-C, or C-N-C covalent coupling mechanism, multifarious complex polymeric structures are generated having limited solubilities, which significantly reduces their estrogenic activity and ecotoxicity. This review highlights the available literature associated with the self/cross-coupling mechanism of fungal L-MHRs in catalyzing the single-electron oxidation of estrogens and humic acid (HA). Advances in identifying unknown estrogen-HA cross-coupling products using high-resolution mass spectrometry combined with ¹³C-isotope labeling and ¹³C NMR may provide key research directions beneficial to aquatic ecological restoration measures.

Generation of Active Mn(III)aq by a Novel Heterogeneous Electro-permanganate Process with Manganese(II) as Promoter and Stabilizer

Our study on the synergetic effect of electrolysis and permanganate (E-PM) revealed a novel alternative method for generating active Mn(III)_aq heterogeneously by electrochemically activating PM with Mn²⁺ as promoter and stabilizer. We systematically explored the generation mechanism of Mn(III)_aq. It indicated that all three components (electrolysis + PM + Mn²⁺) were necessary to facilitate the generation of active Mn(III) in the E-PM-Mn²⁺ process. It was worth noting that Mn²⁺, as essential promoter and Mn(III)_aq stabilizer, could considerably enhance the concentration of Mn(III) in the E-PM-Mn²⁺ process. Further study revealed that the active Mn(III) was mainly produced on cathode rather than in aqueous solution or on anode. In addition, the soluble Mn(III)_aq generated in the E-PM-Mn²⁺ process was demonstrated to be very efficient for the degradation and mineralization of diclofenac (DCF) as well as methyl blue, carbamazepine, phenol, sulfamethoxazole, and nitrobenzene. Moreover, the effects of the main operating parameters (Mn²⁺ dosage, PM dosage, applied current density, pH of solution, and contaminant concentration) and different water matrices on the E-PM-Mn²⁺ process were investigated systematically. Possible degradation pathways of DCF in the E-PM-Mn²⁺ process were also proposed. The results demonstrated that the E-PM-Mn²⁺ system based on active Mn(III)_aq could create a more efficient, sustainable, and less energy costing technology for water treatment.