The profound review of Fenton process: What's the next step?

Fenton and Fenton-like processes, which could produce highly reactive species to degrade organic contaminants, have been widely used in the field of wastewater treatment. Therein, the chemistry of Fenton process including the nature of active oxidants, the complicated reactions involved, and the behind reason for its strongly pH-dependent performance, is the basis for the application of Fenton and Fenton-like processes in wastewater treatment. Nevertheless, the conflicting views still exist about the mechanism of the Fenton process. For instance, reaching a unanimous consensus on the nature of active oxidants (hydroxyl radical or tetravalent iron) in this process remains challenging. This review comprehensively examined the mechanism of the Fenton process including the debate on the nature of active oxidants, reactions involved in the Fenton process, and the behind reason for the pH-dependent degradation of contaminants in the Fenton process. Then, we summarized several strategies that promote the Fe(II)/Fe(III) cycle, reduce the competitive consumption of active oxidants by side reactions, and replace the Fenton reagent, thus improving the performance of the Fenton process. Furthermore, advances for the future were proposed including the demand for the high-accuracy identification of active oxidants and taking advantages of the characteristic of target contaminants during the degradation of contaminants by the Fenton process.

A review on reactive oxygen species-induced mechanism pathways of pharmaceutical waste degradation: Acetaminophen as a drug waste model.

Innately designed to induce physiological changes, pharmaceuticals are foreknowingly hazardous to the ecosystem. Advanced oxidation processes (AOPs) are recognized as a set of contemporary and highly efficient methods being used as a contrivance for the removal of pharmaceutical residues. Since reactive oxygen species (ROS) are formed in these processes to interact and contribute directly toward the oxidation of target contaminant(s), a profound insight regarding the mechanisms of ROS leading to the degradation of pharmaceuticals is fundamentally significant. The conceptualization of some specific reaction mechanisms allows the design of an effective and safe degradation process that can empirically reduce the environmental impact of the micropollutants. This review mainly deliberates the mechanistic reaction pathways for ROS-mediated degradation of pharmaceuticals often leading to complete mineralization, with a focus on acetaminophen as a drug waste model.

Enhancing microbial superoxide generation and conversion to hydroxyl radicals for enhanced bioremediation using iron-binding ligands.

Harnessing bacteria for superoxide production in bioremediation holds immense promise, yet its practical application is hindered by slow production rates and the relatively weak redox potential of superoxide. This study delves into a cost-effective approach to amplify superoxide production using an Arthrobacter strain, a prevalent soil bacterial genus. Our research reveals that introducing a carbon source along with specific iron-binding ligands, including deferoxamine (DFO), diethylenetriamine pentaacetate (DTPA), citrate, and oxalate, robustly augments microbial superoxide generation. Moreover, our findings suggest that these iron-binding ligands play a pivotal role in converting superoxide into hydroxyl radicals by modulating the electron transfer rate between Fe(III)/Fe(II) and superoxide. Remarkably, among the tested ligands, only DTPA emerges as a potent promoter of this conversion process when complexed with Fe(III). We identify an optimal Fe(III) to DTPA ratio of approximately 1:1 for enhancing hydroxyl radical production within the Arthrobacter culture. This research underscores the efficacy of simultaneously introducing carbon sources and DTPA in facilitating superoxide production and its subsequent conversion to hydroxyl radicals, significantly elevating bioremediation performance. Furthermore, our study reveals that DTPA augments superoxide production in cultures of diverse soils, with various soil microorganisms beyond Arthrobacter identified as contributors to superoxide generation. This emphasizes the universal applicability of DTPA across multiple bacterial genera. In conclusion, our study introduces a promising methodology for enhancing microbial superoxide production and its conversion into hydroxyl radicals. These findings hold substantial implications for the deployment of microbial reactive oxygen species in bioremediation, offering innovative solutions for addressing environmental contamination challenges.

Dihydroquercetin and biochaga reduce H2O2 induced DNA damage in peripheral blood mononuclear cells of obese women in vitro-a pilot study.

Systemic oxidative stress stemming from increased free radical production and reduced antioxidant capacity are common characteristics of obese individuals. Using hydrogen peroxide (H2O2) to induce DNA damage in vitro, in peripheral blood mononuclear cells (PBMCs) from obese subjects and controls, the DNA protective ability of dihidroqercetin (DHQ) and biochaga (B) alone or in combination, were evaluated. The effects of DHQ and B were estimated under two experimental conditions: pre-treatment, where cells were pre-incubated with the substances prior to H2O2 exposure; and post-treatment when cells were first exposed to H2 H2O2, and further treated with the compounds. DNA damage was evaluated using the comet assay. The results of pre- and post-treatment showed a significant decrease in DNA damage produced by H2O2 in the obese group. This decrease was not significant in control group probably due to a small number of subjects in this pilot study. More prominent attenuation was noted in the pre-treatment with DHQ (250 µg/mL). Analysis of antioxidant properties revealed that DHQ's remarkable reducing power, 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, and potent ∙OH scavenging properties may contribute to strong attenuation of H2O2 induced DNA damage. Also, B showed strong reducing power, DPPH, and ∙OH scavenging ability, while reducing power and DPPH scavenger effects were increased in the presence of DHQ. Conclusively, DHQ and B may reduce H2O2-induced DNA damage in PBMCs from obese subjects when challenged in vitro, and could be valuable tools in future research against oxidative damage-related conditions.

Photochemical fate of nonionic polyacrylamide induced by hydroxyl radicals in the natural water: Mineralization mechanism exploration and half-life time evaluation.

Water-soluble polyacrylamide (PAM) compounds have been used extensively in various sectors. The abundance of PAM in the environment raises concerns about its environmental impact. However, the mineralization of PAM in water under natural light irradiation remains insufficiently explored. This study utilizes nonionic PAM (nPAM) as a representative model to investigate both the mechanism and efficiency of nPAM degradation in water when exposed to ultraviolet (UV) light with hydrogen peroxide (H2O2) as the hydroxyl radical source. In the dark or with only UVA irradiation, negligible mineralization of nPAM occurred. In contrast, the presence of hydroxyl radicals (produced by the UVA/H2O2 system) produced 50 % nPAM mineralization over 7 days under our experimental conditions. The corresponding molecular weight (MW) of the nPAM was swiftly reduced from 1.58 ×106 Da to 1.59 ×103 Da in 3 days. Moreover, five carboxylic acids and nitrate ions were identified as the photodegradation intermediates of nPAM. The efficiencies of nPAM photodegradation by the UVA/H2O2 system in different natural waters and environmental conditions were assessed. The rate constant for the reaction between the hydroxyl radical and nPAM was 2.17 ×109 M-unit-1 s-1. The half-lives of nPAM in the sea and continental surface waters were determined to be several years and dozens of days, respectively. The application of UVB obviously accelerated the mineralization of nPAM in ultrapure water (71 % degradation in 7 days). Moreover, mineralization of concentrated nPAM (200 mg/L) in sea water was more efficient when both UVA- and UVB-activated H2O2 were used. Additionally, toxic acrylamide was not generated during nPAM photodegradation. Moreover, the photodegradation intermediates from nPAM were found to be neither acutely nor chronically toxic to aquatic organisms. This comprehensive study sheds light on the photochemical fate of nPAM in natural waters and provides essential insight for practical treatment of PAM in water systems.

Achieving realistic ozonation conditions with synthetic water matrices comprising low-molecular-weight scavenger compounds.

Ozonation is used worldwide for drinking water disinfection and increasingly also for micropollutant abatement from wastewater. Identification of transformation products formed during the ozonation of micropollutants is challenging due to several factors including (i) the reactions of both oxidants, ozone and hydroxyl radicals with the micropollutants, as well as with intermediate transformation products, (ii) effects of the water matrix on the ozone and hydroxyl radical chemistry and (iii) the generation of oxidation by-products. In this study, a simple approach to achieve realistic ozonation conditions in the absence of dissolved organic matter has been developed. It is based on composing synthetic water matrices with low-molecular-weight scavenger compounds (phenol, methanol, acetate, and carbonate) that mimic the chemical interactions of ozone and hydroxyl radicals with real water matrices. Synthetic waters composed of only four low-molecular-weight compounds successfully replicated two lake waters and two secondary wastewater effluents, matching instantaneous ozone demand, ozone and hydroxyl radical exposures in the initial phase, as well as the ozone evolution in the second phase of the ozonation process. The synthetic water matrices also reproduced the effects of temperature and pH changes observed in real waters. The abatement of two micropollutants, bezafibrate and atrazine, and the formation of the corresponding transformation products during ozonation were in agreement for synthetic and real waters. Furthermore, the kinetics and extent of bromate formation during ozonation in synthetic water were comparable to real lake water and wastewater. This supports the robustness of the proposed approach because bromate formation is very sensitive to the interplay of ozone and hydroxyl radicals. Furthermore, with the novel reaction system, a significant effect of hydroxyl radicals scavenging by carbonate on bromate formation was demonstrated. Overall, the herein-developed approach based on synthetic water matrices allows to perform realistic ozonation studies including both oxidants, ozone and hydroxyl radicals, without the constraints of using dissolved organic matter.

Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems.

Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl (•OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). •OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, •OH generation, and ATZ oxidation by •OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca2+, Na+, HCO3-, and SO42-) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.

In situ Production of Hydroxyl Radicals via Three-Electron Oxygen Reduction: Opportunities for Water Treatment.

The electro-Fenton (EF) process is an advanced oxidation technology with significant potential; however, it is limited by two steps: generation and activation of H2O2. In contrast to the production of H2O2 via the electrochemical two-electron oxygen reduction reaction (ORR), the electrochemical three-electron (3e-) ORR can directly activate molecular oxygen to yield the hydroxyl radical (·OH), thus breaking through the conceptual and operational limitations of the traditional EF reaction. Therefore, the 3e- ORR is a vital process for efficiently producing ·OH in situ, thus charting a new path toward the development of green water-treatment technologies. This review summarizes the characteristics and mechanisms of the 3e- ORR, focusing on the basic principles and latest progress in the in situ generation and efficient utilization of ·OH through the modulation of the reaction pathway, shedding light on the rational design of 3e- ORR catalysts, mechanistic exploration, and practical applications for water treatment. Finally, the future developments and challenges of efficient, stable, and large-scale utilization of ·OH are discussed based on achieving optimal 3e- ORR regulation and the potential to combine it with other technologies.

Oxidation and mineralization rates of harmful organic chemicals in hydroxyl radical induced reactions.

In most of advanced oxidation processes (AOPs) used to destroy harmful organic chemicals in water/wastewater hydroxyl radical (•OH) reactions oxidize (increasing the oxygen/carbon ratio in the molecules) and mineralize (transforming them to inorganic molecules, H2O, CO2, etc.) these contaminants. In this paper, we used the radiolysis of water to produce •OH and characterised the rate of oxidation and mineralization by the dose dependences of the Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) content values. Analysis of the dose dependences for 34 harmful organic compounds showed large differences in the oxidation and mineralization rates and these parameters are characteristic to the given group of chemicals. E.g., the rate of oxidation is relatively low for fluoroquinolone antibiotics; it is high for ß-blocker medicines. Mineralization rates are low for both fluoroquinolones and ß-blockers. The one-electron-oxidant •OH in most cases induces two - four-electron-oxidations. Most of the degradation takes place gradually, through several stable molecule intermediates. However, based on the results it is likely, that some part of the oxidation and mineralization takes place parallel. The organic radicals formed in •OH reactions react with several O2 molecules and release several inorganic fragments during the radical life cycle.

Antioxidants are ineffective at quenching reactive oxygen species inside bacteria and should not be used to diagnose oxidative stress.

A wide variety of stresses have been proposed to exert killing effects upon bacteria by stimulating the intracellular formation of reactive oxygen species (ROS). A key part of the supporting evidence has often been the ability of antioxidant compounds to protect the cells. In this study, some of the most-used antioxidants-thiourea, glutathione, N-acetylcysteine, and ascorbate-have been examined. Their ability to quench superoxide and hydrogen peroxide was verified in vitro, but the rate constants were orders of magnitude too slow for them to have an impact upon superoxide and peroxide concentrations in vivo, where these species are already scavenged by highly active enzymes. Indeed, the antioxidants were unable to protect the growth and ROS-sensitive enzymes of E. coli strains experiencing authentic oxidative stress. Similar logic posits that antioxidants cannot substantially quench hydroxyl radicals inside cells, which contain abundant biomolecules that react with them at diffusion-limited rates. Indeed, antioxidants were able to protect cells from DNA damage only if they were applied at concentrations that slow metabolism and growth. This protective effect was apparent even under anoxic conditions, when ROS could not possibly be involved, and it was replicated when growth was similarly slowed by other means. Experimenters should discard the use of antioxidants as a way of detecting intracellular oxidative stress and should revisit conclusions that have been based upon such experiments. The notable exception is that these compounds can effectively degrade hydrogen peroxide from environmental sources before it enters cells.

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.

Reaction mechanism of antioxidant inhibition of hydroxyl radical in coal oxidation.

To solve the problem of unclear targeted inhibition of key free radicals by antioxidants, this paper took the hydroxyl radical with the highest oxidation activity of coal as the inhibition target and selected five antioxidants such as ethylene diamine tetraacetic acid, tea polyphenol, citric acid, vitamin C, and proanthocyanidins. Based on the theory of quantum chemistry, the characteristics and oxidation pathway of antioxidants inhibiting coal oxidation of hydroxyl radical were analyzed. Analyze the influence characteristics of antioxidants on the evolution of free radicals in coal through an electron paramagnetic resonance experiment (ESR). The results showed that the electron density of antioxidants was mainly distributed in the functional groups of carboxyl and hydroxyl, which played a key inhibitory role, and the vicinity of carboxyl and hydroxyl and other functional groups was positive potential, which was the active site of inhibiting hydroxyl radical. The order of inhibitory capacity of the five antioxidants was determined as GTP > PC > EDTA > CA > VC. It is concluded that the energy barrier of hydroxyl radical inhibition by citric acid is much lower than that of EDTA. For the hydrogen extraction reaction, VC inhibited the hydroxyl radical pathway with a higher energy barrier than the other three antioxidants. The mechanism of five antioxidants inhibiting •OH reaction was comprehensively analyzed. It was found that tea polyphenols have more active sites that can react with •OH to quench it, so the inhibition of tea polyphenols should be the most significant. When antioxidants inhibit coal spontaneous combustion, the type, complexity, concentration, and linewidth of free radicals in coal molecules are lower than those in raw coal, with GTP antioxidants having the best inhibitory effect. The research results have important theoretical and practical significance for revealing the mechanism of coal spontaneous combustion inhibition and developing directional coal spontaneous combustion inhibition technology.

Water Vapor Condensation Triggers Simultaneous Oxidation and Hydrolysis of Organic Pollutants on Iron Mineral Surfaces.

Increasing worldwide contamination with organic chemical compounds is a paramount environmental challenge facing humanity. Once they enter nature, pollutants undergo transformative processes that critically shape their environmental impacts and associated risks. This research unveils previously overlooked yet widespread pathways for the transformations of organic pollutants triggered by water vapor condensation, leading to spontaneous oxidation and hydrolysis of organic pollutants. These transformations exhibit variability through either sequential or parallel hydrolysis and oxidation, contingent upon the functional groups within the organic pollutants. For instance, acetylsalicylic acid on the goethite surface underwent sequential hydrolysis and oxidation that first hydrolyzed to salicylic acid followed by hydroxylation oxidation of the benzene moiety driven by the hydroxyl radical (•OH). In contrast, chloramphenicol underwent parallel oxidation and hydrolysis, forming hydroxylated chloramphenicol and 2-amino-1-(4-nitrophenyl)-1,3-propanediol, respectively. The spontaneous oxidation and hydrolysis occurred consistently on three naturally abundant iron minerals with the key factors being •OH production capacity and surface binding strength. Given the widespread presence of iron minerals on Earth's surface, these spontaneous transformation paths could play a role in the fate and risks of organic pollutants of health concerns.

Higher efficiency of vanadate iron in heterogeneous Fenton-like systems to pretreat sugarcane bagasse and its enzymatic saccharification.

Pretreatment is crucial for effective enzymatic saccharification of lignocellulose such as sugarcane bagasse (SCB). In the present study, SCB was pretreated with five kinds of heterogeneous Fenton-like systems (HFSs), respectively, in which α-FeOOH, α-Fe2O3, Fe3O4, and FeS2 worked as four traditional heterogeneous Fenton-like catalysts (HFCs), while FeVO4 worked as a novel HFC. The enzymatic reducing sugar conversion rate was then compared among SCB after different heterogeneous Fenton-like pretreatments (HFPs), and the optimal HFS and pretreatment conditions were determined. The mechanism underlying the difference in saccharification efficiency was elucidated by analyzing the composition and morphology of SCB. Moreover, the ion dissolution characteristics, variation of pH and Eh values, H2O2 and hydroxyl radical (·OH) concentration of FeVO4 and α-Fe2O3 HFSs were compared. The results revealed that the sugar conversion rate of SCB pretreated with FeVO4 HFS reached up to 58.25%, which was obviously higher than that under other HFPs. In addition, the surface morphology and composition of the pretreated SCB with FeVO4 HFS were more conducive to enzymatic saccharification. Compared with α-Fe2O3, FeVO4 could utilize H2O2 more efficiently, since the dissolved Fe3+ and V5+ can both react with H2O2 to produce more ·OH, resulting in a higher hemicellulose and lignin removal rate and a higher enzymatic sugar conversion rate. It can be concluded that FeVO4 HFP is a promising approach for lignocellulose pretreatment.

Reduced greenhouse gas emission by reactive oxygen species during composting.

Reactive oxygen species (ROS) is produced in the composting, which effectively promote organic matter transformation and humification process, but the effect of ROS on greenhouse gas emissions in this process has not been understood. This study proposed and validated that ROS can effectively reduce greenhouse gas emissions intheprocessofcomposting. Compared with ordinary thermophilic composting (oTC), thermophilic composting (imTC) that was supplemented by iron mineral increased ROS production by 1.38 times, and significantly reduced greenhouse gas emissions by 45.12%. Microbial community analysis showed no significant difference in the abundance of microbes involved in greenhouse gas production between oTC and imTC. Further correlation analysis proved that ROS played a crucial role in influencing greenhouse gas emissions throughout the composting process, especially in the initial phase. These findings provide new strategies for managing livestock and poultry manure to mitigate climate change.

Kinetics and mechanism of the gas-phase reaction of the hydroxyl radical with meta-aminotoluene compound.

CONTEXT: An ab initio investigation into the potential energy landscape of the meta-aminotoluene + •OH reaction has been conducted in this study. The calculated results reveal that the reaction channel leading to the product (NHC6H4CH3 + H2O) prevails under the 300-1700 K temperature range, while the reaction path forming the product (NH2C6H4CH2 + H2O) dominates in the higher-temperature region (T ≥ 1800 K). Within the specified temperature range, the product branching ratio for the former declines from 48 to 30%, while the latter shows an increase, reaching 29%. The overall second-order rate constants of the titled reaction obtained at the pressure 760 Torr (N2) can be illustrated by the modified Arrhenius expression of ktotal = 1.46 × 10-13 T0.58 exp[(-0.759 kcal.mol-1)/RT] cm3 molecule-1 s-1 and ktotal = 1.86 × 10-22 T3.24 exp[(-5.086 kcal.mol-1)/RT] cm3 molecule-1 s-1, covering the temperature range of T = 300-600 K and T > 600 K, respectively. The total rate constant at the ambient conditions in this work, 1.43 × 10-11 cm3 molecule-1 s-1, has been found to be roughly one order of magnitude lower than the available experimental data, ~ 1.2 × 10-10 cm3 molecule-1 s-1, measured by Atkinson et al., Rinke et al., and Witte et al., or the theoretical value, 4.4 × 10-10 cm3 molecule-1 s-1, and calculated by Abdel-Rahman and co-workers for the aniline + •OH reaction. METHODS: The structures of reactants, transition states, intermediate states, and products of the meta-aminotoluene + •OH reaction are calculated with the aug-cc-pVTZ basis set and the methods DFT/B3LYP and CCSD(T). The rate constants and branching ratios in the 300-2000 K temperature range are calculated with the statistical theoretical TST and RRKM master equation computations including tunneling corrections, with potential energy surface constructed by the CCSD(T)//B3LYP/aug-cc-pVTZ approach.

A review on recent advancements in the treatment of polyaromatic hydrocarbons (PAHs) using sulfate radicals based advanced oxidation process.

Polyaromatic hydrocarbons (PAHs) are the most persistent compounds that get contaminated in the soil and water. Nearly 16 PAHs was considered to be a very toxic according US protection Agency. Though its concentration level is low in the environments but the effects due to it, is enormous. Advanced Oxidation Process (AOP) is an emergent methodology towards treating such pollutants with low and high molecular weight of complex substances. In this study, sulfate radical (SO4‾•) based AOP is emphasized for purging PAH from different sources. This review essentially concentrated on the mechanism of SO4‾• for the remediation of pollutants from different sources and the effects caused due to these pollutants in the environment was reduced by this mechanism is revealed in this review. It also talks about the SO4‾• precursors like Peroxymonosulfate (PMS) and Persulfate (PS) and their active participation in treating the different sources of toxic pollutants. Though PS and PMS is used for removing different contaminants, the degradation of PAH due to SO4‾• was presented particularly. The hydroxyl radical (•OH) mechanism-based methods are also emphasized in this review along with their limitations. In addition to that, different activation methods of PS and PMS were discussed which highlighted the performance of transition metals in activation. Also this review opened up about the degradation efficiency of contaminants, which was mostly higher than 90% where transition metals were used for activation. Especially, on usage of nanoparticles even 100% of degradation could be able to achieve was clearly showed in this literature study. This study mainly proposed the treatment of PAH present in the soil and water using SO4‾• with different activation methodologies. Particularly, it emphasized about the importance of treating the PAH to overcome the risk associated with the environment and humans due to its contamination.

Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification.

Carbon-based single-atom catalysts (SACs) have been gradually introduced in heterogeneous catalytic ozonation (HCO), but the interface mechanism of O3 activation on the catalyst surface is still ambiguous, especially the effect of a surface hydroxyl group (M-OH) at metal sites. Herein, we combined theoretical calculations with experimental verifications to comprehensively investigate the O3 activation mechanisms on a series of conventional SAC structures with N-doped nanocarbon substrates (MN4-NCs, where M = Mn, Fe, Co, Ni). The synergetic manipulation effect of the metal atom and M-OH on O3 activation pathways was paid particular attention. O3 tends to directly interact with the metal atom on MnN4-NC, FeN4-NC, and NiN4-NC catalysts, among which MnN4-NC has the best catalytic activity for its relatively lower activation energy barrier of O3 (0.62 eV) and more active surface-adsorbed oxygen species (Oads). On the CoN4-NC catalyst, direct interaction of O3 with the metal site is energetically infeasible, but O3 can be activated to generate Oads or HO2 species from direct or indirect participation of M-OH sites. The experimental results showed that 90.7 and 82.3% of total organic carbon (TOC) was removed within 40 min during catalytic ozonation of p-hydroxybenzoic acid with MnN4-NC and CoN4-NC catalysts, respectively. Phosphate quenching, catalyst characterization, and EPR measurement further supported the theoretical prediction. This contribution provides fundamental insights into the O3 activation mechanism on SACs, and the methods and ideals could be helpful for future studies of environmental catalysis.

Critical Role of Mineral Fe(IV) Formation in Low Hydroxyl Radical Yields during Fe(II)-Bearing Clay Mineral Oxygenation.

In subsurface environments, Fe(II)-bearing clay minerals can serve as crucial electron sources for O2 activation, leading to the sequential production of O2•-, H2O2, and •OH. However, the observed •OH yields are notably low, and the underlying mechanism remains unclear. In this study, we investigated the production of oxidants from oxygenation of reduced Fe-rich nontronite NAu-2 and Fe-poor montmorillonite SWy-3. Our results indicated that the •OH yields are dependent on mineral Fe(II) species, with edge-surface Fe(II) exhibiting significantly lower •OH yields compared to those of interior Fe(II). Evidence from in situ Raman and Mössbauer spectra and chemical probe experiments substantiated the formation of structural Fe(IV). Modeling results elucidate that the pathways of Fe(IV) and •OH formation respectively consume 85.9-97.0 and 14.1-3.0% of electrons for H2O2 decomposition during oxygenation, with the Fe(II)edge/Fe(II)total ratio varying from 10 to 90%. Consequently, these findings provide novel insights into the low •OH yields of different Fe(II)-bearing clay minerals. Since Fe(IV) can selectively degrade contaminants (e.g., phenol), the generation of mineral Fe(IV) and •OH should be taken into consideration carefully when assessing the natural attenuation of contaminants in redox-fluctuating environments.

Effects of chemical composition of ambient PM2.5 measured in Seoul on potential health risks and generation of reactive oxygen species.

This study assesses the health effects associated with the chemical species of ambient particulate matter (PM) with an aerodynamic diameter ≤2.5 µm (PM2.5) in Seoul, focusing on identifying key chemical constituents and their sources. We employed two approaches to estimate health risks: (1) evaluating carcinogenic and noncarcinogenic risks using IRIS (Integrated Risk Information System) data from the US EPA (Environmental Protection Agency), and (2) quantifying the generation of hydroxyl radicals (·OH) following exposure to PM2.5 in surrogate lung fluid (SLF). Our results show a significant impact on human health from certain elements (Cr, Ni, As, and Cd) and polycyclic aromatic hydrocarbons (PAHs) (DaeP, DahA, and BaP for carcinogenic risks; BaP and BeP for noncarcinogenic risks). Notably, Cr and BaP, which are influential in both risk assessment and ·OH generation, highlight their significant roles in human health impacts. However, other components (e.g., CPP, BaP, BghiP, BaA, CHR, PYR, FLT, Ca, Mg, and Cu), though contributors to ·OH generation, were not included in the EPA's health risk assessment, suggesting a need for a broader PM2.5 compositional analysis to more accurately determine exposure concentrations and assess inhalation risks. These components predominantly originate from anthropogenic sources, such as combustion, vehicles, and industrial activities, underscoring the significant health implications of the pollutants emitted from these sources. The study concluded that focusing solely on the mass reduction of PM2.5 may not suffice; a dual approach that reduces both mass concentration and chemical-specific health risks is imperative for effective public health protection.