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To oxidize trace concentrations of organic contaminants under conditions relevant to surface- and groundwater, air-diffusion cathodes were coupled to stainless-steel cathodes that convert atmospheric O2 into hydrogen peroxide (H2O2), which then was activated to produce hydroxyl radicals (·OH). By separating H2O2 generation from its activation and employing a flow-through electrode consisting of stainless-steel fibers, the two processes could be operated efficiently in a manner that overcame mass-transfer limitations for O2, H2O2, and trace organic contaminants. The flexibility resulting from separate control of the two processes made it possible to avoid both the accumulation of excess H2O2 and the energy losses that take place after H2O2 has been depleted. The decrease in treatment efficacy occurring in the presence of natural organic matter was substantially lower than that typically observed in homogeneous advanced oxidation processes. Experiments conducted with ionized and neutral compounds indicated that electrostatic repulsion prevented negatively charged ·OH scavengers from interfering with the oxidation of neutral contaminants. Energy consumption by the dual-cathode system was lower than values reported for other technologies intended for small-scale drinking water treatment systems. The coordinated operation of these two cathodes has the potential to provide a practical, inexpensive way for point-of-use drinking water treatment.

Organic molecules in the environment oxidatively degrade by a variety of free radical, microbial, and biogeochemical pathways. A significant pathway is heterogeneous autoxidation, in which degradation occurs via a network of carbon and oxygen centered free radicals. Recently, we found evidence for a new heterogeneous autoxidation mechanism of squalene that is initiated by hydroxyl (OH) radical addition to a carbon-carbon double bond and apparently propagated through pathways involving Criegee Intermediates (CI) produced from β-hydroxy peroxy radicals (β-OH-RO2•). It remains unclear, however, exactly how CI are formed from β-OH-RO2•, which could occur by a unimolecular or bimolecular pathway. Combining kinetic models and multiphase OH oxidation measurements of squalene, we evaluate the kinetic viability of three mechanistic scenarios. Scenario 1 assumes that CI are formed by the unimolecular bond scission of β-OH-RO2•, whereas Scenarios 2 and 3 test bimolecular pathways of β-OH-RO2• to yield CI. Scenario 1 best replicates the entire experimental data set, which includes effective uptake coefficients vs [OH] as well as the formation kinetics of the major products (i.e., aldehydes and secondary ozonides). Although the unimolecular pathway appears to be kinetically viable, future high-level theory is needed to fully explain the mechanistic relationship between CI and β-OH-RO2• in the condensed phase.

The reaction of peracetic acid (PAA) and Fe(II) has recently gained attention due to its utility in wastewater treatment and its role in cloud chemistry. Aerosol-cloud interactions, partly mediated by aqueous hydroxyl radical (OH) chemistry, represent one of the largest uncertainties in the climate system. Ambiguities remain regarding the sources of OH in the cloud droplets. Our research group recently proposed that the dark and light-driven reaction of Fe(II) with peracids may be a key contributor to OH formation, producing a large burst of OH when aerosol particles take up water as they grow to become cloud droplets, in which reactants are consumed within 2 min. In this work, we quantify the OH production from the reaction of Fe(II) and PAA across a range of physical and chemical conditions. We show a strong dependence of OH formation on ultraviolet (UV) wavelength, with maximum OH formation at λ = 304 ± 5 nm, and demonstrate that the OH burst phenomenon is unique to Fe(II) and peracids. Using kinetics modeling and density functional theory calculations, we suggest the reaction proceeds through the formation of an [Fe(II)-(PAA)2(H2O)2] complex, followed by the formation of a Fe(IV) complex, which can also be photoactivated to produce additional OH. Determining the characteristics of OH production from this reaction advances our knowledge of the sources of OH in cloudwater and provides a framework to optimize this reaction for OH output for wastewater treatment purposes.

The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radicals (HO•) from the heat activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C-H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs. In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radicals (SO4-•), to extend the capability of the TOP assay. We examined the oxidation of Nafion-related ether sulfonates that contain C-H or -COO-, characterized the oxidation products, and quantified the F atom balance. The SO4-• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps, such as HF elimination and ester hydrolysis. We further compared the oxidation of legacy fluorotelomers using SO4-• versus HO•. The results suggest novel product distribution patterns, depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100000- or 10000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor. Therefore, (1) the combined use of SO4-• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4-• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants.

Background: White rot fungi produce various reactive oxygen species and ligninolytic enzymes for lignocellulose deconstruction. However, their interactions during the deconstruction of lignocellulosic structural barriers for efficient enzymatic saccharification remain unclear. Results: Herein, the extracellular enzyme activities and secretomic analysis revealed the sequential expression of hydroxyl radical (⋅OH) and manganese peroxidases (MnPs) for lignocellulose deconstruction by the white rot fungus Irpex lacteus. Subsequently, in vitro functional studies found that ⋅OH possessed the ability to disrupt the smooth surface structure of corn stover, resulting in increased enzymatic saccharification and cellulose accessibility. Purified recombinant MnPs from I. lacteus were able to cleave the β-O-4 bond in phenolic and non-phenolic lignin model dimers without the help of any mediators. Furthermore, the sequential pretreatment of corn stover with ⋅OH and MnP exhibited significant synergistic effects, increasing enzymatic saccharification and cellulose accessibility by 2.9-fold and 1.8-fold, respectively. Conclusions: These results proved for the first time the synergistic effects of ⋅OH and MnP pretreatment in improving the enzymatic saccharification and cellulose accessibility of corn stover. These findings also demonstrated the potential application of ⋅OH and MnP pretreatment for the efficient enzymatic saccharification of corn stover. [ABSTRACT FROM AUTHOR]

Heterogeneous Fenton catalysis offers a promising alternative to traditional Fenton oxidation for water treatment as its wider operating pH range and high cyclic performance. However, designing catalysts that can activate H2O2 both actively and selectively to mineralize refractory pollutants remains challenging. Here, a state‐of‐the‐art design principle of constructing spatially separated Fe‐M (M denotes an oxophilic first‐row transition metal) dual single‐atom sites is developed for Fenton‐like catalysis. This strategy enables accelerated redox cycles between the dual metal centers, leading to precise manipulation of Fe···O‐O···M intermediate in H2O2 activation. This, in turn, aids the homolytic decomposition of H2O2 toward selective and efficient •OH generation. Taking Fe‐Cu pairs as an example, the constructed dual sites outperform the individual Fe or Cu sites, demonstrating a higher activation selectivity (94%) for •OH production. Further benefitting from the electronic communications between Fe (electron acceptor) and Cu (electron donor), the SA‐Fe‐Cu‐CN catalyst exhibited an effective H2O2 decomposition with 0.94 mm of •OH yielded within 50 min. Compared to the typical homogeneous system, the SA‐Fe‐Cu‐CN/H2O2 system has higher mineralization capacities toward refractory pollutants and greater pH tolerance. The work provides a new strategy for the design of robust catalysts by creating spatially separated dual single‐atom sites toward multi‐reactant systems. [ABSTRACT FROM AUTHOR]

Flooding and drainage of paddy fields can induce the activation of soil cadmium (Cd)/arsenic (As), which will accumulate in rice grains and threaten human health. Mn oxides influence soil Cd and As availability, but few detailed studies have been reported on how Mn redox simultaneously affects Cd and As mobility during flooding and drainage. Two paddy soils with various Mn contents were incubated under three redox conditions, namely 30-d reduction, 30-d oxidation and 20-d reduction subsequent with 10-d oxidation, to investigate Cd and As migration. During reduction, the soil abundant in native Mn oxides possessed more high-valence Mn oxides, which promoted As oxidation and retarded the reductive dissolution of Fe (oxyhydro)oxides, thereby decreasing As mobility. Cd mobility mainly depended on the conversion between Fe-Mn oxides-bound Cd and exchangeable Cd. The high Mn content was conducive to decreasing Cd mobilization. Furthermore, the oxidation of As in soils was linked with a Fenton-like effect. The generated hydroxyl radicals (•OH) decreased with oxidation and the oxidation of Mn(II) by •OH inhibited As migration but promoted Cd activation. In summary, the mobility of Cd and As was lower in Mn rich soils, which may involve the immobilization, oxidation and catalytic effects of Mn oxides. HIGHLIGHTS: Cd mobility mainly relied on the conversion between Fe-Mn oxides-bound Cd and exchangeable Cd. The redox dependence of Mn played a key role in controlling Cd and As migration in paddy soils. Soils containing higher content of Mn oxides possessed lower mobility of Cd and As. The oxidative effect of •OH on Mn(II) inhibited As mobility but promoted Cd activation. [ABSTRACT FROM AUTHOR]

Using two-color planar laser-induced fluorescence (PLIF) of OH hydroxyl radicals excited at two wavelengths and coherent anti-Stokes Raman scattering (CARS) spectroscopy of H2 molecules in a laboratory burner, we have measured spatial temperature distributions in the central section of a stationary atmospheric laminar flame of a methane–air mixture with partial preliminary mixing of the components. The results of a comparative analysis of the data on two-dimensional PLIF and point CARS thermometry of a spatially inhomogeneous flame are presented, and possibilities of complementary application of these methods for diagnostics are shown. [ABSTRACT FROM AUTHOR]

Increased intramitochondrial free iron is a key feature of various liver diseases, leading to oxidative stress, mitochondrial dysfunction, and liver damage. Polydatin is a polyphenol with a hepatoprotective effect, which has been attributed to its ability to enhance mitochondrial oxidative metabolism and antioxidant defenses, thereby inhibiting reactive oxygen species (ROS) dependent cellular damage processes and liver diseases. However, it has not been explored whether polydatin is able to exert its effects by protecting the phospholipid cardiolipin against damage from excess iron. Cardiolipin maintains the integrity and function of electron transport chain (ETC) complexes and keeps cytochrome c bound to mitochondria, avoiding uncontrolled apoptosis. Therefore, the effect of polydatin on oxidative lipid damage, ETC activity, cytochrome levels, and ROS production was explored in iron-exposed rat liver mitochondria. Fe2+ increased lipid peroxidation, decreased cardiolipin and cytochromes c + c1 and aa3 levels, inhibited ETC complex activities, and dramatically increased ROS production. Preincubation with polydatin prevented all these effects to a variable degree. These results suggest that the hepatoprotective mechanism of polydatin involves the attenuation of free radical production by iron, which enhances cardiolipin levels by counteracting membrane lipid peroxidation. This prevents the loss of cytochromes, improves ETC function, and decreases mitochondrial ROS production. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As antibiotics including the Sulfa drugs (SDs) have been found in aquatic environments, their derivatives and structural analogs have attracted increasing concern as pollutants. In this study, the density functional theory (DFT) and B3LYP method to investigate the direct and indirect photo-decomposition mechanisms of Sulfachloropyridazine (SC) a representative of SDs. The direct Photo-decomposition mechanisms were investigated with two pathways. In the initiation step an intermediate product (IP) was obtained with the computed activation energy (Ea), equal to 4.598 kcal.mol-1. The IP further leaded the path–I and path–II, in which two different products were obtained along with the SO2 as common product. However, the path–I was observed as the main pathway due to its low Ea value and influences of two metal ions (Mg2+ and Na+) on this pathway were investigated. Both the metal ions promoted direct-photo-decomposition of the SC by decreasing Ea the main pathway. Further, the role of •OH radical on the decomposition of the SC was investigated as the indirect photo-decomposition of the SC with three different decomposition schemes. A variety of decomposed products of the SC were obtained in the three schemes with different energy pathways and their calculated activation energies were detected in the range of 2.311 to 18.306, 0.6 to 16.43, and 0.037 to 23.177 Kcal.mol-1 respectively. [ABSTRACT FROM AUTHOR]

Strongly oxidizing ·OH can non‐selectively degrade various organic pollutants, but how to selectively generate ·OH is a great challenge. In this study, the directed generation of ·OH was achieved based on Ni–Ca metastable–nonmetastable bimetallic sites, Ni2+/Ni3+ valence cycling provided electrons for ·OH generation induced by the non‐variable Ca‐based sites, which constructed a nearly 100% selective generation pathway of ·OH (O3 → HO3/HO2 → OH). The antibiotic pefloxacin could be completely removed in 15 min, and the COD removal efficiency for other hard‐to‐degrade pollutants such as oxalic acid and chlorobenzoic acid could reach more than 90%. Ni doping significantly increased the oxygen vacancy and Lewis acid content, and DFT calculations showed that Ni–Ca dual‐site had a lower reaction energy barrier and the complexed hydroxyl radical intermediate *OO had a higher spin density (−0.6), which was more favorable for the generation of ·OH. Therefore, this study provides new ideas for efficient treatment of actual wastewater. [ABSTRACT FROM AUTHOR]

The hydroxyl radical (⋅OH), widely recognized as the most potent free radical, plays a crucial role in numerous physiological and pathological pathways due to its strong oxidizability.Ferroptosis, as a novel mode of cell death, is initiated by the accumulation of iron‐dependent lipid peroxidation. Among them, ⋅OH as the original reactive oxygen species (ROSs)is mass‐produced due to Fenton reaction in vivo and closely related to cancer treatment.Besides, endoplasmic reticulum (ER) as a membrane‐rich structure organelle, is a crucial organelle in all eukaryotes where excessive expression of ROSs, including ⋅OH can triggerER stress which was reported thatwasclosely related toferroptosis. So developing a new probe for their interrelationship research is important. In this paper, we constructed a1,8‐naphthalimide‐based ER‐targeted fluorescence probe named M‐1 to monitor ⋅OH variation in vitro and vivo. What's more, we achieved the monitor of ⋅OH during ER stress andferroptosis processesin cancer cells, andfurther explored the important role of ER stress and ferroptosis processes in SF (sorafenib) involved cancer cells. [ABSTRACT FROM AUTHOR]

Homogenous advanced oxidation processes (AOPs) based on transition metal catalysts toward the activation of H2O2 to hydroxyl radical (•OH) have been widely applied to organic pollutants removal, such as Fenton and Fenton-like processes. These transition metal catalysts mostly flocculate as the pH increases. It's worth noting that the formed transition metal flocs are complex heterogeneous aggregations with active substances, providing diverse reaction spaces and interfaces. However, it is a challenge to distinguish the roles of transition metal flocs in the organic pollutants removal from homogeneous catalytic reactions. Herein, we unveiled a pathway for the long-lasting removal of organic pollutants via Cr flocs adsorbed with •OH (HO•-Cr flocs) using a stepwise method. First, adsorbed •OH (•OHads) within the HO•-Cr flocs was proved to be the active site forming hydrogen bond (H-bond) and van der Waals force with organic pollutants. Then, the presence of switchable electron transfer between Cr and OH groups within the HO•-Cr flocs was revealed, contributing to the persistent existence of •OHads and consequently ensuring the long-lasting organics removal. Further, this removal pathway of organic pollutants was confirmed during the leather wastewater treatment. These findings will complement a different pathway for organic pollutants removal via transition metal flocs and extend the lifetime of homogeneous AOPs based on transition metal catalysts, providing significant implications for their design and optimization. [ABSTRACT FROM AUTHOR]

The removal kinetics of an aqueous mixture of thirteen antibiotics (i.e., ampicillin, cefuroxime, ciprofloxacin, flumequine, metronidazole, ofloxacin, oxytetracycline, sulfadimethoxine, sulfamethoxazole, sulfamethazine, tetracycline, trimethoprim and tylosin) by batch UVC and UVC/H2O2 processes has been modeled in this work. First, molar absorption coefficients (ε), direct quantum yields (Φ) and the rate constants of the reaction of antibiotics with hydroxyl radical (kHO•) (model inputs) were determined for each antibiotic and compared with literature data. The values of these parameters range from 0.3 to 21.8 mM−1 cm−1 for ε, < 0.01 to 67.8 mmol·E−1 for Φ and 3.8 × 109 to 1.7 × 1010 M−1 s−1 for kHO•. Second, a regression model was developed to compute the rate constants of the reactions of the antibiotics with singlet oxygen (k1O₂) from experimental data obtained in batch UVC experiments treating a mixture of the antibiotics. k1O₂ values in the 1–50 × 106 M−1 s−1 range were obtained for the antibiotics studied. Finally, a semi-empirical kinetic model comprising a set of ordinary differential equations was solved to simulate the evolution of the residual concentration of antibiotics and hydrogen peroxide (model outputs) in a completely mixed batch photoreactor. Model predictions were reasonably consistent with the experimental data. The kinetic model developed might be combined with computational fluid dynamics to predict process performance and energy consumption in UVC and UVC/H2O2 applications at full scale. [ABSTRACT FROM AUTHOR]

Spontaneous ionization/breakup of water at the surface of aqueous droplets has been reported with evidence ranging from formation of hydrogen peroxide and hydroxyl radicals, indicated by ions at m/z 36 attributed to OH⋅‐H3O+ or (H2O‐OH2)+⋅ as well as oxidation products of radical scavengers in mass spectra of water droplets formed by pneumatic nebulization. Here, aqueous droplets are formed both by nanoelectrospray, which produces highly charged nanodrops with initial diameters ~100 nm, and a vibrating mesh nebulizer, which produces 2–20 μm droplets that are initially less highly charged. The lifetimes of these droplets range from 10s of μs to 560 ms and the surface‐to‐volume ratios span ~100‐fold range. No ions at m/z 36 are detected with pure water, nor are significant oxidation products for the two radical scavengers that were previously reported to be formed in high abundance. These and other results indicate that prior conclusions about spontaneous hydroxyl radical formation in unactivated water droplets are not supported by the evidence and that water appears to be stable at droplet surfaces over a wide range of droplet size, charge and lifetime. [ABSTRACT FROM AUTHOR]

Citrinin (CIT), a mycotoxin produced by Monascus, Penicillium, and other fungies, can contaminate red yeast rice and other foods, thus constraining their application and development. Exploring efficient degradation methods of citrinin is becoming as one of the hot research topics. In this study, the degradation of citrinin, irradiated by visible (Vis) light, ultraviolet (UV) light, and simulated sunlight alone, as well as in combination with hydrogen peroxide (light/H2O2), was investigated. The research demonstrates UV, Vis, and simulated sunlight all have a degree of degradation on citrinin, and the degradation efficiency correlates with light source and light intensity. Interestingly, when combined with 100 W Vis and 0.01 M H2O2, the citrinin degradation rate increases to 32%, compared to 1% and 5% achieved by Vis and H2O2 alone. Hydroxyl radicals, arising from the uniform cracking of H2O2 under Vis, were experimentally validated by electron spin resonance measurement and could accelerate the dissociation of citrinin by nucleophilic attacking. Employing the density functional theory, we deduced nucleophilic •OH mainly attack onto C8 and C5 site by comparing the electrophilic Parr functions (Pk+) value of main C atom of citrinin. This research presents a rapid and efficient degradation of citrinin by combining visible light with H2O2. Practical Application: This research presents a rapid and efficient method for the degradation of citrnin in red yeast rice and other citrnin containing products by combining visible light with H2O2. [ABSTRACT FROM AUTHOR]

Water from Madín Dam in Mexico has been shown to contain a wide variety of pollutants such as drugs, pesticides, personal care products and compounds that are released into the environment as waste from production processes. In this work, the effect of the main process variables on the percentage of total organic carbon (TOC) removal in water samples from the Madín reservoir was studied by applying a photo-Fenton treatment catalyzed with iron-pillared clays. The catalyst was characterized by XRD, N2 physisorption, DRS and XPS. The sampling and characterization of the water from the Madín reservoir was carried out according to Mexican standards. The system for treatment tests was 0.1 L of reaction volume and a controlled temperature of 23–25 °C, and the reaction system was kept under constant stirring. After 4 h of treatment time under UV light, the TOC removal was 90%, and it was 60% under Vis light. The main ROS involved in the photo-Fenton process driven by UVC light were hydroxyl radicals, while hydroperoxyl radicals predominate in the Vis-light-driven process. Evidence of superoxide anion participation was not found. The toxicity of untreated and treated water was assessed on Danio rerio specimens, and it was observed to be reduced after the photo-Fenton treatment. [ABSTRACT FROM AUTHOR]

Tylosin tartrate, a macrolide antibiotic, is one of a class of emerging contaminants that have been detected in natural bodies of water since they are not easily removed by conventional treatment processes. In this study, the direct and indirect photodegradation of tylosin tartrate was analyzed to understand the role of reactive oxygen species and organic matter that may be present in surface waters. While direct photolysis caused negligible degradation (k = (9.4 ± 1.8) × 10−5 s−1), the addition of 0.4 M hydrogen peroxide (k = (2.18 ± 0.01) × 10−4 s−1) or usage of the photo-Fenton process (k = (2.96 ± 0.02) × 10−4 s−1) resulted in greater degradation. The degradation was maximized by combining tylosin tartrate with an experimentally determined optimal concentration of humic acid (15 mg/L), which readily produced singlet oxygen and increased the overall degradation (k = 1.31 ± 0.05) × 10−3 s−1) by means of indirect photolysis. Absolute pseudo-first-order bimolecular reaction rate constants for tylosin tartrate were measured with singlet oxygen [(4.7936 ± 0.0001) × 105 M−1 s−1] and hydroxyl radical [(5.2693 ± 0.0002) × 109 M−1 s−1] using competition kinetics, and when combined with data on concentration of the reactive oxygen species, showed that the hydroxyl radical makes a contribution to the degradation that is approximately eleven orders of magnitude greater than singlet oxygen. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

BACKGROUND: Hydroxyl radical‐mediated materials primarily liberate more reactive and acutely lethal hydroxyl radical (•OH) and act as potent bactericidal antibiotics, for example H2O2. Hydroxyl radical possess higher tendency than that of H2O2 to attack various biological molecules such as DNA, proteins and iron–sulfur clusters, and impair their proper functioning, actively leading to strongly potent bactericidal effect. To acquire the desired antimicrobial effect, high concentration of H2O2 is required that has found medically harmful to healthy tissues of humans. RESULTS: We herein report framework nucleic acid‐regulated DNAzyme cluster (FDC) – that is, peroxidase‐like hemin‐bound G‐quadruplex (G4/H) DNAzyme – to amplify the catalytic reduction potential of G4/H complex, leading to high conversion rate of H2O2 to more reactive hydroxyl radical that potentially shows the same antibacterial efficiency at lower and safer H2O2 concentration. Specifically, we have grafted multiple copies of DNAzymes outside framework nucleic acid (FNA) to successively achieve 3–9 orders of magnitude enhancement in catalytic activity and antibacterial efficiency of FDC. CONCLUSION: Our designed FDC has successfully alleviated H2O2 toxicity and increased its efficiency as antibacterial material, as FDC amplified the catalytic reduction potential of G4/H DNAzyme, leading to high conversion rate of H2O2 to more reactive •OH that potentially shows the same antibacterial efficiency at lower and safer H2O2 concentration. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

IntroductionOxidative stress mediated by reactive oxygen species (ROS) is a key process for adverse aerosol health effects. Secondary organic aerosols (SOA) account for a major fraction of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5). PM2.5 inhalation and deposition into the respiratory tract causes the formation of ROS by chemical reactions and phagocytosis of macrophages in the epithelial lining fluid (ELF), but their relative contributions are not well quantified and their link to oxidative stress remains uncertain. The specific aims of this project were (1) elucidating the chemical mechanism and quantifying the formation kinetics of ROS in the ELF by SOA; (2) quantifying the relative importance of ROS formation by chemical reactions and macrophages in the ELF.MethodsSOA particles were generated using reaction chambers from oxidation of various precursors including isoprene, terpenes, and aromatic compounds with or without nitrogen oxides (NOx). We collected size-segregated PM at two highway sites in Anaheim, CA, and Long Beach, CA, and at an urban site in Irvine, CA, during two wildfire events. The collected particles were extracted into water or surrogate ELF that contained lung antioxidants. ROS generation was quantified using electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique. PM oxidative potential (OP) was also quantified using the dithiothreitol assay. In addition, kinetic modeling was applied for analysis and interpretation of experimental data. Finally, we quantified cellular superoxide release by RAW264.7 macrophage cells upon exposure to quinones and isoprene SOA using a chemiluminescence assay as calibrated with an EPR spin-probing technique. We also applied cellular imaging techniques to study the cellular mechanism of superoxide release and oxidative damage on cell membranes.ResultsSuperoxide radicals (·O2-) were formed from aqueous reactions of biogenic SOA generated by hydroxy radical (·OH) photooxidation of isoprene, β-pinene, α-terpineol, and d-limonene. The temporal evolution of ·OH and ·O2- formation was elucidated by kinetic modeling with a cascade of aqueous reactions, including the decomposition of organic hydroperoxides (ROOH), ·OH oxidation of primary or secondary alcohols, and unimolecular decomposition of α-hydroxyperoxyl radicals. Relative yields of various types of ROS reflected the relative abundance of ROOH and alcohols contained in SOA, which generated under high NOx conditions, exhibited lower ROS yields. ROS formation by SOA was also affected by pH. Isoprene SOA had higher ·OH and organic radical yields at neutral than at acidic pH. At low pH ·O2- was the dominant species generated by all types of SOA. At neutral pH, α-terpineol SOA exhibited a substantial yield of carbon-centered organic radicals (R·), while no radical formation was observed by aromatic SOA.Organic radicals in the ELF were formed by mixtures of Fe2+ and SOA generated from photooxidation of isoprene, α-terpineol, and toluene. The molar yields of organic radicals by SOA were 5-10 times higher in ELF than in water. Fe2+ enhanced organic radical yields by a factor of 20-80. Ascorbate mediated redox cycling of iron ions and sustained organic peroxide decomposition, as supported by kinetic modeling reproducing time- and concentration-dependence of organic radical formation, as well as by additional experiments observing the formation of Fe2+ and ascorbate radicals in mixtures of ascorbate and Fe3+. ·OH and superoxide were found to be efficiently scavenged by antioxidants.Wildfire PM mainly generated ·OH and R· with minor contributions from superoxide and oxygen-centered organic radicals (RO·). PM OP was high in wildfire PM, exhibiting very weak correlation with radical forms of ROS. These results were in stark contrast with PM collected at highway and urban sites, which generated much higher amounts of radicals dominated by ·OH radicals that correlated well with OP. By combining field measurements of size-segregated chemical composition, a human respiratory tract model, and kinetic modeling, we quantified production rates and concentrations of different types of ROS in different regions of the ELF by considering particle-size-dependent respiratory deposition. While hydrogen peroxide (H2O2) and ·O2- production were governed by Fe and Cu ions, ·OH radicals were mainly generated by organic compounds and Fenton-like reactions of metal ions. We obtained mixed results for correlations between PM OP and ROS formation, providing rationale and limitations of the use of oxidative potential as an indicator for PM toxicity in epidemiological and toxicological studies.Quinones and isoprene SOA activated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in macrophages, releasing massive amounts of superoxide via respiratory burst and overwhelming the superoxide formation by aqueous chemical reactions in the ELF. The threshold dose for macrophage activation was much smaller for quinones compared with isoprene SOA. The released ROS caused lipid peroxidation to increase cell membrane fluidity, inducing oxidative damage and stress. Further increases of doses led to the activation of antioxidant response elements, reducing the net cellular superoxide production. At very high doses and long exposure times, chemical production became comparably important or dominant if the escalation of oxidative stress led to cell death.ConclusionsThe mechanistic understandings and quantitative information on ROS generation by SOA particles provided a basis for further elucidation of adverse aerosol health effects and oxidative stress by PM2.5. For a comprehensive assessment of PM toxicity and health effects via oxidative stress, it is important to consider both chemical reactions and cellular processes for the formation of ROS in the ELF. Chemical composition of PM strongly influences ROS formation; further investigations are required to study ROS formation from various PM sources. Such research will provide critical information to environmental agencies and policymakers for the development of air quality policy and regulation.

Abstract Background White rot fungi produce various reactive oxygen species and ligninolytic enzymes for lignocellulose deconstruction. However, their interactions during the deconstruction of lignocellulosic structural barriers for efficient enzymatic saccharification remain unclear. Results Herein, the extracellular enzyme activities and secretomic analysis revealed the sequential expression of hydroxyl radical (⋅OH) and manganese peroxidases (MnPs) for lignocellulose deconstruction by the white rot fungus Irpex lacteus. Subsequently, in vitro functional studies found that ⋅OH possessed the ability to disrupt the smooth surface structure of corn stover, resulting in increased enzymatic saccharification and cellulose accessibility. Purified recombinant MnPs from I. lacteus were able to cleave the β-O-4 bond in phenolic and non-phenolic lignin model dimers without the help of any mediators. Furthermore, the sequential pretreatment of corn stover with ⋅OH and MnP exhibited significant synergistic effects, increasing enzymatic saccharification and cellulose accessibility by 2.9-fold and 1.8-fold, respectively. Conclusions These results proved for the first time the synergistic effects of ⋅OH and MnP pretreatment in improving the enzymatic saccharification and cellulose accessibility of corn stover. These findings also demonstrated the potential application of ⋅OH and MnP pretreatment for the efficient enzymatic saccharification of corn stover. Graphical Abstract

• Iron-binding ligands significantly stimulated superoxide production by Arthrobacter strains and other soil bacteria. • Fe(III)-DTPA effectively promoted the conversion of microbial superoxide into hydroxyl radicals. • A rough molar ratio of 1:1 between Fe(III) and DTPA was optimal for production of hydroxyl radicals. • The incorporation of DTPA into microbial cultures containing Fe(III) facilitated the degradation of oxytetracycline. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

• An updated review on ROS implicated in AOPs for pharmaceutical waste is presented. • Potential ROS are implicated in the pharmaceutical waste degradation. • Mechanistic insights regarding ROS-mediated reaction pathways are discussed. • The main detected transformation products of ACT using specific ROS are reported. 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. [ABSTRACT FROM AUTHOR]

• The mechanisms involved in the Fenton process were comprehensively elaborated. • The factors determining the influence of pH were emphatically illustrated. • We differentiate several Fenton-like process through their promoting mechanisms. • Substantive proposals toward future were proposed in this review. 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. [ABSTRACT FROM AUTHOR]

To understand the scavenging action of chlorophyll (Chla) found in most of the vegetables towards hydroxyl ( OH ∙ ) radicals, its reactions with OH ∙ radicals via RAF, HAT, and SET mechanisms have been investigated theoretically using two layer ONIOM [M06-2X/6-31G(d) (High):M06-2X/3-21G (Low)] method and M06-2X/6–311 + G(d,p) level of density functional theory. The molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) plots, HOMO–LUMO energy gap, global hardness (η), global softness (S), electronegativity (χ), and electrophilicity index (ω) of Chla molecule were computed and analyzed to determine its stability and reactive sites. It is found that RAF and HAT reactions are exergonic in both gaseous and aqueous media whereas SET reactions are endergonic in both media. However, all the RAF, HAT and SET reactions studied here are found to be more favourable in aqueous media vs. gas phase. The rate constants of RAF reactions at different sites are found to be of the order of ~ 6.2 × 107–1.8 × 1010 s−1 indicating that RAF reactions would be appreciably fast. This study concludes that chlorophyll can efficiently scavenge OH ∙ radicals preferably via RAF and HAT mechanisms and intake of water with chlorophyll can enhance its scavenging actions. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study was to synthesize a novel antibacterial and anticancer nanoformulation using aloe vera-derived carbon quantum dots (Cdot) and chromium-doped alumina nanoparticles (Al2O3:Cr/Cdot NPs) via a sol–gel method. X-ray diffraction (XRD) analysis confirmed crystalline NPs with a size range of 10–12 nm, while energy-dispersive X-ray spectroscopy (EDS) revealed their elemental composition without impurities. Fourier-transform infrared spectroscopy (FT-IR) indicated strong interactions between Cdot and Al2O3:Cr NPs, forming a robust heterostructure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images provided visual confirmation of monodisperse, spherical NPs, ensuring uniformity for further applications. Evaluation of reactive oxygen species (ROS) demonstrated superior generation of singlet oxygen and hydroxyl radicals by Al2O3:Cr/Cdot NPs, essential for photodynamic therapy. Minimum inhibitory concentration (MIC) tests revealed potent antibacterial activity against drug-resistant bacteria, inhibiting biofilm formation by 89% and 95% for MRSA and P. aeruginosa PAO1, respectively. Furthermore, the anticancer activity of Al2O3:Cr/Cdot NPs was assessed using C26 cells, demonstrating enhanced cytotoxicity upon UVA exposure. The NPs exhibited an inhibitory concentration (IC50) of 20 μg/mL without UVA exposure, decreasing to 10 μg/mL with UVA exposure, highlighting the synergistic effect of UVA light in enhancing cytotoxicity. Overall, these findings underscore the significant potential of Al2O3:Cr/Cdot NPs as multifunctional agents for addressing drug-resistant bacteria and advancing cancer therapy, offering promising avenues for nanomedicine research and development.

Gold nanoparticles (AuNPs) are increasingly recognized as theranostic agents in radiation oncology. Hence, the interaction of these nanoparticles with biomolecules viz DNA, RNA, and proteins needs to be investigated. In this study, the potential radioprotective role of AuNPs in preventing free radical-induced changes in bovine serum albumin (BSA) was investigated using ultraviolet–visible (UV–Vis) spectroscopy, fluorescence, Fourier-transform infrared (FTIR) spectroscopy, circular dichroism (CD), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) assay. γ-irradiation of the protein disrupts the ordered structure of the protein. AuNPs reduced the •OH-induced oxidation of tryptophan (Trp) to nearly half of that without the AuNPs. CD studies revealed that the % α helix of BSA post-irradiation in the presence of AuNPs was higher (62%) than that without AuNPs (53%). DTNB assay results showed that, following irradiation of BSA, 25% of the thiol content was retained in the presence of AuNPs, indicating that the thiol group was substantially protected with a retained thiol content of ~ 70%. This suggested that AuNPs protected the protein from degradation by scavenging the free radicals generated during radiation-induced oxidation.

Tumor tissues are well known for their unique high hydrogen peroxide (H2O2) microenvironment. How to exploit this tumor microenvironment for tumor cell killing is a question. In this study, a Mn-doped metal-organic framework (Mn-ZIF) was constructed. It possesses good peroxidase (POD) activity, which can oxidize tumor-localized H2O2 into hydroxyl radicals (·OH), that possesses the ability to directly kill tumor cells. More surprisingly, in vivo experiments the researchers not only observed the tumor-killing effect of Mn-ZIF, but also found it changes in macrophage phenotype in the tumor region. There was an increase in macrophage polarization towards the M1 subtype. This suggests that the tumor-killing effect of Mn-ZIF not only comes from its POD activity, but also regulates the immune microenvironment in the tumor region. In conclusion, the preparation of Mn-ZIF provides a new way for comprehensive tumor therapy. [ABSTRACT FROM AUTHOR]

Despite the vital roles of Fe0/biochar composites in the Fenton-like systems for eliminating pollutants that have been recognized, the contributions of persistent free radicals (PFRs) of carbon-based materials are typically overlooked. In this study, the high-PFR-containing biochar nanoiron composites were prepared (nZVI/500), and the in situ generation of hydroxyl radicals (·OH) and degradation of p-nitrophenol (PNP) were investigated. The results showed that nZVI/500 could effectively remove PNP in solution within the pH range of 3–8. Quantitative experiments of ·OH presented that, compared with low PFRs-containing composites, nZVI/500 could generate 64.6 µM ·OH in 60 min without any extra energy consumption. Mechanistic studies revealed that (1) both PFRs and Fe0 are able to utilize dissolved oxygen to generate H2O2 in situ; (2) PFRs can promote the cycling of Fe3+/Fe2+ in the system due to their strong electron exchange ability; and (3) PFRs directly transfer electrons to H2O2; therefore, the presence of PFRs accelerates the generation of ·OH in the system and facilitates the removal of PNP. This study provides an important theoretical basis and technical reference for expanding the application of PFR-rich carbon-based materials to remove environmental pollutants. [ABSTRACT FROM AUTHOR]

The environmental behavior of and risks associated with nanoplastics (NPs) have attracted considerable attention. However, compared to pristine NPs, environmental factors such as ultraviolet (UV) irradiation that lead to changes in the toxicity of NPs have rarely been studied. We evaluated the changes in morphology and physicochemical properties of polystyrene (PS) NPs before and after UV irradiation, and compared their hepatotoxicity in mice. The results showed that UV irradiation caused particle size reduction and increased the carbonyl index (CI) and negative charge on the particle surface. UV-aged PS NPs (aPS NPs) could induce the generation of hydroxyl radicals (·OH), but also further promoted the generation of ·OH in the Fenton reaction system. Hepatic pathological damage was more severe in mice exposed to aPS NPs, accompanied by a large number of vacuoles and hepatocyte balloon-like changes and more marked perturbations in blood glucose and serum lipoprotein, alanine aminotransferase and aspartate aminotransferase levels. In addition, exposure to PS NPs and aPS NPs, especially aPS NPs, triggered oxidative stress and significantly damaged the antioxidant capacity of mice liver. Compared with PS NPs, exposure to aPS NPs increased the number of altered metabolites in hepatic and corresponding metabolic pathways, especially glutathione metabolism. Our research suggests that UV irradiation can disrupt the redox balance in organisms by promoting the production of ·OH, enhancing PS NPs-induced liver damage and metabolic disorders. This study will help us understand the health risks of NPs and to avoid underestimation of the risks of NPs in nature. [Display omitted] [ABSTRACT FROM AUTHOR]

The widespread presence and use of Bisphenol A (BPA) in aquatic environments has caused significant ecological damage. Coal gangue (CG), a byproduct of coal mining, poses a major environmental concern due to its vast land occupation and potential for pollution. A magnetic recyclable geopolymer (MnFe2O4-CGP) using coal gangue geopolymer (CGP) as the carrier was successfully synthesized and was evaluated for its ability to Fenton-like degrade BPA. The characterization techniques revealed the successful incorporation of spherical MnFe2O4 onto the CGP surface and that CGP serves as an excellent platform for the immobilization and dispersion of MnFe2O4. The degradation rate reached 100% within 60 min at pH = 5, 15 mmol/L H2O2, 0.6 g/L catalyst, and 50 mg/L BPA, significantly higher than MnFe2O4 and CGP alone. It was indicated that the degradation rate of BPA in MnFe2O4-CGP composites was 0.1121 min−1, which was consistent with the first-order kinetic model. The saturation magnetization of MnFe2O4-CGP was measured to be 10.96 emu/g, enabling convenient recovery. MnFe2O4-CGP exhibited excellent stability, as the degradation rate of BPA remained above 95% even after five reaction cycles. This efficiency may be due to the MnFe2O4-CGP induced generation of reactive radicals. Quenching and EPR radical trapping experiments unequivocally confirmed that the reactive radical was hydroxyl radical (•OH). These results indicate that MnFe2O4-CGP has potential application prospects as a magnetic recyclable geopolymer composite in Fenton-like catalysis. [ABSTRACT FROM AUTHOR]

A radiation-self-Fenton system without the addition of H2O2 was developed for the efficient degradation of organic pollutants. We synthesized nickel-based metal–organic framework (Ni-BTC) as a catalyst for the in-situ generation of abundant hydroxyl radicals (·OH) and H2O2 under X-ray excitation, and the latter was further converted to ·OH in the Fenton reaction to synergistically accelerate the Methylene blue (MB) degradation. The embedded nickel sites and confined layered structure contributed to the stabilization and enrichment of ·OH within the framework. Consequently, the system could completely decolorize 150 mL of MB (20 mg/L) by absorbing 90 Gy dose. This study provided a novel technology for wastewater treatment. [ABSTRACT FROM AUTHOR]

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance is a multifaceted phenomenon and a serious threat to the prevailing global healthcare options. Photocatalytic therapy using nanotherapeutics is a promising alternative as this enables redox‐tuning of substrates inside biofilm while forming cytotoxic reactive oxygen species at hypoxic conditions. Herein, a new paradigm using the heterostructure of metal halide perovskite (PeV) nanocrystals is introduced by in situ capping with a nitric oxide (NO) releasing derivative (NTFA) and a •OH releasing phenothiazine ligand (BA‐PTZ) to yield NTFA@PeV@BA‐PTZ heterostructure. Material characterization, along with the mechanistic insights for the sunlight‐induced exciton formation, separation, and migration into respective molecular ligands inducing the catalytic generation of cytotoxic •OH/NO species are supported by in situ spectroscopic/microscopic studies. Encapsulation of NTFA@PeV@BA‐PTZ NCs with silica results NTFA@PeV@BA‐PTZ@SiO2, ensures its physiological stability and biologically benign nature. The efficacy of heterostructure toward biofilm inactivation and bactericidal activity are established through appropriate in vitro and in vivo biocompatibility, biodistribution, and assessment of antibacterial activity. The results also confirm the minimal toxicity and effective excretion of NTFA@PeV@BA‐PTZ@SiO2 from orally administered Balb/c mice. Together, based on manipulating the redox gradient omnipresent in bacterial/biofilm microenvironments and by catapulting the exciton‐mediated redox process, a proof‐of‐concept for an efficient multimodal photocatalytic nanotherapeutics is demonstrated. [ABSTRACT FROM AUTHOR]

We have found recently that two-step intrinsic hydroxyl radical (·OH)-dependent chemiluminescence (CL) could be produced by carcinogenic tetrahaloquinone and H 2 O 2. However, the first-step CL was too fast to clearly detect the stepwise generation of ·OH and CL, and to distinguish the exact dividing point between the first-step and second-step CL. Here we found that, extremely clear two-step intrinsic CL could be produced by the relative slow reaction of tetrabromohydroquinone (TBHQ) with H 2 O 2 , which was directly dependent on the two-step ·OH generation. Interestingly, the second-step, but not the first-step CL production of TBHQ/H 2 O 2 (CRET donor) was markedly enhanced by fluorescein (a typical xanthene dye, CRET acceptor) through a unique chemiluminescence resonance energy transfer (CRET) process. The novel CRET system of TBHQ/H 2 O 2 /fluorescein was successfully applied for the sensitive detection of TBHQ with the detection limit as low as 2.5 µmol/L. These findings will help to develop more sensitive and highly efficient CL or CRET systems and specific CL sensor to detect the carcinogenic haloquinones, which may have broad environmental applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The electronically nonadiabatic reaction of preassociation H + O + N2 ↔ OH* + N2 is the main channel of formation of electronically excited chemiluminescent OH* molecules during the oxidation of hydrogen in mixtures with a high content of nitrogen, e.g., during the combustion of hydrogen in air. For this reaction, within the framework of the combined theoretical and experimental approach with the use of the earlier results of quantum-chemical calculations for the rate constant of the elementary process H + O → OH* in the limit of high pressures and experimental data on OH* glow in N2-diluted H2/O2 mixtures (including those obtained in this work), a physically substantiated dependence of the rate constant on temperature and pressure has been obtained for a broad range of thermodynamic parameters (T = 200–4000 K and p = 10–3–102 atm). It has been shown that the found rate constant is in reasonable agreement with the existing results of measurements in both shock tubes and flames, with the rate constant in the process under study in a nitrogen buff er gas (M = N2) turning out to be nearly 1.3–1.8 times lower (at atmospheric pressure) than for M = Ar. It has been noted that in interpreting measurements of the temporal intensity profiles of OH* emission collected from the entire combustible volume (from the end of a shock tube), taking account of the self-absorption of emission on combustion products is substantial. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Using vacuum ultraviolet (VUV) to activate hydrogen peroxide (H2O2) to generate more reactive oxygen species (ROS) for decolonization and removal of dyes. The effects of H2O2 dosage, initial pH value of the solution, and initial dye concentration on the degradation of Acid Red G (ARG) and Rhoda- mine B (RhB) in the system were investigated. The results showed that when the dosage of H2O2 was 3 mmol/L, the decolorization rate of ARG and RhB at 80 mg/L could reach 96.3% and 98.4% respectively at 7 min. The removal rate of ARG and RhB increased with the increase of initial H2O2 concentration, but their promoting effect on the dye was limited when the concentration exceeded 3 mmol/L. The dye decolorization process follows a quasi first order kinetic model. Under acidic conditions, the decolorization and degradation of dyes have higher efficiency, while degradation is inhibited in alkaline environments. The free radical capture experiment and EPR detection results indicate that hydroxyl radicals (⋅ OH) and singlet oxygen (¹O2) are the main ROS, with ⋅ OH accounting for the main role.The presence of inorganic anions (HCO3, Cl-, NO3-, SO42-) can inhibit dye degradation. Through UV visible absorption spectroscopy analysis, it is preliminarily inferred that ARG is first attacked through the benzene ring, followed by the cleavage of azo bonds and naphthalene rings, and then mineralization;RhB mainly involves the destruction of conjugated structures, N-site deethylation, aromatic ring cracking, and mineralization. [ABSTRACT FROM AUTHOR]

In this study, a novel NiAl2O4/NiO@γ-Al2O3 catalyst was prepared by the impregnation-calcination method and used for the catalytic ozonation of tartrazine wastewater. The NiAl2O4/NiO@γ-Al2O3 catalyst were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption experiments. It was found that NiAl2O4/NiO@γ-Al2O3 significantly improved the removal of chemical oxygen demand of the dye wastewater from 40% for the direct ozone oxidation to 65%, and the ozone concentration depletion for catalytic ozonation was 120% of that for ozone alone. The catalytic activity of the catalyst did not significantly decrease after reuse for six cycles and leaching concentration of metal ions less than 1%. However, the toxicity of the dye wastewater was greatly reduced after the catalytic ozonation. The pyridine Fourier transform infrared spectroscopy showed the catalytic ozonation reaction was related with Lewis acid sites. The presence of hydroxyl radicals, superoxide anion radicals, and singlet oxygen was verified by an electron paramagnetic resonance, and the quenching experiments confirmed that the removal of organic pollutants from the tartrazine wastewater mainly relied on hydroxyl radicals and singlet oxygen. Therefore, the NiAl2O4/NiO@γ-Al2O3 could be an effective catalyst for the rapid catalytic ozonation of dye wastewater. [ABSTRACT FROM AUTHOR]

The combination of ozone and hydrogen peroxide (O3/H2O2), or the peroxone process, has often been used as an advanced oxidation process (AOP) in groundwater remediation and drinking water applications. This historical precedent sometimes leads to the misconception that H2O2 addition is required to achieve AOP conditions during ozonation. This is not the case for secondary or tertiary wastewater effluent applications, in which ozone reacts with abundant dissolved organic carbon (DOC) to generate hydroxyl radicals (∙OH). This study demonstrates the use of ozone with and without H2O2 addition to yield ∙OH exposures (up to 10−9 M-s) capable of achieving > 0.5-log10 attenuation of the industrial contaminant and probable human carcinogen 1,4-dioxane. This low molecular weight compound is commonly used as a surrogate when establishing AOP design criteria for potable reuse applications. DOC-normalized ozone doses (i.e., O3/DOC ratios) of ~ 1.0 and ~ 1.3 achieved 0.5-log10 attenuation of 1,4-dioxane with O3/H2O2 and O3, respectively. Also, a predictive model based on ∙OH exposure was accurate within approximately ± 10%. These results suggest that ozonation's role as an AOP, even in the absence of H2O2, should be acknowledged in regulatory frameworks to reduce unnecessary treatment redundancy and facilitate broader implementation of potable reuse. [ABSTRACT FROM AUTHOR]

The electronically nonadiabatic reaction of preassociation H + O + N2 ↔ OH* + N2 is the main channel of formation of electronically excited chemiluminescent OH* molecules during the oxidation of hydrogen in mixtures with a high content of nitrogen, e.g., during the combustion of hydrogen in air. For this reaction, within the framework of the combined theoretical and experimental approach with the use of the earlier results of quantum-chemical calculations for the rate constant of the elementary process H + O → OH* in the limit of high pressures and experimental data on OH* glow in N2-diluted H2/O2 mixtures (including those obtained in this work), a physically substantiated dependence of the rate constant on temperature and pressure has been obtained for a broad range of thermodynamic parameters (T = 200–4000 K and p = 10–3–102 atm). It has been shown that the found rate constant is in reasonable agreement with the existing results of measurements in both shock tubes and flames, with the rate constant in the process under study in a nitrogen buff er gas (M = N2) turning out to be nearly 1.3–1.8 times lower (at atmospheric pressure) than for M = Ar. It has been noted that in interpreting measurements of the temporal intensity profiles of OH* emission collected from the entire combustible volume (from the end of a shock tube), taking account of the self-absorption of emission on combustion products is substantial. [ABSTRACT FROM AUTHOR]

Non-thermal plasma (NTP) is gaining increasing attention as a promising approach for advanced water treatment to degrade persistent organic pollutants. Aqueous solutions of sulfamethoxazole (4-amino-N-(5-methylisoxazol-3-yl)-benzensulfonamide, SMZ), an antibiotic largely employed for humans and animals and a widespread persistent pollutant of waters and wastewaters, were subjected to air NTP treatment in a dielectric barrier discharge (DBD) reactor. The effects of SMZ initial concentration and of the solution pH on SMZ decomposition kinetics and transformation products were investigated. Efficient degradation was achieved, resulting in the complete removal of SMZ (10 µM initial concentration) in less than 25 min treatments, in the exhaustive mineralization (a result never reported before in plasma treatments and seldom reached also with other advanced oxidation processes) of all organic carbon in 6 h and in an energy efficiency of 6.4 g/kWh at 50% conversion. By means of HPLC-UV/Vis and LC-ESI-MSn analyses, a number of organic transformation products was identified along the path to SMZ mineralization, all present always in very small amounts and in turn decomposed at short treatment times. The effect of the solution pH on the genesis and decay of transformation products was also investigated. Based on comparisons with literature data and on previous findings obtained with the DBD reactor used in this work, it is concluded that the major reactive species involved in the degradation of SMZ are the hydroxyl radical and ozone. Finally, toxicological analyses of water initially containing 0.5 mMSMZ and subjected to 4 h NTP treatment showed that the by-products are not toxic to Raphidocelis subcapitata and Daphnia magna, while residual toxicity was detected by Aliivibrio fischeri. [ABSTRACT FROM AUTHOR]

Electrochemical advanced oxidation processes (EAOPs) offer several advantages over conventional Advanced Oxidation Processes (AOPs) such as UV/H 2 O 2 and H 2 O 2 /O 3. This includes the absence of chemical additives and ease of control. However, high energy consumption hampers the industrial application of EAOPs. Currently, the hydrogen generated at the cathode is vented and wasted, because of its low gas purity and difficulty in collecting it. But it also underscores an opportunity where the reactor design can be improved to facilitate the collection of high-purity hydrogen for energy savings. In our study, The EAOPs reactor was designed with a proton exchange membrane (PEM) for hydrogen generation. The hydrogen at the cathode chamber is then supplied to a fuel cell to generate electricity. The energy efficiency of the EAOPs-fuel cell system is evaluated through the wastewater treatment performance and energy saving that fuel cells achieve. To optimize the EAOPs-fuel cell system, various operational conditions, including different anode types, salt concentrations, and target organic compounds, were examined to optimize the system. Our experimental results indicate that the EAOPs-fuel cell system exhibits energy-efficient performance across various operational conditions. Notably, the highest energy efficiency and recovery ratio were achieved when operating at 3 V with boron-doped diamond (BDD) as the anode. Furthermore, we investigated the impact of mass transfer on the system's energy efficiency, considering both the initial organic concentration and flow velocity. This study provided valuable insights into combining the effect of EAOPs and hydrogen fuel cells, contributing to the understanding and optimizing the oxidation performance. It also contributes to developing sustainable and cost-effective advanced oxidation technologies with wide-ranging water treatment applications. • Collecting high-purity hydrogen during wastewater treatment. • Energy recovery is achieved with hydrogen fuel cells in the design of EAOPs system. • Comparison of four common anodes' oxidation performance for energy recovery purposes. • Analysis of the relationship between the current efficiency and energy efficiency. • Gave a direction for the future development of the EAOPs system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The objective of this study was to synthesize a novel antibacterial and anticancer nanoformulation using aloe vera-derived carbon quantum dots (Cdot) and chromium-doped alumina nanoparticles (Al2O3:Cr/Cdot NPs) via a sol–gel method. X-ray diffraction (XRD) analysis confirmed crystalline NPs with a size range of 10–12 nm, while energy-dispersive X-ray spectroscopy (EDS) revealed their elemental composition without impurities. Fourier-transform infrared spectroscopy (FT-IR) indicated strong interactions between Cdot and Al2O3:Cr NPs, forming a robust heterostructure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images provided visual confirmation of monodisperse, spherical NPs, ensuring uniformity for further applications. Evaluation of reactive oxygen species (ROS) demonstrated superior generation of singlet oxygen and hydroxyl radicals by Al2O3:Cr/Cdot NPs, essential for photodynamic therapy. Minimum inhibitory concentration (MIC) tests revealed potent antibacterial activity against drug-resistant bacteria, inhibiting biofilm formation by 89% and 95% for MRSA and P. aeruginosa PAO1, respectively. Furthermore, the anticancer activity of Al2O3:Cr/Cdot NPs was assessed using C26 cells, demonstrating enhanced cytotoxicity upon UVA exposure. The NPs exhibited an inhibitory concentration (IC50) of 20 μg/mL without UVA exposure, decreasing to 10 μg/mL with UVA exposure, highlighting the synergistic effect of UVA light in enhancing cytotoxicity. Overall, these findings underscore the significant potential of Al2O3:Cr/Cdot NPs as multifunctional agents for addressing drug-resistant bacteria and advancing cancer therapy, offering promising avenues for nanomedicine research and development. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) are increasingly recognized as theranostic agents in radiation oncology. Hence, the interaction of these nanoparticles with biomolecules viz DNA, RNA, and proteins needs to be investigated. In this study, the potential radioprotective role of AuNPs in preventing free radicalinduced changes in bovine serum albumin (BSA) was investigated using ultraviolet-visible (UV-Vis) spectroscopy, fluorescence, Fourier-transform infrared (FTIR) spectroscopy, circular dichroism (CD), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) assay. γ-irradiation of the protein disrupts the ordered structure of the protein. AuNPs reduced the •OH-induced oxidation of tryptophan (Trp) to nearly half of that without the AuNPs. CD studies revealed that the % α helix of BSA post-irradiation in the presence of AuNPs was higher (62%) than that without AuNPs (53%). DTNB assay results showed that, following irradiation of BSA, 25% of the thiol content was retained in the presence of AuNPs, indicating that the thiol group was substantially protected with a retained thiol content of ~ 70%. This suggested that AuNPs protected the protein from degradation by scavenging the free radicals generated during radiation-induced oxidation. [ABSTRACT FROM AUTHOR]