OH Generation Research Articles

Dual-Ligand-Driven Dark Reactive Oxygen Species Generation on Iron Oxyhydroxides: Implications for Environmental Remediation.

The dark generation of reactive oxygen species (ROS), particularly hydroxyl radicals (·OH), is crucial in the oxidative transformation of various pollutants. However, the mechanisms behind this process are predominantly linked to direct O2 activation by reduced substances such as Fe(II) and natural organic matter. In this study, we introduce a previously overlooked dual-ligand mechanism that significantly amplifies ·OH generation on iron oxyhydroxides, facilitated by cysteine and pyrophosphate. Our findings reveal that these ligands collaboratively boost ·OH generation by 99.5-125.7% compared to Fe(II) alone. This enhancement occurs through a two-step electron transfer (ET) process, where cysteine transfers electrons to O2 through iron oxyhydroxides. The complexation of pyrophosphate with iron oxyhydroxides further reduces the thermodynamic barriers, notably promoting this ET process and significantly improving the electron utilization efficiency for O2 activation by the electron donor cysteine. Such a process has shown its great potential for effectively driving the oxidative transformation of various pollutants, including As(III), dichlorophenol, and carbamazepine. These findings offer valuable insights for nature-based pollutant mitigation in soil and subsurface environments.

New Horizons in Micro/Nanoplastic-Induced Oxidative Stress: Overlooked Free Radical Contributions and Microbial Metabolic Dysregulations in Anaerobic Digestion.

Excessive production of reactive oxygen species (ROS) induced by micro/nanoplastics (MPs/NPs) is highly toxic to microbes. However, the mechanisms underlying ROS generation and metabolic regulation within anaerobic guilds remain poorly understood. In this study, we investigated the effects of environmentally relevant levels of polypropylene (PP)-MPs/NPs on oxidative stress and microbial ecology during anaerobic digestion (AD). Electron paramagnetic resonance spectroscopy revealed that PP-MPs/NPs elevated the concentrations of environmentally persistent free radicals (EPFRs) and derived hydroxyl radicals (•OH). EPFRs were identified as the primary contributors to •OH generation, as evidenced by a high Spearman correlation coefficient (r = 0.884, p < 0.001) and free radical-quenching studies. The formation of •OH enhanced ROS production by 86.2-100.9%, resulting in decreased cellular viability and methane production (by 37.5-50.5%) at 100 mg/g TS PP-MPs/NPs. Genome-centric metagenomic and metatranscriptomic analyses suggested that PP-MPs/NPs induced the reassembly of community structures, re-evolution of functional traits, and remodeling of interspecies interactions. Specifically, PP-MPs/NPs induced a shift in methanogen consortia from hydrogenotrophic Methanofollis sp. to acetoclastic and hydrogenotrophic Methanothrix soehngenii, primarily because of the latter's diverse ingestion patterns, electron bifurcation complexes, and ROS-scavenging abilities. Downregulation of genes associated with antioxidative defense systems (i.e., sodN, katA, and osmC) and ROS-driven redox signal transduction pathways (c-di-AMP and phosphorylation signaling pathways) provided insights into the mechanisms underlying ROS-induced microbial metabolic dysregulation. Our findings enhance the understanding of microbial ecological and metabolic traits under MPs/NPs stressors, facilitating the control of MPs/NPs toxicity and the stabilization of AD processes.

Critical impact of biochar on hydroxyl radical generation during humin oxidation

The production of hydroxyl radicals (·OH) via reduced humin oxygenation is well established. As biochar is widely used in environmental restoration, its coexistence with humin in restored soils may affect ·OH generation due to its electron transfer ability. However, the role of biochar in ·OH generation remains largely unexplored. Herein, we investigated the ·OH generation by humin-biochar at different mass ratios. Our results indicated that biochar could significantly enhance the ·OH production by humin when the mass of humin exceeded that of biochar. Notably, when the mass ratio of humin to biochar was 50, the ·OH produced reached 67.3 μM, which is nearly 1.5 times the amount generated by humin alone (43.1 μM). Both single-electron and two-electron transfer pathways coexisted in ·OH generation by humin-biochar. C = O in humin were necessary conditions for the production of ·OH, while the presence of C = C in biochar promoted the generation of ·OH. Using graphene and carbon nanotubes both rich in C = C groups as the model compounds, humin-graphene and humin-carbon nanotubes produced ·OH at 122 μM and 98.8 μM, respectively, significantly higher than those generated by humin alone (43.1 μM). This result confirmed the promoting effect of aromatic C = C bonds on ·OH generation. By contrast, when the biochar mass was greater than or equal to that of humin, ·OH generation was inhibited due to the significant reduction of C = O. In this case, environmentally persistent free radicals (EPFRs) in biochar were the primary structures responsible for ·OH production. This study provides comprehensive insights for the first time into the influence of biochar on ·OH generation by humin and offers a new potential method for the green and efficient removal of pollutants.

TME-Activated MnO2/Pt Nanoplatform of Hydroxyl Radical and Oxygen Generation to Synergistically Promote Radiotherapy and MR Imaging of Glioblastoma.

Radiotherapy (RT) is currently recognized as an important treatment for glioblastoma (GBM), however, it is associated with several challenges. One of these challenges is the radioresistance caused by hypoxia, whereas the other is the low conversion efficiency of the strongly oxidized hydroxyl radical (•OH), which is produced by the decomposition of water due to high-energy X-ray radiation. These factors significantly limit the clinical effectiveness of radiotherapy. To address these limitations, we developed a highly stable and efficient nanoplatform (MnO2/Pt@BSA). Compared to MnO2@BSA, this platform demonstrates high stability, a high yield of oxygen (O2), enhanced production of •OH, and reduced clearance of •OH. The system exhibited increased O2 production in vitro and significantly improved oxygen production efficiency within 100 s at the Pt loading of 38.7%. Furthermore, compared with MnO2, the expression rate of hypoxia-inducible factor (HIF-1α) in glioma cells treated with MnO2/Pt decreased by half. Additionally, the system promotes •OH generation and consumes glutathione (GSH), thereby inhibiting the clearance of •OH and enhancing its therapeutic effect. Moreover, the degradation of the nanoplatform produces Mn2+, which serves as a magnetic resonance imaging (MRI) contrast agent with a T1-weighted enhancement effect at the tumor site. The nanoplatform exhibited excellent biocompatibility and performed multiple functions related to radiotherapy, with simpler components. In U87 tumor bearing mice model, we utilized MnO2/Pt nanocatalysis to enhance the therapeutic effect of radiotherapy on GBM. This approach represents a novel and effective strategy for enhancing radiotherapy in gliomas, thereby advancing the field of catalytic radiotherapy and glioma treatment.

Self-catalytic enhancement of Cu-EDTA decomplexation and simultaneous Cu recovery via a dual-cathode electrochemical process

Heavy metals that are readily chelated with coexisting organic ligands in industrial wastewaters impose threats to environment and human health but are also valuable metal resources. Traditional treatment methods generally require additional chemicals and generate secondary contaminants. Here, a reagent-free dual-cathode electrochemical system was proposed for the efficient destruction of Cu-organic complexes and synchronous cathodic recovery of Cu, whereby in situ production of H2O2 at carbon aerogel (CA) cathode was coupled with the reduction of Cu(II) to Cu(I) and finally to Cu(0) at Ti cathode. The intermediate Cu(II) complexes enabled the self-reinforced degradation owing to their higher activities toward •OH generation by activating H2O2 in contrast to initial Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The enhanced production of Cu(I) by Ti cathode facilitated both •OH and Cu(III) formation, and the copper redox cycle was realized in the self-reinforced system, maintaining its sustainable catalytic activity. The energy cost of the dual-cathode system is 0.011 kWh/g for decomplexation and 0.057 kWh/g for Cu recovery, which is much lower than single Ti or CA cathode system. This established process provides a prospective approach for cost-effective destruction of chelating metal complexes and metal resources recovery from heavy metal wastewaters.

Emerging contaminants removal through fluorine-doped carbon hollow fiber microfiltration membrane based on metal-free electro-Fenton

The emerging contaminants with high toxicity and bioaccumulation potentially threaten to human health, which was difficult removed by traditional biological treatment or membrane separation. In view of this, a novel type of fluorine (F)-doped carbon hollow fiber microfiltration membrane was prepared for realizing emerging contaminants removal through metal-free electro-Fenton. Herein, polyaniline (PANI) was used as a precursor for preparation of porous carbon membrane. The graphitic N and pyridinic N on porous carbon were used as the active sites for H2O2 production and its further activation to ·OH, which realized metal-free electro-Fenton reaction. According to the results, the carbon nanotubes with F-PANI at the ratio of 1:1 and calcination temperature at 300°C endowed the membrane moderate resistance and pure water permeability of 430 Ω and 48.51 L/(m2·h·bar), respectively. Importantly, the intensity of ·OH generation was further significant enhanced by introducing C-F bonding into the membrane. Therefore, the bisphenol A (BPA), sulfamethoxazole (SMZ) and atrazine (ATZ) removal rates were 92.63%, 38.47% and 27.05%, respectively. For control group without bias, the removal rates of above contaminants were 0% removal rates. Moreover, the membrane permeate loss by filtrating BPA, SMZ and ATZ were 0.13, 0.15 and 0.05, which were 0.20, 0.24 and 0.21 for control group.

Spider Webs‐Inspired Aluminum Coordination Hydrogel Piezoionic Sensors for Tactile Nerve Systems

AbstractPiezoionics, a new frontier that employs mobile ions as energy and charge carriers, plays an important role in new energy and intelligent electronics. However, a significant challenge consists in balancing the structural design of metal ions coordination hydrogel (HG‐MI) piezoionics for current conduction, voltage generation, and especially mechanical adaptability. Herein, inspired by the spider webs' unique structure, a strategy by realizing the full potential of metal‐ligand ions ([(OH)Cl2]3−) to facilitate the keggin‐type structure AlOHAlOH generation together with activate functional carboxyls is introduced. Impressively, the whole property of the product HG‐AlPAC, especially the mechanical performance is improved. For example, the toughness of HG‐AlPAC is 2.75 MJ m−3, more than twofold that of traditional HG‐AlAS/AC/AN samples. Due to the stable fixation of ─Al─OH─ thus promoting Cl− separation upon external force, HG‐AlPAC achieves a piezoionic coefficient of 0.89 mV KPa−1 and energy conversion efficiency of 1.29%, promising for mechanical‐electrical conversion and sensing. Combined with the good mechanical performance with the excellent piezoionic properties, underscores its potential as a tactile nerve system of analgesia patients to prevent them from being injured. This work intends to provide a stride toward mechanically robust self‐powered piezoionic sensors and offer insights into ionotropic materials for energy harvesting, human‐machine interaction, and biointerface.

Supramolecular PEG-DNA-Ferrocene Nanogels for Synergistically Amplified Chemodynamic Therapy via Cascade Reactions.

Chemodynamic therapy (CDT) has been limited by the tumor microenvironment, such as the low concentration of hydrogen peroxide (H2O2). The combination of therapeutic strategies that increase H2O2 with CDT can synergistically enhance the therapeutic effect. Herein, a novel supramolecular PEG-DNA-ferrocene nanogel that can codeliver glucose oxidase (GOx) and the hypoxia-activable prodrug tirapazamine (TPZ) was developed to synergistically amplify CDT via cascade reactions. The DNA nanogel was size-controllable and DNase I-responsive and exhibited good biocompatibility. Induced by oxygen consumption and H2O2 generation in the catalytic reaction of GOx, the drugs TPZ and ferrocene in the nanogel underwent the hypoxia-based reaction and the Fenton reaction, respectively. The vitro model tests, intracellular ROS test, MTT experiments, and DNA damage assay demonstrated that the H2O2-based cascade Fenton reaction and the hypoxia-based cascade reaction obviously increased ·OH generation and promoted the apoptosis of cancer cells. This cascade supramolecular nanoplatform provided a promising therapeutic strategy to synergistically amplify CDT.

Experimental and reaction mechanism study on laminar burning velocity and characteristics of OH/NH generation in ammonia co-combustion

Developing fuels without carbon, such as ammonia (NH3), is crucial for achieving carbon reduction. Laminar burning velocity (LBV) is investigated, and distribution characteristics of OH and NH radicals are identified through planar laser-induced fluorescence. Rate of production of main free radicals and sensitivity analysis are also studied. The addition of NH3 to CH4-air mixtures results in a decrease in the LBV, a rise in preheating zone height, a reduction in OH radical fluorescence intensity, and an enhancement in NH radical fluorescence intensity. Simulation reveals that the high NH3 ratio enhance the negative impact of nitrogen-containing elementary reactions on LBV. The addition of NH3 enhances the initial consumption of more OH via reaction R248:NH2+OH=NH+H2O, leading to increased NH production, and indicating a negative effect on LBV. The decrease in OH concentration is the main factor leading to a decrease in LBV. The reactions affecting the OH generation and consumption are R39:H+O2=O+OH and R85:OH+H2=H+H2O, respectively. The addition of NH3 leads to a more significant reduction in R39.

Double Enzyme Active Hydrogel Program Regulates the Microenvironment of Staphylococcus aureus-Infected Pressure Ulcers.

The treatment of infected pressure ulcers (IUPs) requires addressing diverse microenvironments. A pressing challenge is to effectively enhance the regenerative microenvironment at different stages of the healing process, tailoring interventions as needed. Here, a dual enzyme mimetic and bacterial responsive self-activating antimicrobial hydrogel designed to enhance IPUs healing is introduced. This hydrogel incorporates pH-responsive dual enzyme-active nanoplatforms (HNTs-Fe-Ag) encapsulated within a methacrylate-modified silk fibroin (SFMA) and dopamine methacrylamide (DMA) matrix. This composite hydrogel exhibits adaptive microenvironment regulation capabilities. Under the low pH microenvironment of bacterial infection, it has excellent antimicrobial activity by self-activating the •OH generation in conjunction with photothermal effects. Under the neutral and alkaline microenvironment of chronic inflammation, it catalyzes the decomposition of hydrogen peroxide (H2O2) to produce oxygen (O2), thereby alleviating hypoxia and scavenging reactive oxygen species (ROS), which in turn remodulates the phenotype of macrophages. The composite hydrogel demonstrates on-demand therapeutic effects in the microenvironment of infected wounds, significantly enhancing the regenerative microenvironment of IUPs by promoting wound closure, inflammation regulation, and collagen deposition through self-activated antimicrobial action during infection and adaptive hypoxia relief during recovery. This approach offers a novel strategy for developing smart wound dressings.

Fabrication of boron modified bi-functional air diffusion electrode for ciprofloxacin degradation: In-situ H2O2 generation and self-activation

In order to improve H2O2 in-situ generation in electrochemical system, a boron (B) modified air diffusion electrode (B@ADE) was fabricated in the present study. Carbon black (CB) doped by B was deposited on ADE surface as catalytic layer. Performance of B@ADE with different B/C mass ratios has been investigated and 0.3 was identified as the optimal one·H2O2 yield can be achieved 204.85 mg L-1 within 45 min at 0.3-B@ADE, which was 1.51 times for that of ADE. Meanwhile, H2O2 self-activation on B@ADE surface was observed and effects of different operating parameters on •OH formation have been analyzed. XPS analyzation demonstrated that BC2O, BC2O and C=O/O-C=O were related to H2O2 generation. DFT calculation revealed that BCO2 was benefit for O2 adsorption, while BC2O promoted *OOH desorption with lower free energy barriers for H2O2 and •OH generation. Quenching experiments for ciprofloxacin (CIP) demonstrated that •OH, O2•- and 1O2 were co-existed in the system with their contribution quantified. Four possible degradation pathways were proposed through active sites identification by DFT calculation and intermediates detection by HPLC-MS/MS. Bio-toxicity analyzation results showed that the toxicity of most intermediates was lowered than CIP. These results proved that electrochemical oxidation system with B@ADE enhanced in-situ H2O2 generation and self-activation, with great potential for practical application.

Hydroxyl Defects-Mediated Hydrolytic Activation of Peroxydisulfate Under Nanoconfinement: Role of Lewis Basic Sites for Altering the Photosensitized Species and Pathways.

Herein, the pivotal mechanism of defect engineering-mediated triazine-based conjugated polymers (TCPs) is comprehensively elucidated for photosensitized activation of peroxydisulfate (PDS) under nanoconfinement by encapsulating the defective polymer framework into the nanochannel of SBA-15 (d-TCPs@SBA-15). The incorporated hydroxyl defects (-OH defects) substantially accelerate the accumulation of electrons at -OH defects, forming the Lewis basic sites. Due to the facilitated elongation of the S─O bond and reduced energy barrier of SO5* generation, the captured PDS undergo prehydrolysis process, oxidized into O2 - and 1O2 by surrounding h+, thereby setting apart from the conventional reductive activation of SO4 -/•OH generation occurred in pristine TCPs (p-TCPs). Crucially, this work represents a pioneering effort in exploring the PDS activation pathway upon the defective polymer under the nanoconfinement to leverage kinetic merits of slow photon effect and reactive oxygen species (ROSs) enrichment, and the novel prehydrolysis activation mechanism involved may catalyze the rational design of photocatalysts featuring Lewis-acid/base centers.

Electrochemical generation of H*-•OH redox pair for rapid removal of refractory nitro-organic micropollutants

This study developed an innovative reduction-oxidation coupling process for treatment of refractory organic wastewater. We constructed a series of N5-coordinated transition metals (TMs) (TMs = Mn, Fe, Co, Ni, Cu) single-atom sites supported on nitrogen-rich carbon nitride (SA-TM-C3N5) for electrochemical generation of the surface-adsorbed hydrogen atom (H*) and hydroxyl radical (•OH). The SA-Co-C3N5 exhibited the highest activity for production of the H*-•OH redox pair, which effectively degraded refractory nitro-organic micropollutants via the parallel reduction-oxidation pathways. The SA-Co-C3N5-mediated electro-Fenton-like system showed high removal efficiency (99 %) and mineralization capacity (78 %) toward metronidazole (MNZ) with low energy consumption (0.019 kWh (g TOC)–1). The trifunctional properties of the H* have contributed to the reduction of nitro compounds, the 2e– ORR for H2O2 production and the Fenton-like catalysis for •OH generation. This work sheds lights on the development of advanced reduction-oxidation coupling process for green and sustainable water purification.

Mechanism of ozone catalysis by transition metal hydroxyl oxides: From reactive oxygen species to surface structural hydroxyl

Transition metal hydroxyl oxides have been used widely as ozone catalysts for water purification. However, the fabrication methods selected and the pollutants treated vary, making it difficult to compare their performance. In this study, ZnOOH, FeOOH, CoOOH, and MnOOH were synthesized by the same method to remove multiple structurally similar targets. Results showed that the ZnOOH performed the best, removing over 90% of all targets within 40min, and presenting the highest ozone utilization rate of 0.081min-1. Multiple ROS quantification and contribution experiments jointly demonstrated that ZnOOH had an advantage over the other catalysts only in ·OH generation, but the ·OH contributed 93% of target removal in the ZnOOH/O3 process. Structure analysis of ZnOOH suggested that its ·OH generation had little connection with the contents of surface metal and adsorbed water, but was dependent on the surface structural hydroxyl that would undergo loss at 100-300℃. This concentration of ZnOOH was 10.1mM/g, which was 1.7, 5.3, and 6.3 times higher than that of FeOOH, CoOOH, and MnOOH, respectively. Heat treatment further revealed that these surface hydroxyl mainly originated from the hydroxyl ions from water dissociation and could regenerate timely during reuse. Finally, a possible catalysis pathway was proposed.

FeSA‐Ir/Metallene Nanozymes Induce Sequential Ferroptosis‐Pyroptosis for Multi‐Immunogenic Responses Against Lung Metastasis

For cancer metastasis inhibition, the combining of nanozymes with immune checkpoint blockade (ICB) therapy remains the major challenge in controllable reactive oxygen species (ROS) generation for creating effective immunogenicity. Herein, new nanozymes with light-controlled ROS production in terms of quantity and variety are developed by conjugating supramolecular-wrapped Fe single atom on iridium metallene with lattice-strained nanoislands (FeSA-Ir@PF NSs). The Fenton-like catalysis of FeSA-Ir@PF NSs effectively produced •OH radicals in dark, which induced ferroptosis and apoptosis of cancer cells. While under second near-infrared (NIR-II) light irradiation, FeSA-Ir@PF NSs showed ultrahigh photothermal conversion efficiency (𝜂, 75.29%), cooperative robust •OH generation, photocatalytic O2 and 1O2 generation, and caused significant pyroptosis of cancer cells. The controllable ROS generation, sequential cancer cells ferroptosis and pyroptosis, led 99.1% primary tumor inhibition and multi-immunogenic responses in vivo. Most importantly, the inhibition of cancer lung metastasis is completely achieved by FeSA-Ir@PF NSs with immune checkpoint inhibitors, as demonstrated in different mice lung metastasis models, including circulating tumor cells (CTCs) model. This work provided new inspiration for developing nanozymes for cancer treatments and metastasis inhibition.

Hierarchically ordered porous carbon crystals for nanoconfined and sustainable fenton oxidation of water pollutants

In this work, we developed a hierarchically multi-faceted ordered porous carbon crystal (HOPC) for generating a favorable chemical microenvironment to intensify both Fe3+ binding and H2O2 utilization efficiency. The confined pore space and surface functionality enable •OH and micropollutants to be concentrated in the pores, thus significantly accelerating pollutant degradation kinetics (0.034 min−1) with reduced chemical consumption (0.081 mM H2O2). Theoretical calculations and in-situ characterizations reveal that both CO and pyrrolic N act as active sites bridging Fe3+, facilitating the transfer of outermost e− from the p-orbital of active sites (O and N) to the d-orbital of iron, effectively reducing Fe3+ to Fe2+ and enhancing the open-circuit potential of HOPC-Fe3+ complexes, as well as facilitating e− extraction from H2O2. For the first time, H2O2 was unveiled to be both an electron donor and acceptor to cooperate with the iron redox cycle for sustainable •OH generation toward fast pollutant decontamination.

The interplay of Brown carbon (BrC) surrogates and copper: Implications for the oxidative potential of ambient particles

Atmospheric particulate matter (PM) poses adverse effects on human via producing reactive oxygen species (ROS). Oxidative potential (OP, ability to generate ROS) can be induced by various chemicals in PM, while their interplay remains poorly characterized. Here, we systematically assessed influences of Cu2+ on OP of Brown carbon (BrC) (e.g., imidazoles) using dithiothreitol (DTT) assay. Results showed DTT consumption rate exhibited an initial rise and later decline (0.25 −0.56 µM/min) along with increase of BrC concentration (0.1 − 2 µM), while no general trend was observed for •OH formation. Although Cu2+ showed either antagonism or synergism with BrC against DTT consumption, Cu2+ displayed antagonism with most BrC against •OH generation. Fluorescence quenching experiments provided evidence of complexation between Cu2+ and water-soluble organic compounds (WSOCs, from ambient PM2.5), which was influenced by Cu2+ concentration. Further parallel factor analysis of spectra showed that polycarboxylate-type humic acid-like substances (complexation site number (n): 0.46, complexation equilibrium constant (k): 0.51) and fulvic acid-like compounds (n: 0.42, k: 0.62) were the main components in WSOCs that complexed with Cu2+. Our results suggest the interactions of BrC and copper play a crucial role in PM OP and highlight complexation in evaluation of PM OP.

Experiment and kinetics study on OH∗ chemiluminescence up to 3150 K in hydrogen combustion behind reflected shock waves

Chemiluminescence of OH∗ is commonly employed as an optical indicator for the combustion process. It is widely recognized that the generation of OH∗ in hydrogen flames is primarily governed by the reaction H + O + M=>OH∗+M. In this study, the time histories of OH∗ chemiluminescence from the A→X band around 308 nm were recorded behind reflected shock waves for stoichiometric and lean H2/O2 mixtures highly diluted in argon over the temperature range of 1130–3150 K and at the pressure of approximately 0.9 atm. Based on the time histories of OH∗ chemiluminescence, the best-fit reaction rate coefficient for the reaction H + O + M=>OH∗+M was determined as k = 3.17 × 1027exp(-121968 cal mol−1/RT) + 2.25 × 1017exp(-4246 cal mol−1/RT) cm6 mol−2 s−1 over the temperature range studied. Furthermore, by using the current rate coefficient in mechanism predictions, the predicted time histories and relative peak intensities of OH∗ chemiluminescence are in good agreement with experimental results reported in literature.

The Overlooked Role of Humin in Dark Hydroxyl Radical Production during Oxygenation.

Humin, endowed with abundant redox functional groups, can be reduced anaerobically under dark. When reduced humin encounters O2, the possibility of ·OH formation arises. However, the exploration of ·OH generation mediated by humin has not been comprehensively conducted. The study found that O2 oxidized the reduced humin, generating 8.61 μmol/g of ·OH. After isolating humin using the methyl isobutyl ketone (MIBK) method, the lipid component was identified as the primary contributor to ·OH generation. Subsequent polar separation revealed that the lipid fraction extracted from the ethanol-water mixture with a volume ratio of 7:3 (LFEW7:3) played the most significant role in ·OH production. Further characterization confirmed that the simultaneous presence of aromatic C═C and C═O were the predominant features contributing to the ·OH generation. The ·OH generation experiments with humin-pyridine analogue compound demonstrated that polycyclic pyridine N (≥3 rings) played a significant role in promoting the ·OH generation. Most importantly, the study compared the ·OH production by humin and homologous humic acid, indicating that ·OH generated by humin was higher than that of humic acid. Overall, these affirmative findings manifested the overlooked role of humin in ·OH production and offered valuable insights into the mechanism of ·OH generation by humin in the dark.

Domestic wastewater treatment towards reuse by “self-supplied” microbial electrochemical system assisted UV/H2O2 process

Domestic wastewater is a potential source of water for non-potable reuse that may help address the global water, energy, and resource challenges. Herein, a “self-supplied” process through integrating microbial electrochemical system (MES) with UV/H2O2 was developed and investigated for wastewater treatment. H2O2 was “self-supplied” from MES while the MES catholyte was “self-supplied” from the final effluent of UV/H2O2. It was found that the MES accomplished > 80 % degradation of chemical oxygen demand (COD) through bioanode degradation, and produced 18 - 20 mg L−1 H2O2 via oxygen reduction reaction in the gas diffusion cathode. The MES effluent was further treated by the UV/H2O2 process, which achieved the complete removal of recalcitrant diclofenac and > 6 log inactivation of Escherichia coli. The enhanced treatment performance of UV/H2O2 was demonstrated via a comparison with the control experiments (UV or H2O2 treatment) and benefited from ·OH generation and sulfide removal. When treating the actual wastewater, the proposed system exhibited consistent treatment performance for the organic compounds and recalcitrant contaminants, and the quality of the treated water would meet the non-potable water reuse guidelines. The results of this study encourage the further exploration of emerging contaminant removal, system coordination, and use of renewable energy by the cooperation between MES and UV/H2O2.