OH Production Research Articles

Rice straw returning enhances cadmium activation by accelerating iron cycling thus hydroxyl radical production in paddy soils during drainage

Straw returning is widely found elevating the bioavailability of cadmium (Cd) in paddy soils with unclear biogeochemical mechanisms. Here, a series of microcosm incubation experiments were conducted and spectroscopic and microscopic analyses were employed. The results showed that returning rice straw (RS) efficiently increased amorphous Fe and low crystalline Fe (II) to promote the production of hydroxyl radicals (OH) thus Cd availability in paddy soils during drainage. On the whole, RS increased OH and extractable Cd by 0.2–1.4 and 0.1–3.3 times, respectively. While the addition of RS effectively improved the oxidation rate of structural Fe (II) mineral (i.e., FeS) to enhance soil Cd activation (up to 38.5 %) induced by the increased OH (up to 69.2 %). Additionally, the existence of CO32− significantly increased the efficiency level on OH production and Cd activation, which was attributed to the improved reactivity of Fe (II) by CO32− in paddy soils. Conclusively, this study emphasizes risks of activating soil Cd induced by RS returning-derived OH, providing a new insight into evaluating the safety of straw recycling.

Additional HONO and OH Generation from Photoexcited Phenyl Organic Nitrates in the Photoreaction of Aromatics and NOx.

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NOx. Significant HONO (1.56-4.52 ppb) and OH production is observed during the photoreaction of different kinds of aromatics with NOx (18.1-242.3 ppb). We propose an additional mechanism involving photoexcited phenyl organic nitrates (RONO2) reacting with water vapor to account for the higher levels of measured HONO and OH than the model prediction. The proposed HONO formation mechanism was evidenced directly by photolysis experiments using typical RONO2 under UV irradiation conditions, during which HONO formation was enhanced by relative humidity. The 0-D box model incorporated in this mechanism accurately reproduced the evolution of HONO and aromatic. The proposed mechanism contributes 5.9-36.6% of HONO formation as the NOx concentration increased in the photoreaction of aromatics and NOx. Our study implies that photoexcited phenyl organic nitrates are an important source of atmospheric HONO and OH that contributes significantly to atmospheric oxidation capacity.

Mn single atoms for one-electron photoozonation of aqueous organics

Photocatalytic ozonation offers a potential approach for highly efficient organic degradation by in-situ generation of reactive •OH via electron reduction of ozone. Herein, we synthesized a Mn single atom photocatalyst for promoting the •OH generation from O3 activation under visible light irradiation. Theoretical calculation and experimental studies reveal that Mn single atoms on carbon nitride significantly promote the excitation and transfer of photo-generated electrons, making charge carriers enriched around MnN4 sites and shortening their migration path to participate in surface reactions. Meanwhile, Mn single atoms serve as adsorption and catalytic sites for O3, favoring a fast one-electron-reduction reaction kinetics. More importantly, the trade-off between the number of available electrons and active sites in photocatalytic performance was observed from regulating the density of Mn single atoms. This work offers an intriguing regulation strategy for enriching surface charges on single atom catalyst interface toward efficient •OH production and removal of aqueous organics.

Enhanced nitrous acid (HONO) formation via NO2 uptake and its potential contribution to heavy haze formation during wintertime

A full understanding of the sources of atmospheric nitrous acid (HONO) in the polluted urban atmosphere remains a challenge. In this study, ambient HONO and relevant species were measured during January 2019 at an urban site in Beijing, China, and a budget analysis of HONO was conducted using a box model combined with field observations. Large nighttime “missing sources” of HONO were identified on heavily polluted days based on traditional sources, which had a significant correlation with the relative humidity, ammonia (NH3), and aerosol surface area, and the promotional effect of NH3 for nitrogen dioxide (NO2) uptake on the wet aerosol surface was discussed. Then, an updated parameterization scheme for quantifying the enhanced heterogeneous reactions of NO2 on aerosol surfaces is proposed, and the missing nighttime sources of HONO could be substantially compensated after the new scheme was incorporated. Further evaluation on the contributions of HONO to hydroxyl radicals was conducted, and the authors found that the photolysis of HONO played a dominant role in the primary OH production on the polluted days (78%–90%). The study reveals great potential of an NH3-enhanced uptake coefficient of NO2 on the aerosol surface in the nocturnal HONO budget, and highlights the significance of HONO in the strong atmospheric oxidation capability during episodes with a heavily polluted atmosphere.摘要本文研究了重污染过程中气态亚硝酸 (HONO) 的关键来源并基于化学箱模型对其源汇过程进行了闭合分析. 结果显示, 现有的HONO 源汇机制并不能解释观测期间出现的高HONO事件, 尤其是重污染过程夜间存在大量的HONO "未知源". 本文提出了一套新的HONO 源汇参数化方案, 可以较好的模拟观测期间HONO日间和夜间来源, 并进一步评估了HONO 对羟基自由基 (OH) 的贡献, 发现 HONO 光解主导了重污染天OH生成 (78%–90%). 研究结果揭示了华北城市富氨大气环境促进 NO2在气溶胶表面的摄取和非均相反应进而主导了夜间HONO生成, 凸显了HONO化学对于重污染过程维持大气氧化能力的重要作用.

A direct Z-scheme 0D α-Fe2O3/TiO2 heterojunction for enhanced photo-Fenton activity with low H2O2 consumption

The insufficient F(III)/Fe(II) cycling rate resulted from high combination of photogenerated carriers severely hinders the photo-Fenton activity. In this work, 0 dimensional α-Fe2O3 nanoclusters decorated TiO2 heterojunction (FT-x) was prepared via in-situ phase transformation strategy. FT-200 exhibited the optimal photo-Fenton activity for 2,4-dichlorophenol degradation with the kinetic rate constant reaching 1.0806 min−1 under low H2O2 dosage (1 mmol/L), which was 126.1 and 202.8 times higher than that of TiO2 and α-Fe2O3. Radical quenching experiments and electron spin resonance spectra proved that ·OH was the leading reactive specie. The enhanced photo-Fenton activity was attributed to the accelerated F(III)/Fe(II) cycling rate induced by the direct Z-Scheme charge transfer mechanism. Benefiting from the abundant ·OH production, the dechlorinate ratios and mineralization ratios of multiple chlorophenol pollutants (2,4-dichlorophenol, 4-chlorophenol, 2,4,6-trichlorophenol) all exceeded 98 %. The biotoxicity of chlorophenol wastewater was greatly reduced after the treatment by Light/H2O2/FT-200 system. Overall, this work constructed a low-cost and highly efficient photo-Fenton system for refractory organic wastewater treatment.

Study on Oxidation Activity of Hydrogenated Biodiesel–Ethanol–Diesel Blends

In the pursuit of understanding the oxidation mechanisms of hydrogenated biodiesel fuels and elucidating the combustion behavior of biomass fuels when blended with diesel, this study presents a comprehensive investigation into the reaction mechanism of hydrogenated biodiesel–ethanol–diesel mixtures. We develop a comprehensive reaction mechanism encompassing 187 components and 735 reactions for hydrogenated biodiesel–ethanol–diesel mixtures. Through kinetics analysis under varied conditions, including 1.0 MPa pressure, an equivalence ratio of 1.0, and temperatures of 900 K and 1400 K, we explore the impact of cross-reactions and changing fuel blend ratios on low- and high-temperature oxidation. Our findings indicate that oleic and stearic acid methyl esters serve as better substitutes for representing hydrogenated biodiesel kinetics than methyl decanoate. At lower temperatures, increased hydrogenated biodiesel and ethanol content leads to reduced OH generation, impacting reactivity. Conversely, higher temperatures result in enhanced OH production with increased hydrogenated biodiesel and ethanol concentrations, promoting reactivity. A cross-reaction analysis reveals CH2O as a prominent product, with the CH2O→HCO→CO pathway playing a pivotal role. In summary, our research unveils the intricate oxidation mechanisms of hydrogenated biodiesel–ethanol–diesel mixtures, providing insights into their combustion characteristics and offering implications for optimizing fuel blends for cleaner and more efficient energy solutions.

Dependence of Biotic and Abiotic H2O2 and •OH Production on the Redox Conditions and Compositions of Sediment during Oxygenation.

Reactive oxygen species (ROS) production in O2-perturbed subsurface environments has been increasingly documented in recent years. However, the constraining conditions under which abiotic and/or biotic mechanisms predominate for ROS production remain ambiguous. Here, we demonstrate that the ROS production mechanism, biotic and abiotic, is determined by sediment redox properties and sediment compositions. Upon the oxygenation of 10 field sediments, the cumulative H2O2 concentrations reached up to 554 μmol/kg within 2 h. The autoclaving sterilization experiments showed that H2O2 could be produced by both biotic and abiotic processes depending on the redox conditions. However, only the abiotic process could produce significant levels of •OH, and the production yield was closely related to the sediment components, particularly sediment Fe(II) and organic matter. Fe(II) bound with organic matter led to high yields of H2O2 and •OH production. Sediment oxygenation contributed to the appearance of H2O2 in groundwater, with the abiotic mechanism producing higher instantaneous H2O2 concentrations than the biotic mechanism. These findings reveal that the redox conditions, compositions, and texture of sediments collectively control abiotic and biotic mechanisms for ROS production, which assists the identification of ROS production hotspots and the understanding of ROS distribution and utilization in the subsurface.

Electrocatalytic degradation of Favipiravir by heteroatom (P and S) doped biomass-derived carbon with high oxygen reduction reaction activity

In this study, a biomass-derived carbon block with heteroatoms (P and S) self-doped graphene structure was successfully synthesized by spent coffee grounds (SCG) directly sintered method. The spent coffee grounds biomass-derived carbon (SCC) block was used as electrocatalytic electrode to effectively degrade the antiviral drug of Favipiravir (FAV) in water, which represented excellent oxygen reduction reaction (ORR) activity with the H2O2 production. The doped heteroatoms in the graphene structure of SCC provided many active sites in the electrocatalytic electrode for ORR as well as more production of reactive OH･. Based on the structural characterization, radical species identification and intermediate products analysis, the reaction mechanism of FAV degradation by the SCC block electrode was proposed. This catalytic system also showed high ecological safety that the ecological toxicity for Vibrio fischeri was significantly reduced with the degradation process of FAV. The degradation of FAV in recycle test and in real sample of lake water, well water, tap water all demonstrated high stability of structure and catalytic activity of SCC. The electrocatalytic system based on SCC block electrode has realized the recycling and utilization of biomass resources and has promising application on the removal of environmental pollutants.

The Effects of ≡Ti–OH Site Distortion and Product Adsorption on the Mechanism and Kinetics of Cyclohexene Epoxidation over Ti/SiO2

The Effects of ≡Ti–OH Site Distortion and Product Adsorption on the Mechanism and Kinetics of Cyclohexene Epoxidation over Ti/SiO₂

An Enzyme‐Engineered Coppery Nanozyme for High‐Efficiency Mild Photothermal/Chemodynamic/Starvation Therapy Through Self‐Reinforcing Cancer Energy Metabolism Regulation

AbstractPhotothermal therapy (PTT) has a great prospect in further improving tumor therapeutic outcomes, whereas its efficiency is restrained by low light penetration, excessive heat damage to normal tissues, up‐regulated heat shock proteins (HSPs), and limited effect of single treatment. Herein, an enzyme‐engineered coppery nanozyme based on dendritic mesoporous coppery carbon nanosphere as the cornerstone to load with glucose oxidase (GOx) followed by modification with hyaluronic acid is constructed. Density functional theory calculations indicate that the obtained coppery nanozyme exhibits peroxidase and glutathione oxidase mimicking activities to improve hydroxyl radicals (•OH) production. Furthermore, both the generation of •OH production and GOx‐induced energy supply blockade can reduce HSPs expression to enhance the mild PTT (η = 34.9 %) of coppery nanozyme upon the irradiation of 1064 nm laser, and in turn, accelerate the catalytic processes of coppery nanozyme for more generation of •OH. Last but not least, the introduction of copper can induce lipoylated protein dihydrolipoamide S‐acetyltransferase aggregation to cause cellular cuproptosis. Due to the synergy of multiple therapies, the tumor inhibition rate can reach 93.4%. Overall, this work provides an effective strategy for potential tumor treatment on the basis of synergistic therapies.

Synergistic effects of Fe-based nanomaterial catalyst on humic substances formation and microplastics mitigation during sewage sludge composting

In this study, a novel Fe-based nanomaterial catalyst (Fe0/FeS) was synthesized via a self-heating process and employed to explore its impact on the formation of humic substances and the mitigation of microplastics. The results reveal that Fe0/FeS exhibited a significant increase in humic acid content (71.01 mg kg−1). Similarly, the formation of humic substances resulted in a higher humification index (4.91). Moreover, the addition of Fe0/FeS accelerated the degradation of microplastics (MPs), resulting in a lower concentration of MPs (9487 particles/kg) compared to the control experiments (22792 particles/kg). Fe0/FeS significantly increased the abundance of medium-sized MPs (50–200 μm) and reduced the abundance of small-sized (10–50 μm) and large-sized MPs (>1000 μm). These results can be attributed to the Fe0/FeS regulating the ▪OH production and specific microorganisms to promote humic substance formation and the degradation of MPs. This study proposes a feasible strategy to improve composting characteristics and reduce contaminants.

Effect of long-term straw return on organic matter transformation by hydroxyl radical during paddy soil oxygenation

The generation of hydroxyl radicals (OH) mediated by Fe(II) has drawn increasing amounts of attention due to its significant role in the transformation of soil organic carbon (SOM) during redox fluctuations in paddy soil. This study further examined the effect of long-term (since 1984) straw return on Fe(II) on driving OH formation and SOM transformation upon paddy soils oxygenation. We found that long-term straw return could inhibit the OH and CO2 production in abiotic processes. The OH production decreased from 190.4 to 133.4 µM as the straw return amount increased from 0 to 19.16 t·hm−2·year−1. Moreover, 14.7–38.6 % of the CO2 production was associated with OH during oxygenation. By combining radical quenching and OM extraction, we determined that straw return could increase O2 reduction to H2O2 through a two-electron transfer pathway. Based on chemical extraction, Mössbauer spectra and multilinear regression model, we demonstrated that straw return resulted in more active Fe(II) species that controls the OH production. The results of 3DEEMs and FT-ICR MS showed that oxidative transformation can be accomplished by the introduction of OH to aromatic structures or olefins through ring opening and hydroxylation mechanisms. And OM at high straw return concentrations was likely oxidized by OH into bioavailable aliphatic compounds. Therefore, this study highlights the underappreciating effects of long-term straw return on Fe(II) oxidation in driving OH generation and SOM transformation in paddy soil redox fluctuation events.

Unprecedented sulfenic acid-dependent hydroxyl radical production and DNA damage by N-heterocyclic thiols and H2O2

The decomposition of H2O2 to produce the highly-reactive hydroxyl radical (•OH) is one of most well-known pathways to generate •OH, which can be readily activated by transition metal ions and haloquinones, but rarely by N-heterocyclic thiol compounds. Here we found, unexpectedly, that DNA oxidative damage can be induced by H2O2 together with 2-mercaptopyridine (PySH), a typical N-heterocyclic thiol compound widely-used in industry, agriculture, medicine and organic synthesis, which was found to be mainly due to production of •OH independent of transition metal ions. 2,2′-Dithiodipyridine, pyridine-2-sulfenic acid (PySOH), pyridine-2-sulfinic acid and pyridine-2-sulfonic acid were step-wisely produced during the reaction of PySH/H2O2, and the source and origin of the oxygen atoms inserted into these intermediates and products were found to be from H2O2 by oxygen-18 isotope labeling technique coupled with ESI-Q-TOF-MS analysis. More importantly, among all the transient intermediates, PySOH was found to be the key one directly responsible for •OH production from PySH/H2O2. Analogous results were observed with several PySH derivatives. This is the first report on an unprecedented sulfenic acid-dependent •OH production from the activation of H2O2 by N-heterocyclic thiol compounds, which may have important chemical, biological and biomedical implications for future study of these widely-used compounds.

Coordinated carbon dots-Fe featuring synergistically enhanced peroxidase-like activity at neutral pH for specific and background-free detection of dichlorvos

Nanozyme-based assays present favorable prospects in sensitive determination of pesticides in food samples yet are constrained with little or even no catalytic activities at neutral pH, lack of selectivity, and interference by sample color. Here, a facile and novel photothermal system for rapid, specific, sensitive, and background-free detection of dichlorvos was developed based on peroxidase-like activity of coordinated carbon dots-Fe (CDs-Fe). CDs-Fe was prepared and fabricated based on the redox and coordination chemistry between CDs and Fe species. Catalytic mechanism investigations illustrate that CDs-Fe with outstanding peroxidase-like activity at neutral pH comes from the synergistic effect of •OH production and electron transfer process. More interestingly, dichlorvos can specifically complex with CDs-Fe through electrostatic attraction and π-π stacking interactions, which then cement substrates affinity and improve electron transfer efficiency to enhance the catalytic activity. Oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB) presents photothermal effect by absorption of near-infrared (808 nm) laser-driven light, which eliminates the color interference from real samples. Accordingly, a background-free photothermal strategy was established. Furthermore, a portable hydrogel kit was fabricated by embedding CDs-Fe and TMB into agarose hydrogel for on-site rapid detection of dichlorvos. A good relationship was observed in the range of 5.00–650 μg L−1 with a satisfactory detection limit at 4.85 μg L−1, and a good recovery (90.56–107.0 %) with excellent anti-interference capacity was achieved for real sample analysis. The work presents a novel nanozyme enhancement strategy for specific and background-free detecting dichlorvos in food samples.

Field Quantification of Hydroxyl Radicals by Flow-Injection Chemiluminescence Analysis with a Portable Device.

Hydroxyl radical (•OH) is a powerful oxidant abundantly found in nature and plays a central role in numerous environmental processes. On-site detection of •OH is highly desirable for real-time assessments of •OH-centered processes and yet is restrained by a lack of an analysis system suitable for field applications. Here, we report the development of a flow-injection chemiluminescence analysis (FIA-CL) system for the continuous field detection of •OH. The system is based on the reaction of •OH with phthalhydrazide to generate 5-hydroxy-2,3-dihydro-1,4-phthalazinedione, which emits chemiluminescence (CL) when oxidatively activated by H2O2 and Cu3+. The FIA-CL system was successfully validated using the Fenton reaction as a standard •OH source. Unlike traditional absorbance- or fluorescence-based methods, CL detection could minimize interference from an environmental medium (e.g., organic matter), therefore attaining highly sensitive •OH detection (limits of detection and quantification = 0.035 and 0.12 nM, respectively). The broad applications of FIA-CL were illustrated for on-site 24 h detection of •OH produced from photochemical processes in lake water and air, where the temporal variations on •OH productions (1.0-12.2 nM in water and 1.5-37.1 × 107 cm-3 in air) agreed well with sunlight photon flux. Further, the FIA-CL system enabled field 24 h field analysis of •OH productions from the oxidation of reduced substances triggered by tidal fluctuations in coastal soils. The superior analytical capability of the FIA-CL system opens new opportunities for monitoring •OH dynamics under field conditions.

Observations of HONO and its precursors between urban and its surrounding agricultural fields: The vertical transports, sources and contribution to OH

The insufficient study on vertical observations of main atmospheric reactive nitrogen oxides (NO2 and HONO) posed a great challenge to evaluate their intertransport between urban and agricultural areas, and to further learn the atmospheric nitrogen chemistry and the atmospheric oxidation capacity at high altitudes. A stereoscopic measurement campaign (satellite remote sensing, hyperspectral unmanned aerial vehicle (UAV) remote sensing and MAX-DOAS observation) was performed in a typical inland city Hefei and its surrounding agricultural fields from June to October 2022. Average aerosol vertical profiles exhibited a Gaussian shape above 100 m with maximum values of 0.67 km−1 and 0.55 km−1 at 300–400 m layer at Anhui University (AHU) and Changfeng (CF), respectively. The distinct layered structure was mainly attributed to regional transport. Average H2O and NO2 vertical profiles all showed a Gaussian shape and an exponential shape at AHU and CF, respectively. Moreover, the diurnal evolution of H2O profiles performed one peak and bi-peak patterns at AHU and CF, respectively, whereas the diurnal evolution of NO2 at two stations all exhibited bi-peak patterns attributed to vehicle emissions. Average HONO vertical profiles showed an exponential shape and a Gaussian shape at AHU and CF, respectively. Higher HONO (> 0.05 ppb) above 1.0 km at 14:00–16:00 was observed at CF. The transport flux analysis showed that the northern transport flux always larger than southern transport flux for aerosol and H2O. The maximum northern transport fluxes appeared at 300 m and surface for aerosol and H2O, respectively. It indicated that surrounding agricultural fields was an important source of atmospheric H2O of city. The southern transport flux was larger than northern transport flux for NO2, with a maximum net transport flux of 9.20 ppb m s−1 at 100 m. It demonstrated that NO2 transported from urban areas was an important source of NO2 in agricultural fields. For HONO, the southern transport flux was larger than northern transport flux under 100 m, whereas it was opposite above 100 m. It indicated that the HONO distributed at high altitudes at agricultural fields had potential to enhance the atmospheric oxidation capacity of urban area. The net horizontal transport fluxes of HONO of our defined cropland were 5.25 μg m−2 s−1 and -3.65 μg m−2 s−1 during non-fertilization and fertilization periods, respectively. It indicated that the cropland could obviously export HONO to surrounding atmosphere during the fertilization period. Deducing the contribution of direct emission, heterogeneous process was a major source of HONO at urban and agricultural areas. The average surface conversion rate of NO2-to-HONO (CHONO) was 0.01467 h−1, and this value decreased with the increase of height at urban station. While average surface CHONO was 0.0322 h−1 at agricultural fields, which was ~1.2–2.8 times higher than that at urban area. The CHONO at agricultural fields significantly increased with the increase of height. The average CHONO at 1.0 km was ~2.0–3.6 times higher than that at surface. That suggested that the heterogeneous process was the main HONO source at high altitudes at CF, and this process obviously correlated with aerosol and H2O. The higher OH production from HONO (P(OH)HONO) occurred at 0–200 m and 100–400 m with averaged values of 0.31 ppb h−1 and 0.39 ppb h−1 at AHU and CF, respectively. The high P(OH)HONO above 1.0 km at CF from September to October was strongly correlated with high O3 (> 80 ppb). This study emphasized the importance of the stereoscopic of HONO on the analysis of its distribution, evolution, source and atmospheric oxidizing contribution.

Coarse particles compensate for missing daytime sources of nitrous acid and enhance atmospheric oxidation capacity in a coastal atmosphere

Large missing sources of daytime atmospheric nitrous acid (HONO), a vital source of hydroxyl radicals (OH) through its photolysis, frequently exist in global coastal regions. In this study, ambient HONO and relevant species were measured at a coastal site in the Pearl River Delta (PRD), China, during October 2019. Relatively high concentrations (0.32 ± 0.19 ppbv) and daytime peaks at approximately 13:00 of HONO were observed, and HONO photolysis was found to be the dominant (55.5 %) source of the primary OH production. A budget analysis of HONO based on traditional sources suggested large unknown sources during the daytime (66.4 %), which had a significant correlation with the mass of coarse particles (PM2.5–10) and photolysis frequency (J(NO2)). When incorporating photolysis of the abundant nitrate measured in coarse particles with a reasonable enhancement factor relative to fine particles due to favorable aerosol conditions, the missing daytime sources of HONO could be fully compensated by coarse particles serving as the largest source at this coastal site. Our study revealed great potential of coarse particles as a strong daytime HONO source, which has been ignored before but can efficiently promote NOx recycling and thus significantly enhance atmospheric oxidation capacity.

Climate and Tropospheric Oxidizing Capacity

The hydroxyl radical (OH) largely controls the tropospheric self-cleansing capacity by reacting with gases harmful to the environment and human health. OH concentrations are determined locally by competing production and loss processes. Lacking strong observational constraints, models differ in how they balance these processes, such that the sign of past and future OH changes is uncertain. In a warmer climate, OH production will increase due to its water vapor dependence, partially offset by faster OH-methane loss. Weather-sensitive emissions will also likely increase, although their net impact on global mean OH depends on the balance between source (nitrogen oxides) and sink (reactive carbon) gases. Lightning activity increases OH, but its response to climate warming is of uncertain sign. To enable confident projections of OH, we recommend efforts to reduce uncertainties in kinetic reactions, in measured and modeled OH, in proxies for past OH concentrations, and in source and sink gas emissions. ▪OH is strongly modulated by internal climate variability despite its lifetime of a few seconds at most, with implications for interpreting trends in methane.▪Improved kinetic constraints on key reactions would strengthen confidence in regional and global OH budgets, and in the response of OH to climate change.▪Future OH changes will depend on uncertain and compensating processes involving weather-sensitive chemistry and emissions, plus human choices.▪Technological solutions to climate change will likely impact tropospheric oxidizing capacity and merit further study prior to implementation.

Efficient hydroxyl radical production and sulfanilamide degradation during oxygenation of microbially reduced metal–organic frameworks

Incubation of iron-reducing bacteria with Fe(III) could generate •OH to decompose organic pollutants under redox fluctuation conditions. However, the Fe(III)/Fe(II) transformation efficiency and therefore yields of •OH production in systems using Fe(III)-bearing minerals as respiration substrate of bacteria is unsatisfying. Here, we showed that different iron- and iron-copper-based metal–organic frameworks (Fe-MOFs and FeCu-MOFs) can mediate electron transfer from Shewanella oneidensis MR-1 to O2 through their Fe(III)/Fe(II) cycling during anoxic–oxic transition, resulting in generation of reactive oxygen species including •O2–, H2O2 and •OH. While 3 g/L of MIL-101(Fe) demonstrated faster Fe(III)/Fe(II) cycling, better yields of •OH production (69.0 μmol/mmol Fe(II) oxidation) and sulfanilamide removal (81.5 % in 24 h) than iron-bearing minerals and the rest two Fe-MOFs (MIL-53(Fe) and MIL-88B(Fe)), Fe0.75Cu0.25-B surpassed the performance of MIL-101(Fe) and other FeCu-MOFs with different Fe/Cu ratios, which might be attributed to its larger surface area, higher amounts of associated Fe(II), and synergistic effects between Fe and Cu species. Moreover, both MIL-101(Fe) and Fe0.75Cu0.25-B maintained structure stability and persistent catalytic activity during four continuous redox cycles in 48 h, the •OH production and sulfanilamide degradation of which exceeded those of one-time operation in the same duration. This study revealed the efficacy of combining bacteria and MOFs for •OH production, and provided promising alternatives for oxidative degradation of contaminants.

Induction of Extracellular Hydroxyl Radicals Production in the White-Rot Fungus Pleurotus eryngii for Dyes Degradation: An Advanced Bio-oxidation Process.

Among pollution remediation technologies, advanced oxidation processes (AOPs) are genuinely efficient since they are based on the production of strong, non-selective oxidants, mainly hydroxyl radicals (·OH), by a set of physicochemical methods. The biological counterparts of AOPs, which may be referred to as advanced bio-oxidation processes (ABOPs), have begun to be investigated since the mechanisms of induction of ·OH production in fungi are known. To contribute to the development of ABOPs, advanced oxidation of a wide number of dyes by the white-rot fungus Pleurotus eryngii, via a quinone redox cycling (QRC) process based on Fenton's reagent formation, has been described for the first time. The fungus was incubated with 2,6-dimethoxy-1,4-benzoquinone (DBQ) and Fe3+-oxalate, with and without Mn2+, leading to different ·OH production rates, around twice higher with Mn2+. Thanks to this process, the degradative capacity of the fungus increased, not only oxidising dyes it was not otherwise able to, but also increasing the decolorization rate of 20 dyes by more than 7 times in Mn2+ incubations. In terms of process efficacy, it is noteworthy that with Mn2+ the degradation of the dyes reached values of 90-100% in 2-4 h, which are like those described in some AOPs based on the Fenton reaction.