OH Production Rates Research Articles

Single-Molecule Imaging of Reactive Oxygen Species on a Semiconductor Nano-Heterostructure for Understanding Photocatalytic Heterogeneity in Aqueous.

We constructed a single-molecule fluorescence imaging technique to monitor the spatiotemporal distribution of the hydroxyl radical (•OH) on TiO2-attached multiwalled carbon nanotubes (TiO2-MWCNTs) in aqueous. We found the heterogeneous distribution of •OH is closely related to the composition and heterostructure of the catalysts. The dynamic •OH production rate was evaluated by counting the single-molecule fluorescent bursts. We further confirmed the production of •OH on TiO2-MWCNTs mainly occurred via electron reduction during the aqueous photocatalytic process. Our study reveals the mechanism of reactive oxygen species involved photocatalytic reaction and guides the design of advanced semiconductor photocatalysts.

Seasonal dependency of the atmospheric oxidizing capacity of the marine boundary layer of Bermuda

In this study, we investigate the atmospheric oxidation capacity in the marine boundary layer during two measurement campaigns in spring and summer 2019 at the Tudor Hill Marine Atmospheric Observatory, Bermuda. Measured species included non-methane hydrocarbons (NMHCs), HONO, HNO3, particulate matter, particulate nitrates, NO, NO2, O3, in addition to the meteorological parameters. Measured concentrations of all species were generally higher in spring than in summer. During the spring and summer, OH initiation sources made 61% and 42% of the total OH production rate (POH) during the daytime, respectively. The higher levels of NMHCs and OH production from ozone photolysis lead to a higher oxidation rate of NMHCs in the spring compared to summer. However, the low NO in the spring and summer leads to inefficient recycling of RO2 and HO2 to OH, with HO2 reaction with NO accounting for only 22% and 42% of POH during spring and summer. Sensitivity analysis suggests that OH reactivity in the MBL can be potentially enhanced by an oceanic source rather than a secondary oxidation product. Including halogen monoxides, BrO and IO were found to decrease HO2 by ∼14 and 18% during spring and summer, respectively, with marginal impact on OH due to the higher loss by aerosol uptake. The results demonstrate the complex multiphase HOx-Halogen chemistry and call for a more comprehensive multiphase investigation.

Prodigious Amounts of Hydrogen Oxides Generated by Corona Discharges on Tree Leaves

AbstractProdigious amounts of the hydroxyl radical (OH) are generated in the laboratory on tree leaves by corona discharges, which also occur on trees during thunderstorms. Production rates of OH and HO2 depend on the applied electric field generating the corona discharge, leaf dryness, and the presence of liquid water on the leaf. However, they are independent of leaf type and corona discharge polarity for a given corona ultraviolet (UV) flux. Production rates of OH, HO2, and O3 strongly correlate with corona UV flux. Although the contribution of corona‐produced OH to total global OH production is unlikely to be important, corona‐generated OH is likely a few orders of magnitude greater than oxidation by known processes in the vicinity of the affected leaves, potentially influencing atmospheric oxidation and tree and forest ecology.

Electrochemical treatment of waste activated sludge: Volume reduction mechanism and improvement possibilities

In this study, a PbO2 plate electrode was synthesized and optimized for the electrochemical treatment application of waste activated sludge from a municipal wastewater treatment. The sludge dewaterability and mass reduction with different electrolysis time and voltage were quantified to evaluate the treatment efficiency. The mechanism of cell breaking was studied by evaluating different electrochemical oxidation pathways. Results showed that the electrochemical treatment at a voltage of 25 V and electrolysis time of 120 min improved the dewaterability of the sludge by 35.9%, and the concentration of mixed liquor suspended solids (MLSS) was reduced by 33.7%. Using Scanning Electron Microscope (SEM) and Cell fluorescence staining experiments, the impact on the integrity of sludge cells was evaluated. Results showed that electrochemical process clearly destroyed the sludge cell structure and lead to the cell death. Further investigation revealed that hydroxyl radicals (·OH) and sulfate radicals (SO4·-) produced during the electrochemical treatment played a major role in the cell wall-breaking, while chloride ions (Cl-) in the electrolyte significantly enhanced the effect due to formation of chloride-related oxidants. The PbO2 electrode was modified by chemically reduced graphene oxide (RGO) to improve the ·OH production capacity. Results showed that the PbO2(0.05 RGO by wt.%) electrode had the highest ·OH production rate (81.7 μmol/(cm2·min)). The electrode improved the removal of MLSS and MLVSS by 11.3% and 11.5%, respectively. And the sludge dewatering and cell destruction were enhanced by 7% and 15.1%, respectively. Adding more NaCl was confirmed as an effective method to improve the electrochemical performance of sludge treatment mainly due to the higher content of active Cl- species formed.

Acid–base Homeostasis and Implications to the Phenotypic Behaviors of Cancer

Acid–base homeostasis is a fundamental property of living cells, and its persistent disruption in human cells can lead to a wide range of diseases. In this study, we conducted a computational modeling analysis of transcriptomic data of 4750 human tissue samples of 9 cancer types in The Cancer Genome Atlas (TCGA) database. Built on our previous study, we quantitatively estimated the average production rate of OH− by cytosolic Fenton reactions, which continuously disrupt the intracellular pH (pHi) homeostasis. Our predictions indicate that all or at least a subset of 43 reprogrammed metabolisms (RMs) are induced to produce net protons (H+) at comparable rates of Fenton reactions to keep the pHi stable. We then discovered that a number of well-known phenotypes of cancers, including increased growth rate, metastasis rate, and local immune cell composition, can be naturally explained in terms of the Fenton reaction level and the induced RMs. This study strongly suggests the possibility to have a unified framework for studies of cancer-inducing stressors, adaptive metabolic reprogramming, and cancerous behaviors. In addition, strong evidence is provided to demonstrate that a popular view that Na+/H+ exchangers along with lactic acid exporters and carbonic anhydrases are responsible for the intracellular alkalization and extracellular acidification in cancer may not be justified.

The Levels and Sources of Nitrous Acid (HONO) in Winter of Beijing and Sanmenxia

AbstractHONO concentrations in Beijing (BJ) and Sanmenxia (SMX) were simultaneously measured in winter with a duration of 1 month, and the sources and sinks of HONO in the two cities were comparably analyzed. BJ and SMX had different pollution characteristics. Direct vehicle emission made a contribution to observed HONO of about 28% in BJ, whereas it contributed to HONO only about 12% in SMX. Additionally, direct emission from coal combustion in SMX also made a significant contribution to atmospheric HONO, which could achieve to be 13%. In BJ, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 15% and 27%, respectively. In SMX, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 40% and 30%, respectively. Daytime NO2 heterogeneous conversion (including photo‐enhanced conversion) on the aerosol and ground surfaces was important in SMX. Daytime NO3− photolysis contributed 9% HONO in SMX and 4% in BJ. The primary OH production rates from photolysis of daytime HONO in both BJ and SMX were three orders of magnitude faster than those from photolysis of O3, revealing the dominant role of HONO in local atmospheric chemistry of the two cities in winter.

Enhancing the yield of H2O2 and bisphenol A degradation via a synergistic effect of photoelectric co-catalysis by using NPC/C3N4 electrode

This study reported a photoelectric co-catalyst system of jet-flow reactor for efficient mineralization of Bisphenol A (BPA), where H2O2 was photoelectro-generated in situ from O2 reduction on gas diffusion electrodes fabricated by nitrogen-doped porous carbon and graphitic carbon nitride (NPC/g-C3N4). Current density, aeration rate, amount of MoS2 and FeSO4 catalyst in the jet-flow reactor photoelectrocatalysis system for BPA removal were investigated. The NPC/g-C3N4 cathodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and the electrochemical workstation. The results show that at pH 7, the NPC/g–C3N4–(60%) has the highest rate of electrical generation hydrogen peroxide. When the pH rised, at pH values of 7, the cumulative of hydrogen peroxide increased, when the solution get slight alkaline, it was gradually decreased. Compared with the traditional electro-Fenton technology, the photoelectric method of co-catalysis has strong ·OH production rate and high oxidation ability. A possible mechanism for BPA degradation was oxidized by hydroxyl radical (·OH), resulting in the formation of shorter chain bisphenol A (BPA), which followed the same reaction cycle as BPA until it was mineralized. The removal rate of BPA can reach 100% within 20 min, the TOC removal rate up to 90%. This work provides new opinion into the development of a photoelectric collaborative system for H2O2 generation and the fast BPA degradation.

Atmospheric oxidizing capacity in autumn Beijing: Analysis of the O3 and PM2.5 episodes based on observation-based model

Atmospheric oxidizing capacity (AOC) is the fundamental driving factors of chemistry process (e.g., the formation of ozone (O3) and secondary organic aerosols (SOA)) in the troposphere. However, accurate quantification of AOC still remains uncertainty. In this study, a comprehensive field campaign was conducted during autumn 2019 in downtown of Beijing, where O3 and PM2.5 episodes had been experienced successively. The observation-based model (OBM) is used to quantify the AOC at O3 and PM2.5 episodes. The strong intensity of AOC is found at O3 and PM2.5 episodes, and hydroxyl radical (OH) is the dominating daytime oxidant for both episodes. The photolysis of O3 is main source of OH at O3 episode; the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) plays important role in OH formation at PM2.5 episode. The radicals loss routines vary according to precursor pollutants, resulting in different types of air pollution. O3 budgets and sensitivity analysis indicates that O3 production is transition regime (both VOC and NOx-limited) at O3 episode. The heterogeneous reaction of hydroperoxy radicals (HO2) on aerosol surfaces has significant influence on OH and O3 production rates. The HO2 uptake coefficient (γHO2) is the determining factor and required accurate measurement in real atmospheric environment. Our findings could provide the important bases for coordinated control of PM2.5 and O3 pollution.

LRO-LAMP Observations of the Preperihelion Coma of Comet C/2013 A1 (Siding Spring)

Abstract The Lyman-Alpha Mapping Project (LAMP) UV spectrograph on board the Lunar Reconnaissance Orbiter observed comet C/2013 A1 (Siding Spring) from lunar orbit at closest approach. On 2014 September 5, Siding Spring came within ∼0.89 au of the Earth–Moon system and provided an opportunity for LAMP to contribute to the broader campaign of observations. The comet coma was imaged during two consecutive orbits, approximately 2 hr apart. Coma emissions of atomic oxygen were resolved within LAMP observations at distances up to ∼1.4 × 106 km from the comet nucleus. We report an atomic production rate for the observed oxygen of 9.42 ± 0.22 × 1027 s−1. We additionally place upper limits on the column densities of candidate species including noble gases and primary transitions. Leveraging this, we place upper limits on the production of hydrogen and carbon of <3.59 × 1026 s−1 and <8.41 × 1025 s−1, respectively. Additionally, we derive OH and H2O production rates and estimate an upper limit on the production of CO. The H2O (8.17 ± 2.64 × 1027 s−1) and OH (7.53 ± 2.244 × 1027 s−1) production rates are found to be in general agreement with previous studies when production rates are derived utilizing oxygen observations, branching ratios, and empirical formulations. Similarly, the upper limit on the production of CO (<1.33 × 1028 s−1) is found to be in good agreement with previous studies (within ∼10%) when we utilize the upper limit on CO Fourth Positive group emissions.

A Study on the Formation Reactions and Conversion Mechanisms of HONO in the Atmosphere

This study was designed to identify major atmospheric HONO sources that trigger the accumulation of ozone by generating OH radicals through its photolysis. We measured HONO in the atmosphere using the PPDS-IC system and found that HONO concentration was 2.61 ± 1.91 ppb in the winter and 1.8 ± 0.76 ppb in the summer. Regardless of seasons, HONO concentration tended to be proportional to the NO2 level, and the HONO/NO2 ratio was greatly influenced by relative humidity. The conversion rate of HONO from NO2 was similar in winter and summer, but the variation of HONO in winter was larger than that of summer. Although the photolysis rate of HONO was lower in the winter, but the OH production rate was larger in the winter due to its higher concentrations observed. In addition to nighttime heterogeneous production with NO2, unknown sources played the very important role in the HONO budget, especially in the daytime and they should be resolved in future studies.

Mechanisms for hydroxyl radical production and arsenic removal in sulfur-vacancy greigite (Fe3S4)

Herein, we systematically investigated the mechanisms of OH production and arsenic (As(III)) oxidation induced by sulfur vacancy greigite (Fe3S4) under anoxic and oxic conditions. Reactive oxygen species analyses revealed that sulfur vacancy-rich Fe3S4 (SV-rich Fe3S4) activated molecular oxygen to produce hydrogen peroxide (H2O2) via a two-electron reduction pathway under oxic conditions. Subsequently, H2O2 was decomposed to OH via the Fenton reaction. Additionally, H2O was directly oxidized to OH by surface high-valent iron (Fe(IV)) resulting from the abundance of sulfur vacancies in Fe3S4 under anoxic/oxic conditions. These differential OH-generating mechanisms of Fe3S4 resulted in higher OH production of SV-rich Fe3S4 compared to sulfur vacancy-poor Fe3S4 (SV-poor Fe3S4). Moreover, the OH production rate of SV-rich Fe3S4 under oxic conditions (19.3 ± 1.0 μM•h−1) was 1.6 times greater than under anoxic conditions (11.8 ± 0.4 μM•h−1). As(III) removal experiments and X-ray photoelectron spectra (XPS) showed that both OH production pathways were favorable for As(III) oxidation, and a higher concentration of As(V) was immobilized on the surface of SV-rich Fe3S4 under oxic conditions. This study provides new insights concerning OH production and environmental pollutants removal mechanisms on surface defects of Fe3S4 under anoxic and oxic conditions.

Tight electrostatic regulation of the OH production rate from the photolysis of hydrogen peroxide adsorbed on surfaces

Recently, experimental and theoretical works have reported evidence indicating that photochemical processes may significantly be accelerated at heterogeneous interfaces, although a complete understanding of the phenomenon is still lacking. We have carried out a theoretical study of interface and surface effects on the photochemistry of hydrogen peroxide (H2O2) using high-level ab initio methods and a variety of models. Hydrogen peroxide is an important oxidant that decomposes in the presence of light, forming two OH radicals. This elementary photochemical process has broad interest and is used in many practical applications. Our calculations show that it can drastically be affected by heterogeneous interfaces. Thus, compared to gas phase, the photochemistry of H2O2 appears to be slowed on the surface of apolar or low-polar surfaces and, in contrast, hugely accelerated on ionic surfaces or the surface of aqueous electrolytes. We give particular attention to the case of the neat air-water interface. The calculated photolysis rate is similar to the gas phase, which stems from the compensation of two opposite effects, the blue shift of the n→σ* absorption band and the increase of the absorption intensity. Nevertheless, due to the high affinity of H2O2 for the air-water interface, the predicted OH production rate is up to five to six orders of magnitude larger. Overall, our results show that the photochemistry of H2O2 in heterogeneous environments is greatly modulated by the nature of the surface, and this finding opens interesting new perspectives for technological and biomedical applications, and possibly in various atmospheres.

Comparative observation of atmospheric nitrous acid (HONO) in Xi'an and Xianyang located in the GuanZhong basin of western China

HONO is an important component of reactive nitrogen (Nr) and precursors of OH radical. However, the source and removal of HONO are not clear. Here, measurements of HONO (May 18–31, 2018) were conducted in Xi'an and Xianyang simultaneously for the first time. The relationship between HONO and other Nr (such as NO and NO2) in two cities was analyzed. The mixing ratio of HONO in Xi'an was 1.2 ± 0.8 ppbv, and that in Xianyang was 1.2 ± 1.1 ppbv. The nighttime HONO mixing ratio was higher in Xianyang, while the daytime HONO was higher in Xi'an. Compared with the contribution from heterogeneous process of NO2, direct emissions and homogeneous processes (NO + OH) were less important for nocturnal HONO formation in these two cities. The relative contribution of heterogeneous process in Xianyang was more important than that in Xi'an. The reaction of NO2 upon aerosols surface was identified as an important source of HONO for two sites. The conversion of NO2 on the other surfaces might attend the heterogeneous formation of HONO in Xianyang site. Daytime HONO budget analysis indicated that there was an additional unknown formation process of HONO at two sites. The net OH production rate from HONO (from 08:00 to 17:00) was 1.6 × 107 and 1.3 × 107 molecule/(cm3 s) for Xian and Xianyang, 5.2 and 3.5 times higher than from O3 photolysis. Besides, a dust storm appeared during this observation period, and the impact of local emission and transport processes was separately analyzed. The sources, characteristics, and effects of HONO identified in this study laid a foundation for further research on HONO and air pollution in the Guanzhong area.

Detection of OH 18 cm Emission from Comet C/2020 F3 NEOWISE Using the Arecibo Telescope

Abstract We report the detection of emission from the OH 18 cm Λ-doublet transitions toward Comet C/2020 F3 NEOWISE using the Arecibo Telescope. The antenna temperatures are 113 ± 3 mK for the 1667 MHz line and 57 ± 3 mK for the 1665 MHz line. The beam-averaged OH column density (centered on the comet nucleus) derived from the 1667 transition is N OH = (1.11 ± 0.06) × 1013 cm−2. We implemented the Haser model to derive an OH production rate. The estimated OH production rate using the 1667 transition is Q OH = (3.6 ± 0.6) × 1028 s−1, a factor of 2.4 lower than optically derived values for the same observing day, the difference of which is likely explained by quenching.

Atmospheric nitrous acid (HONO) in an alternate process of haze pollution and ozone pollution in urban Beijing in summertime: Variations, sources and contribution to atmospheric photochemistry

Nitrous acid (HONO), as a key reservoir of hydroxyl radical (OH), plays a significant role in atmospheric chemistry. To study the sources and atmospheric influence of HONO, continuous observations of HONO and relevant air pollutants were performed from June to July 2019 at an urban site in Beijing. A comparative study on the ambient levels, diurnal variation, the sources in daytime and nighttime, and the formation mechanisms were investigated for a haze pollution period (Period I) and an ozone pollution period (Period II). The average hourly HONO concentrations during Period I, Period II, and the whole observation period, were 0.58 ± 0.23, 0.54 ± 0.19 and 0.44 ± 0.24 ppb, respectively. The emission from vehicle exhaust was an important source of nocturnal HONO formation. During the nighttime, compared with the homogeneous reaction of NO with OH, the heterogeneous conversion from NO2 was the dominant pathway for HONO formation. The heterogeneous conversion frequency was 0.0075 h−1 during Period I, higher than that during Period II (0.0028 h−1), suggesting a higher conversion potential to HONO formation during the haze episode. Based on the analysis of HONO budget, it was found that the daytime unknown source Punknown during Period II was higher than that during Period I. Correlation analysis implied that the photo-enhanced NO2 conversion on the aerosol surface might be a potential source for daytime HONO. Without HONO constraint, the Observation-Based Model (OBM) would largely underestimate the averaged daytime atmospheric oxidative capacity (24%), OH production rate (57%), and net O3 production rate (20%). The study results further demonstrated the necessity for clarifying the formation mechanism of HONO to improve the understanding of the influence of HONO to atmospheric chemical processes.

Measurement of the density and rotational temperature of OH in a saturated water vapor slot-excited microwave plasma

OH density and rotational temperature were measured in a saturated water vapor slot-excited microwave plasma using spatio-temporally resolved laser-induced fluorescence. The microwave power was 20–100 W under continuous wave mode, whereas 40–200 W peak under pulse-modulated mode (30% duty cycle, 100 Hz). The water vapor pressure was 2.3 kPa. An approximately 2 mm thick flat-shaped plasma was generated on the surface of a slot antenna. The OH density and rotational temperature in the plasma ranged from 1 × 1014 cm−3 to 1 × 1015 cm−3 and from 1100 K to 3000 K, respectively. OH was produced via various routes originating from electron collisions (e + H2O) and was primarily lost through recombination (OH+OH → H2O+O) and diffusion. The production rate (k p ) of OH per H2O molecule, which was calculated based on a simplified reaction model using the measured OH density and temperature, showed a relation of , where P represents the microwave power. This relationship implies a two-step production process of OH via the vibrational excitation of H2O. Although the OH density increased with increasing microwave power, the density became saturated at high power values.

Vertical distributions of wintertime atmospheric nitrogenous compounds and the corresponding OH radicals production in Leshan, southwest China

Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations were operated from 02 to 21 December 2018 in Leshan, southwest China, to measure HONO, NO2 and aerosol extinction vertical distributions, and these were the first MAX-DOAS measurement results in Sichuan Basin. During the measurement period, characteristic ranges for surface concentration were found to be 0.26–4.58 km−1 and averaged at 0.93 km−1 for aerosol extinction, 0.49 to 35.2 ppb and averaged at 4.57 ppb for NO2 and 0.03 to 7.38 ppb and averaged at 1.05 ppb for HONO. Moreover, vertical profiles of aerosol, NO2 and HONO were retrieved from MAX-DOAS measurements using the Heidelberg Profile (HEIPRO) algorithm. By analysing the vertical gradients of pollutants and meteorological information, we found that aerosol and HONO are strongly localised, while NO2 is mainly transmitted from the north direction (city center direction). Nitrogen oxides such as HONO and NO2 are important for the production of hydroxyl radical (OH) and oxidative capacity in the troposphere. In this study, the averaged value of OH production rate from HONO is about 0.63 ppb/hr and maximum value of ratio between OH production from HONO and from (HONO+O3) is > 93% before12:00 in Leshan. In addition, combustion emission contributes to 26% for the source of HONO in Leshan, and we found that more NO2 being converted to HONO under the conditions with high aerosol extinction coefficient and high relative humidity is also a dominant factor for the secondary produce of HONO.

Evidence for Strong HONO Emission from Fertilized Agricultural Fields and its Remarkable Impact on Regional O3 Pollution in the Summer North China Plain

Summertime HONO concentrations were synchronously measured at two (agricultural and nonagricultural) sites in the North China Plain (NCP). Daytime HONO (1.4 ± 0.6 ppbv) and HONO/NO2 ((12 ± 8)%) over the agricultural field after fertilization were found to be remarkably higher than those before fertilization, implying strong HONO emission from the fertilized fields. Synchronous enhancements of HONO and O3 after fertilization at both sites suggested that the emitted HONO accelerated the local and the regional O3 pollution. HONO budget analysis further revealed that its emission was significantly enhanced after fertilization. Soil HONO emission flux and its uncertainty were estimated and discussed. The estimated emission flux exhibited a distinct diurnal variation with a noontime maximum. The net OH production rate from HONO photolysis greatly exceeded that from O3 photolysis over the agricultural field, and their maximum ratio of 4.7 was obtained after fertilization. We provide field evidence that fertilized fields in the NCP act as a strong HONO source, which accelerates daytime photochemistry, leading to an increase of regional photo-oxidants such as O3. Considering the severe O3 pollution in the summer NCP and that the large area of the agricultural field is regularly treated with high fertilization amount in this region, HONO emission should be taken into account in the regional air quality deterioration.

Role of the dew water on the ground surface in HONO distribution: a case measurement in Melpitz

Abstract. To characterize the role of dew water for the ground surface HONO distribution, nitrous acid (HONO) measurements with a Monitor for AeRosols and Gases in ambient Air (MARGA) and a LOng Path Absorption Photometer (LOPAP) instrument were performed at the Leibniz Institute for Tropospheric Research (TROPOS) research site in Melpitz, Germany, from 19 to 29 April 2018. The dew water was also collected and analyzed from 8 to 14 May 2019 using a glass sampler. The high time resolution of HONO measurements showed characteristic diurnal variations that revealed that (i) vehicle emissions are a minor source of HONO at Melpitz station; (ii) the heterogeneous conversion of NO2 to HONO on the ground surface dominates HONO production at night; (iii) there is significant nighttime loss of HONO with a sink strength of 0.16±0.12 ppbv h−1; and (iv) dew water with mean NO2- of 7.91±2.14 µg m−2 could serve as a temporary HONO source in the morning when the dew droplets evaporate. The nocturnal observations of HONO and NO2 allowed the direct evaluation of the ground uptake coefficients for these species at night: γNO2→HONO=2.4×10-7 to 3.5×10-6, γHONO,ground=1.7×10-5 to 2.8×10-4. A chemical model demonstrated that HONO deposition to the ground surface at night was 90 %–100 % of the calculated unknown HONO source in the morning. These results suggest that dew water on the ground surface was controlling the temporal HONO distribution rather than straightforward NO2–HONO conversion. This can strongly enhance the OH reactivity throughout the morning time or in other planted areas that provide a large amount of ground surface based on the OH production rate calculation.

Phanerochaete chrysosporium-driven quinone redox cycling promotes degradation of imidacloprid

This study systematically investigated the advanced oxidation processes driven by the white-rot fungus (WRF) Phanerochaete chrysosporium in the removal of the neonicotinoid pesticide imidacloprid (IMI). The quinone redox cycling driven by P. chrysosporium promotes the degradation of IMI in presence of Mn2+ and Fe (III)-oxalate. Results showed that the degradation efficiency varied with the type of quinine mediator, and gallic acid (GA) was a more effective mediator than 1,4-benzoquinone (BQ). The removal rate of IMI was increased by 1.8-fold in the presence of 100 μM of Mn2+ compared with that of the system without Mn2+. The addition of oxalic acid and EDTA promoted the degradation of IMI, and the effect of oxalic acid was more pronounced at the later stage (day 5 and day 6); the optimal Fe3+/oxalate ratio was 1:3. Time-course experiments revealed the maximum removal rates of IMI were 97.37%, 82.0% and 73.52% at the initial IMI concentration of 10, 20, and 30 mg/L, respectively, in the presence of 100 μM Mn2+, 100 μM Fe3+-300 μM of oxalate and 500 μM gallic acid. Under quinone redox cycling conditions, the good correlation between ·OH production rates and the enzymes activity was concluded, the quinines redox cycles promote enzyme activity, as well as the rate of ·OH production. Results from this study indicated the GA mediator-based system using P. chrysosporium offers a new method to advance the bio-oxidation process owing to its simple culture system, low-cost precursors, unique fungi, and degradation stability.