Production Of OH Radicals Research Articles

Investigation of ROS-Driven Cytotoxic Mechanisms in WO3:Ag Heterostructures Supported on Carbon Against Bladder Cancer

Bladder cancer presents a significant health challenge due to its high malignancy and rising incidence rates. Silver-based materials are well-known for their cytotoxic effects on various cell types. This study not only aimed to synthesize and characterize carbon-supported WO3:Ag heterostructures but also to evaluate their biological and physicochemical properties. The material was synthesized through the synergistic thermal decomposition of α-Ag2WO4 dispersed in chitosan, followed by WO3:Ag heterostructure formation on a carbon support, yielding samples with varying α-Ag2WO4 concentrations (SC, SC1, SC2, and SC4, for 0, 10, 20 and 40% of α-Ag2WO4 for chitosan). Characterization confirmed the successful formation of carbon-supported heterostructures with controlled ionic release and enhanced ROS generation. In vitro assays were conducted to assess the viability of non-tumor (3T3 fibroblasts) and tumor (bladder carcinoma MB49) cells using MTT salt and neutral red dye. Additional analyses included autophagy detection by correlating data from viability assays, nitric oxide and ROS quantification using the Griess reaction and fluorescent probes, and Caspase-3 activity measured with a fluorescent antibody. The results indicated that SC1 and SC2 samples were more effective against both cell types, with SC2 showing heightened effectiveness against the tumor lineage by inducing greater oxidative stress in MB49 cells compared to 3T3 fibroblasts. Additionally, the materials exhibited low ionic release (<0.01%), reducing potential adverse effects. Mechanistic analysis showed that the carbon support and synergistic interactions between WO₃ and Ag modulated ⦁OH radical production, even without light, enhancing the material's cytotoxic efficiency. These findings highlight the therapeutic potential of WO₃:Ag heterostructures as a safe and effective approach for treating aggressive cancers like bladder carcinoma, emphasizing the importance of further development in advanced biofunctional materials. This study also highlights the therapeutic potential of carbon-supported WO3:Ag heterostructures in bladder cancer treatment and underscores the importance of continued research in the development of novel anticancer strategies.

Insights into reaction mechanisms: Water’s role in enhancing in-situ hydrogen production from methane conversion in sandstone

In-situ conversion of subsurface hydrocarbons via electromagnetic (EM) heating has emerged as a promising technology for producing carbon-zero, affordable hydrogen (H2) production directly from natural gas reservoirs. However, the reaction pathways and role of water as an additional hydrogen donor in EM-assisted methane-to-hydrogen (CH4-to-H2) conversion are poorly understood. Herein, we employ a combination of lab-scale EM-heating experiments and reaction modeling analyses to unravel the reaction pathways and elucidate water’s role in enhancing hydrogen production. The labelled hydrogen isotope of deuterium oxide (D2O) is used to trace the sources of hydrogen. The results show that water significantly boosts hydrogen yield via coke gasification at around 400 °C and steam methane reforming (SMR) reaction at over 600 °C in the presence of sandstone. Water-gas shift reaction exhibits a minor impact on this enhancement. Reaction mechanism analyses reveal that the involvement of water can initiate auto-catalytic loop reactions with methane, which not only generates additional hydrogen but also produces OH radicals that enhance the reactants’ reactivity. This work provides crucial insights into the reaction mechanisms involved in water-carbon-methane interactions and underscores water’s potential as a hydrogen donor for in-situ hydrogen production from natural gas reservoirs. It also addresses the challenges related to carbon deposition and in-situ catalyst regeneration during EM heating, thus derisking this technology and laying a foundation for future pilots.

Degradation of ciprofloxacin by hydrogen peroxide activated with pyrite under simulated sunlight

Ciprofloxacin (CIP) residues in the environment pose risks to both human health and ecosystems. In this study, we explored the effect of hydrogen peroxide (H2O2) on CIP degradation, activated by pyrite (FeS2) under simulated sunlight. XRD, XRF, EDS, XSP, DRS, and PL tests confirmed the high purity of FeS2 and its photocatalytic properties. With [CIP] = 30 μM, [FeS2] = 0.2 g/L, [H2O2] = 0.2 mM, CIP removal reached 87.6 %. The removal rate of TOC reached 55.3 % after 60 min of light exposure, and hydroxyl radicals (OH) contributed 72.7 % to the process. H2O2 utilization was 67.5 %, and the system operated effectively across a pH range of 2.00 to 8.00. CIP removal in river water reached 87.9 % after 3 h of light exposure, though the degradation was slower than in ultrapure water. Cl−, SO42−, and NO3− had little effect on degradation, whereas H2PO4−, CO32−, and HCO3− significantly inhibited the process as their concentrations increased. In livestock wastewater, the simulated sunlight-FeS2/H2O2 system was less effective, but after diluting the wastewater 100 times, CIP removal reached 87.6 % after 60 min. The degraded solutions showed no significant toxicity. These findings suggest that FeS2, combined with simulated sunlight, can effectively catalyze low concentrations of H2O2 to produce OH radicals, removing antibiotics from livestock wastewater.

Stage-wise kinetic analysis of ammonia addition effects on two-stage ignition in dimethyl ether

Abstract Ammonia (NH3) has gained considerable attention as a promising carbon-free hydrogen carrier fuel for internal combustion engines, but its direct use in compression-ignition engines presents challenges, often requiring high-reactivity fuels to ignite the premixed NH3/air mixture and initiate combustion. This study focuses on the ignition process of binary NH3 and dimethyl ether (DME) mixtures, as DME is a carbon-neutral, high-reactivity fuel. A key novelty of this paper is the comparison of the ignition processes of DME and NH3/DME mixtures from a temporal, process-oriented perspective, analyzing chemical kinetics across distinct ignition phases rather than focusing solely on instantaneous reactions at discrete time points. The stage-wise analysis reveals that NH3 has minimal impact on the control mechanism governing the two-stage ignition process of DME. Specifically, DME still largely depends on OH radical proliferation during low-temperature oxidation (LTO), which releases heat as the reaction progresses. As the temperature increases, LTO branching pathways gradually shift to chain-propagation pathways, reducing overall reaction activity. The reactivity and temperature rise rate of the system are then governed by the H2O2 loop mechanism before thermal ignition. However, ammonia significantly extends the ignition delay of DME by competing with OH radicals, which are critical for DME oxidation, thus inhibiting ignition. As the ignition reaction proceeds, ammonia kinetics become more involved. For example, nitrogen-containing species from NH3 oxidation, such as NO, NO2, and NH2, react with CH3OCH2 to form CH3OCHO, reducing the flux through the LTO pathway of DME. While ammonia reaction pathways also produce OH radicals, this occurs at the expense of HO2 and H radicals, leading to H2O2 formation. Overall, these findings demonstrate the substantial impact of ammonia addition on DME ignition, highlighting the need for further research to better understand NH3/DME binary fuel ignition and to optimize the design and operation of NH3/DME dual-fuel engines for improved efficiency and reliability.

Enhanced dye degradation using MIL-53(Fe)-Modified kraft lignin as a heterogeneous Fenton catalyst

MIL-53(Fe), a metal–organic framework (MOF), is capable of degrading harmful organic contaminants, but it has relatively low Fenton catalytic efficiency. To enhance the degradation performance of MIL-53(Fe), we synthesized MIL-53(Fe)-MKL by incorporating modified kraft lignin (MKL) into pristine MIL-53(Fe). The as-prepared composite demonstrated Fenton activity, degrading 97 % of methylene blue (MB) within 50 min. Compared to pristine MIL-53(Fe) (which achieved 62.4 % MB degradation), the MIL-53(Fe)-MKL composite showed a 34.6 % improvement in MB degradation under identical reaction conditions. The incorporated MKL promotes Fe2+ regeneration from Fe3+ in the Fenton process, activating H2O2 to produce OH radicals, which were identified through scavenging experiments and chemical dosimetry with ESR analysis. The MIL-53(Fe)-MKL composite was reused for at least five cycles without a significant decrease in catalytic efficiency. This reported catalyst takes advantage of both MKL and MIL-53(Fe) to enhance catalytic activity, providing a basis for developing innovative catalysts for organic pollutant degradation.

Cytotoxic and radical activities of metal-organic framework modified with iron oxide: Biological and physico-chemical analyses

Metal-organic framework (MOF) modified with iron oxide, Fe3O4-MOF, is a perspective drug delivery agent, enabling magnetic control and production of active hydroxyl radicals, •OH, via the Fenton reaction. This paper studies cytotoxic and radical activities of Fe-containing nanoparticles (NPs): Fe3O4-MOF and its components – bare Fe3O4 and MOF (MIL-88B). Luminous marine bacteria Photobacteriumphosphoreum were used as a model cellular system to monitor bioeffects of the NPs. Neither the NPs of Fe3O4-MOF nor MOF showed cytotoxic effects in a wide range of concentrations (<10 mg/L); while Fe3O4 was toxic at >3·10−3 mg/L. The NPs of Fe3O4 did not affect the bacterial bioluminescence enzymatic system; their toxic effect was attributed to cellular membrane processes. The integral content of reactive oxygen species (ROS) was determined using a chemiluminescence luminol assay. Bacteria mitigated excess of ROS in water suspensions of Fe3O4-MOF and MOF, maintaining bioluminescence intensity closer to the control; this resulted in low toxicity of these NPs. We estimated the activity of •OH radicals in the NPs samples with physical and chemical methods – spin capture technology (using electron paramagnetic resonance spectroscopy) and methylene blue degradation. Physico-chemical interpretation of cellular responses is provided in terms of iron content, iron ions release and •OH radical production.

A Bulk Oxygen Vacancy Dominating WO3-x Photocatalyst for Carbamazepine Degradation.

Creating oxygen vacancy in tungsten trioxide (WO3) has been considered as an effective strategy to improve the photocatalytic performance for degrading organic pollutants. In this study, oxygen vacancies were introduced into WO3 by thermal treatment under Ar atmosphere and their proportion was changed by setting different treatment times. WO3-x samples show better photoelectric properties and photocatalytic degradation performance for carbamazepine (CBZ) than an oxygen-vacancy-free sample, and WO3-x with the optimal proportion of oxygen vacancies is obtained by thermal treatment for 3 h in 550 °C. Furthermore, it discovers that the surface oxygen vacancies on WO3-x would be recovered when it is exposed to air, resulting in a bulk oxygen vacancy dominating WO3-x (bulk-WO3-x). The bulk-WO3-x exhibited much higher degradation efficiency for CBZ than WO3-x with both surface and bulk oxygen vacancies. The mechanism study shows bulk-WO3-x mainly degrades the CBZ by producing OH radicals and superoxide radicals, while oxygen-vacancy-free sample mainly oxidizes the CBZ by the photoexcited hole, which requires the CBZ to be adsorbed on the surface for degradation. The radical generated by bulk-WO3-x exhibits stronger oxidizing capacity by migrating to the solution for CBZ degradation. In summary, the influence of oxygen vacancy on photocatalytic degradation performance depends on both the proportion and location distribution and could lie in the optimization of the photodegradation mechanism. The results of this study could potentially broaden our understanding of the role of oxygen vacancies and provide optimal directions and methods for oxygen vacancy regulation for photocatalysts.

Exploring secondary aerosol formation associated with elemental carbon in the lower free troposphere

The variability of element carbon (EC) mixed with secondary species significantly complicates the assessment of its environmental impact, reflecting the complexity and diversity of EC-containing particles' composition and morphology during their ascent and regional transport. While the catalytic role of EC in secondary aerosol formation is recognized, the effects of heterogeneous chemistry on secondary species formation within diverse EC particle types are not thoroughly understood, particularly in the troposphere. Alpine sites offer a prime environment to explore EC properties post-transport from the ground to the free troposphere. Consequently, we conducted a comprehensive study on the genesis of secondary aerosols in EC-containing particles at Mt. Hua (altitude: 2069 m) from 1 May to 10 July, using a single particle aerosol mass spectrometer (SPAMS). Our analysis identified six major EC particle types, with EC-K, EC-SN, and EC-NaK particles accounting for 27.6 %, 27.0 %, and 19.6 % of the EC particle population, respectively. The concentration-weighted trajectory (CWT) indicated that the lower free troposphere over Mt. Hua is significantly affected by anthropogenic emissions at ground-level, predominantly from northwestern and eastern China. Atmospheric interactions are crucial in generating high sulfate levels in EC-SN and EC-OC particles (> 70 %) and notable nitrate levels in EC-K, EC-BB, and EC-Fe particles (> 80 %). The observed high chloride content in EC-OC particles (56 ± 32 %) might enhance chlorine's reactivity with organic compounds via heterogeneous reactions within the troposphere. Distinct diurnal cycles for sulfate and nitrate are mainly driven by varying transport dynamics and formation processes, showing minimal dependency on EC particle types. Enhanced nocturnal oxalate conversion in EC-Fe particles is likely due to the aqueous oxidation of precursors, with Fe-catalyzed Fenton reactions enhancing OH radical production. This investigation provides critical insights into EC's role in secondary aerosol development during its transport in the lower free troposphere.

The Impact of Agroecosystems on Nitrous Acid (HONO) Emissions during Spring and Autumn in the North China Plain.

Solar radiation triggers atmospheric nitrous acid (HONO) photolysis, producing OH radicals, thereby accelerating photochemical reactions, leading to severe secondary pollution formation. Missing daytime sources were detected in the extensive HONO budget studies carried out in the past. In the rural North China Plain, some studies attributed those to soil emissions and more recent studies to dew evaporation. To investigate the contributions of these two processes to HONO temporal variations and unknown production rates in rural areas, HONO and related field observations obtained at the Gucheng Agricultural and Ecological Meteorological Station during spring and autumn were thoroughly analyzed. Morning peaks in HONO frequently occurred simultaneously with those of ammonia (NH3) and water vapor both during spring and autumn, which were mostly caused by dew and guttation water evaporation. In spring, the unknown HONO production rate revealed pronounced afternoon peaks exceeding those in the morning. In autumn, however, the afternoon peak was barely detectable compared to the morning peak. The unknown afternoon HONO production rates were attributed to soil emissions due to their good relationship to soil temperatures, while NH3 soil emissions were not as distinctive as dew emissions. Overall, the relative daytime contribution of dew emissions was higher during autumn, while soil emissions dominated during spring. Nevertheless, dew emission remained the most dominant contributor to morning time HONO emissions in both seasons, thus being responsible for the initiation of daytime OH radical formation and activation of photochemical reactions, while soil emissions further maintained HONO and associated OH radial formation rates at a high level, especially during spring. Future studies need to thoroughly investigate the influencing factors of dew and soil emissions and establish their relationship to HONO emission rates, form reasonable parameterizations for regional and global models, and improve current underestimations in modeled atmospheric oxidation capacity.

Ignition characteristics of ammonia-methanol blended fuel in a rapid compression machine

Ammonia has attracted wide attention in recent years as a carbon-free fuel. However, the low reactivity and combustion inertness of ammonia pose challenges to its applications in engines. Adding highly reactive fuels, such as renewable carbon–neutral methanol, offers a potential solution. To investigate the ignition characteristics of ammonia-methanol blended fuel, ignition delay time measurement and fast gas sampling under stoichiometric conditions with four ammonia blending ratios (20 % ammonia, A20; 40 % ammonia, A40; 80 % ammonia, A80; 95 % ammonia, A95) were carried out on a rapid compression machine under engine-relevant conditions. The effective thermodynamic conditions were 15–25 bar and 810–970 K. The concentrations of fuels NH3, CH3OH, and intermediate species N2O, CO, as well as products N2, CO2 were detected using gas chromatography. Chemical analysis was performed based on simulations using five ammonia-methanol reaction mechanisms. The ignition delay time results showed that the addition of methanol shortened the ignition delay time, with only a little change in ignition delay time beyond 20 % methanol content. Methanol significantly promoted the production of OH radical, leading to the enhancement of the overall mixture reactivity. The sampling results showed different consumption patterns of ammonia and methanol during the ignition process at different mixing ratios. For A80, methanol was consumed from the early stage of the ignition process, while ammonia consumption was negligible in the early stage. Conversely, for A95, ammonia consumption began in the early stage. This suggests that methanol and its intermediate species inhibited the consumption of ammonia, however, ammonia promoted the consumption of methanol. Chemical analysis further revealed that the inhibitory effect of methanol on ammonia consumption was weakened with the decrease of methanol proportion.

An eco-friendly self-assembled catalyst preparation and study of tetracycline degradation: Performance, mechanism to application

Chloromethyl styrene resin can undergo specific chemical modifications and is an excellent adsorbent material for treating difficult-to-degrade substances in wastewater. In this study, chloromethyl styrene resin will be used as a carrier, and polystyrene chloromethyl resin (PS-Cl) was converted into PS-NH2 by amino modification. The self-assembly of cobalt-based metal–organic framework (CoMOF) was induced on the surface of PS-NH2 by using a novel preparation technique. The performance of the prepared PS-NH2@CoMOF self-assembled catalysts with core–shell-like structures in degrading the target pollutant, tetracycline (TC), was evaluated. The catalysts effectively induced rapid OH radical production from H2O2, had a degradation rate of as high as 88.3 % for 20 mg/L TC solution, and were highly stable and adaptable to aqueous environments. Free radicals and intermediates in the catalytic degradation process were detected by electron paramagnetic resonance and high-performance liquid chromatography mass spectrometry, and possible catalytic degradation pathways were analyzed. The catalytic dissociation behavior of H2O2 in the presence of different catalysts was studied in depth and compared with that of similar metal–organic framework materials through density-functional theory calculations. Results demonstrated the excellent performance of the PS-NH2@CoMOF catalysts. Finally, the catalysts' potential for use in practical engineering applications was evaluated with a flow column experimental model, and the results were more than satisfactory. Therefore, the use of the catalysts to degrade TC has great potential.

Exploring NH3 combustion in environments with CO2 and H2O via reactive molecular dynamics

In existing power units such as internal combustion engines and gas turbines, the combustion of ammonia mixed with hydrocarbon fuels can effectively enhance the combustion intensity of ammonia. In the duel-fuel combustion scenario, the effect mechanism of the main components of combustion exhaust gas i.e., CO2 and H2O on ammonia combustion is still unclear and needs to be studied. Therefore, this paper uses reactive molecular dynamics simulations to study the combustion and emission processes of ammonia in environments with CO2 and H2O. The effects of the diverse gas environments (N2/O2, O2/CO2, and O2/CO2/H2O environments), high CO2 levels, varying H2O proportions, and O2 concentrations on ammonia combustion and emission were systematically explored. It was found that ammonia consumption was accelerated in the O2/CO2/H2O environments compared to N2/O2 environments, resulting in more NH2, H2, and H2O production. The effect of high CO2 concentration on ammonia oxidation was mainly related to temperature. The simulations found that the high CO2 concentration inhibited ammonia consumption at T < 2800K while enhancing it at T ⩾ 2800K. In addition, the high CO2 concentration could inhibit NO production under stoichiometric conditions but promote the conversion of nitrogen-containing intermediates to NO with the oxidizing capacity of CO2 enhanced significantly under extremely high temperature conditions. It was found that the increasing content of H2O molecules in the environment promoted NO production and inhibited CO production under stoichiometric conditions. In addition, the reaction paths for the conversion of HNO and HNO2 molecules into NO molecules were significantly enhanced with increasing H2O concentration. The increase in oxygen concentration can promote OH radical production and NO formation at high temperatures.

A shock tube study of the ignition delay time of DME/ammonia mixtures: Effect of fuel blending from high temperatures to the NTC regime

An experimental and chemical kinetic investigation has been conducted to understand the effect of dimethyl ether (DME) blending on the ignition delay time of ammonia (NH3) from high temperatures to the negative temperature coefficient (NTC) regime in a shock tube with the DME fractions of 0 %, 5 %, 25 %, 50 %, and 100 %, temperatures of 690–1810 K, pressures of 1.2 and 10 atm, and equivalence ratio of 1.0. Four representative literature chemical kinetic models were validated against our measurements, however none of the above models can provide reasonable predictions of the experimental data in the NTC regime. A chemical kinetic model was developed in this study, the model was also been validated by the ignition delay times, laminar flame speeds and specie profiles data of DME/ammonia mixtures in the literature. Experimental results show that the ignition delay times of NH3 can be obviously shorten by 5 % DME addition in both high temperature and the NTC region. Chemical kinetic analyses reveal that the addition of 5 % DME can rapidly generate OH radical through the reaction pathway of HO2 → H2O2 → OH at 1250 K. At 800 K, the blended DME can be rapidly consumed via the reaction pathway of R → RO2 → QOOH → OOQOOH to promote the production of OH radical in the early stage, thus lead to the reduced ignition delay time of DME/NH3 mixture.

Dumbbell-shaped bimetallic AuPd nanoenzymes for NIR-II cascade catalysis-photothermal synergistic therapy

The noble metal NPs that are currently applied to photothermal therapy (PTT) have their photoexcitation location mainly in the NIR-I range, and the low tissue penetration limits their therapeutic effect. The complexity of the tumor microenvironment (TME) makes it difficult to inhibit tumor growth completely with a single therapy. Although TME has a high level of H2O2, the intratumor H2O2 content is still insufficient to catalyze the generation of sufficient hydroxide radicals (‧OH) to achieve satisfactory therapeutic effects. The AuPd-GOx-HA (APGH) was obtained from AuPd bimetallic nanodumbbells modified by glucose oxidase (GOx) and hyaluronic acid (HA) for photothermal enhancement of tumor starvation and cascade catalytic therapy in the NIR-II region. The CAT-like activity of AuPd alleviates tumor hypoxia by catalyzing the decomposition of H2O2 into O2. The GOx-mediated intratumoral glucose oxidation on the one hand can block the supply of energy and nutrients essential for tumor growth, leading to tumor starvation. On the other hand, the generated H2O2 can continuously supply local O2, which also exacerbates glucose depletion. The peroxidase-like activity of bimetallic AuPd can catalyze the production of toxic ‧OH radicals from H2O2, enabling cascade catalytic therapy. In addition, the high photothermal conversion efficiency (η = 50.7 %) of APGH nanosystems offers the possibility of photothermal imaging-guided photothermal therapy. The results of cell and animal experiments verified that APGH has good biosafety, tumor targeting, and anticancer effects, and is a precious metal nanotherapeutic system integrating glucose starvation therapy, nano enzyme cascade catalytic therapy, and PTT therapy. This study provides a strategy for photothermal-cascade catalytic synergistic therapy combining both exogenous and endogenous processes. Statement of SignificanceAuPd-GOx-HA cascade nanoenzymes were prepared as a potent cascade catalytic therapeutic agent, which enhanced glucose depletion, exacerbated tumor starvation and promoted cancer cell apoptosis by increasing ROS production through APGH-like POD activity. The designed system has promising photothermal conversion ability in the NIR-II region, simultaneously realizing photothermal-enhanced catalysis, PTT, and catalysis/PTT synergistic therapy both in vitro and in vivo. The present work provides an approach for designing and developing catalytic-photothermal therapies based on bimetallic nanoenzymatic cascades.

Effective removal of As from a high arsenic-bearing ZnSO4 solution by ultrasonic enhanced ozonation in a one-pot method

Currently, removing arsenic (As) from ZnSO4 solution using lime presents several drawbacks, including high wet precipitate content, long reaction time, and the introduction of new impurities. In this study, we propose a novel ultrasonic (US) ozone one-pot method for effectively removing As from a high-arsenic ZnSO4 solution. In this method, as in ZnSO4 solution was removed by ultrasound enhanced ozone oxidation combined with zinc roasting dust (ZRD). No secondary pollution will occur with the addition of ZRD and ozone, as neither introduces new impurities. The experimental results show that under the conditions of initial As and Fe concentrations of 1640 mg/L and 2963 mg/L, US power of 480 W, frequency of 20 kHz, reaction temperature of 60 °C, reaction time of 1 h, ZRD dose of 12 g/L and gas flow rate of 900 mL/min, the removal rate of As can reach 99.4%. The introduction of US can further enhance the oxidation effect of ozone on As(III) and Fe2+ by increasing the solubility of ozone and promoting the production of OH radicals. Additionally, US cavitation and mechanical action increase the probability of contact between various reactants in the solution, facilitating the occurrence of reactions. US also reduces the aggregation of arsenic-containing precipitates and the encapsulation of ZRD by arsenic containing precipitates, thereby decreasing the amount of arsenic-containing precipitates. In comparison to the traditional lime method, this approach results in a significant reduction in the amount of arsenic-containing precipitate by 54.5% and a 60% decrease in the total reaction time. The As removal mechanism of our method encompasses ZRD neutralization, US-enhanced ozone mass transfer and decomposition, oxidation of As(III) and Fe2+, and adsorption and coprecipitation. Consequently, the proposed method provides a cost-effective, fast, safe and environmentally friendly alternative for treating arsenic-contaminated ZnSO4 solutions.

Photochemical ageing of aerosols contributes significantly to the production of atmospheric formic acid

Abstract. Formic acid (HCOOH) is one of the most abundant organic acids in the atmosphere and affects atmospheric acidity and aqueous chemistry. However, the HCOOH sources are not well understood. In a recent field study, we measured atmospheric HCOOH concentrations at a coastal site in southern China. The average concentrations of HCOOH were 191 ± 167 ppt in marine air masses and 996 ± 433 ppt in coastal air masses. A strong linear correlation between HCOOH concentrations and the surface area densities of submicron particulate matter was observed in coastal air masses. Post-campaign laboratory experiments confirmed that the photochemical ageing of ambient aerosols promoted by heterogeneous reactions with ozone produced a high concentration of HCOOH at a rate of 0.185 ppb h−1 under typical ambient conditions at noon. HCOOH production was strongly affected by nitrate photolysis, as this efficiently produces OH radicals that oxidise organics to form HCOOH. We incorporated this particle-phase source into a photochemical model, and the net HCOOH production rate increased by about 3 times compared with the default Master Chemical Mechanism (MCM). These findings demonstrate that the photochemical ageing of aerosols is an important source of HCOOH that should be included in atmospheric chemistry–transport models.

The generation pathways of OH and H2O2 by plasma-liquid interactions

Plasma-liquid interactions (PLIs) are a rich source providing many reactive oxygen species (ROS). These ROS species, such as OH and H2O2, feature powerful oxidative properties, which are excellent utilization for bacterial killing, water treatment, and other applications. Lifetime and reaction pathways of ROS species from plasma into the bulk liquid are complex. Understanding these behaviors is essential for the applications of the ROS species. In this work, we presented two pathways for generation of OH radicals and H2O2 from the plasma into the bulk liquid. Firstly, OH radicals are mainly produced via the dissociation of water molecules by free electrons in the plasma. Generated radicals then quickly recombine into H2O2. These species with a high Henry constant easily absorb and disperse into the bulk liquid. In a second way, OH radicals and H2O2 are also generated by the reaction of O3 with H2O molecules. At first, O3 is absorbed into the bulk liquid and reacts with H2O2 molecules to generate H2O2. Next, O3 continues reacting with this generated H2O2 to produce OH radicals.

Effects of hydrogen peroxide on the low-temperature ignition delay times of ethylene/air/Ar mixtures in an RCM

Hydrogen peroxide with strong oxidative activity has received increasing attention in the field of ignition and combustion enhancement. To further seek out its potential benefits in ignition, the effects of hydrogen peroxide on the ignition delay times of ethylene were experimentally investigated using a rapid compression machine and numerically analyzed via the AramcoMech 3.0. The experiments with different levels of hydrogen peroxide (0 – 7000 ppm) were performed at Pc = 3.33 MPa, Tc = 817.9 – 921.0 K, φ = 0.5 – 1.5, and a dilution of 45 mol% Ar. Experimental results showed that adding hydrogen peroxide can effectively shorten the ignition delay times, and extend the low-temperature limitations. The improving effect was proceeded by three stages (0 – 1000 ppm, 1000 – 4000 ppm, and 4000 – 7000 ppm) of different decreasing rates. Kinetic analyses revealed that adding hydrogen peroxide promoted the production of OH radical to highlight the H-abstraction reaction of ethylene, further accelerating the oxidation of vinyl to vinyloxy and then to formaldehyde. Moreover, higher heat release rates were obtained with the addition of hydrogen peroxide for its exothermic character. By the kinetic effects of hydrogen peroxide addition, the ignition delay times of ethylene/air/Ar mixtures were significantly decreased. However, with the increase of additive fraction, the growth rate of both heat release rate and rate of production of OH radical were slowed down, lessening the enhancement effect on the ignition delay times.

Ozonolysis of ketoprofen in polluted water: Reaction pathways, kinetics, removal efficiency, and health effects

Ketoprofen (KET), as a non-steroidal anti-inflammatory drug frequently detected in aqueous environments, is a threat to human health due to its accumulation and low biodegradability, which requires the transformation and degradation of KET in aqueous environments. In this paper, the reaction process of ozone-initiated KET degradation in water was investigated using density functional theory (DFT) method at the M06-2X/6-311++g(3df,2p)//M06-2X/6-31+g(d,p) level. The detailed reaction path of KET ozonation is proposed. The thermodynamic results show that ozone-initiated KET degradation is feasible. Under ultraviolet irradiation, the reaction of ozone with water can also produce OH radicals (HO·) that can react with KET. The degradation reaction of KET caused by HO· was further studied. The kinetic calculation illustrates that the reaction rate (1.99 × 10−1 (mol/L)−1 sec−1) of KET ozonation is relatively slow, but the reaction rate of HO· reaction is relatively high, which can further improve the degradation efficiency. On this basis, the effects of pollutant concentration, ozone concentration, natural organic matter, and pH value on degradation efficiency under UV/O3 process were analyzed. The ozonolysis reaction of KET is not sensitive to pH and is basically unaffected. Finally, the toxicity prediction of oxidation compounds produced by degradation reaction indicates that most of the degradation products are harmless, and a few products containing benzene rings are still toxic and have to be concerned. This study serves as a theoretical basis for analyzing the migration and transformation process of anti-inflammatory compounds in the water environment.

Experimental setup for probing electron-induced chemistry in liquid micro-jets

We present an experimental setup for probing chemical changes in liquids induced by electron collisions. The setup utilizes a custom-designed electron gun that irradiates a liquid microjet with an electron beam of tunable energy. Products of the electron-induced reactions are analyzed ex-situ. The microjet system enables re-circulation of the liquid and thus multiple irradiation of the same sample. As a proof-of-principle experiment, an aqueous solution of TRIS (2-Amino-2-(hydroxymethyl)propane-1,3-diol) was irradiated by 300 eV electron beam. Optical UV–VIS analysis shows that the electron impact on the liquid surface leads to the production of OH radicals in the solution which are efficiently scavenged by TRIS.