OH Radicals Research Articles

Photochemistry of Microsolvated Nitrous Acid: Observation of the Water-Separated Complex of Nitric Oxide and Hydroxyl Radical.

The photochemistry of nitrous acid (HONO) plays a crucial role in atmospheric chemistry as it serves as a key source of hydroxyl radicals (OH) in the atmosphere; however, our comprehension of the underlying mechanism for the photochemistry of HONO especially in the presence of water is far from being complete as the transient intermediates in the photoreactions have not been observed. Herein, we report the photochemistry of microsolvated HONO by water in a cryogenic N2 matrix. Specifically, the 1:1 hydrogen-bonded water complex of HONO was facially prepared in the matrix through stepwise photolytic O2 oxidation of the water complex of imidogen (NH-H2O) via the intermediacy of the elusive water complex of peroxyl isomer HNOO. Upon photolysis at 193 nm, the matrix-isolated HONO-H2O complex decomposes by yielding the ternary water complex of OH and NO due to the matrix cage effect. The identification of this rare water-separated radical pair (OH-H2O-NO) with matrix-isolation infrared and ultraviolet-visible spectroscopy is aided by D, 15N, and 18O isotope labeling and quantum chemical calculations at the (U)CCSD/AVTZ level of theory, and its most stable structure exhibits separate hydrogen bonding interactions of the OH and NO radicals with H2O via OH···OH2 and ON···HOH contacts, respectively. This ternary complex is extremely unstable, as it undergoes spontaneous radical recombination to reform the HONO-H2O complex in the temperature range of 4-12 K through quantum-mechanical tunneling with 16/18O, H/D, 14/15N kinetic isotopic effects of 1.43, 2.33, and 0.91, respectively. At increased temperatures from 15 to 21 K, the recombination proceeds predominantly by overcoming the activation barrier with an estimated height of 0.12(1) kcal/mol.

Kinetic Laser Absorption Spectroscopy of Vibrationally Excited Hydroxyl Radicals on Infrared Transitions ν = 3 ← 1 and ν = 4 ← 2

The kinetics of vibrationally excited OH(ν = 1) and OH(ν = 2) radicals was studied by time-resolved laser absorption in the overtone IR region. Two DFB laser diodes, 1509.3 and 1589 nm, were used. The technique allowed for the reliable study of the vibrational relaxation kinetics as well as the relative populations of the vibrationally excited states. The yields of OH(ν = 1) and OH(ν = 2) in the reaction O(1D) + H2O were determined. The rate constant of OH(ν = 1) relaxation in collision with water molecules was obtained ((9.2 ± 2.0) × 10−12 cm3/s). The dynamics of OH(ν = 1) and OH(ν = 2) populations were analyzed in detail, which made it possible to separately determine the relative contribution of the vibrational ladder relaxation channels OH(ν = 2) → OH(ν = 1) → OH(ν = 0) and the direct relaxation OH(ν = 2) → OH(ν = 0).

Fabricating Lattice-Confined Pt Single Atoms With High Electron-Deficient State for Alkali Hydrogen Evolution Under Industrial-Current Density.

The confining effect is essential to regulate the activity and stability of single-atom catalysts (SACs), but the universal fabrication of confined SACs is still a great challenge. Here, various lattice-confined Pt SACs supported by different carriers are constructed by a universal co-reduction approach. Notably, Pt single atoms confined in the lattice of Ni(OH)2 (Pt1/Ni(OH)2) with a high electron-deficient state exhibit excellent activity for basic hydrogen evolution reaction (HER). Specifically, Pt1/Ni(OH)2 just requires 15mV to get 10mA cm-2 and the mass activity of Pt1/Ni(OH)2 is 15 times of commercial Pt/C. Moreover, Pt1/Ni(OH)2 assembled in an alkaline water electrolyzer shows 1030h durability under the industrial current density of 800mA cm-2. In situ spectroscopy techniques reveal Pt─H and "free" OH radical can be directly observed for Pt1/Ni(OH)2, confirming the lattice-confined Pt single atoms play a key role during HER. Further density functional theory uncovers the Pt 3d orbital strongly hybridizes with O 2p and Ni 3d orbitals in Ni(OH)2, which quickly optimizes the electronic state of the Pt site, thus largely reducing the energy barrier of the rate-determining step to 0.16eV for HER. Finally, this synthesis method is extended to construct other 9 lattice-confined SACs.

Mechanism of Curcuma phaeocaulis Extracts on the Proliferation and Apoptosis of Gallbladder Cancer Cells via mTOR/p70S6K Signaling Pathway

Background Curcuma phaeocaulis (CP) is utilized as a Chinese herbal medicine to treat abdominal distension and other related ailments. Curcuma phaeocaulis extracts (CPE) are rich in active components and exhibit anti-tumor properties. Purpose Purpose: This work was to assess the impact of CPE on the proliferation, apoptosis, migration, and invasion of gallbladder cancer cells (GCC), aiming to investigate its potential underlying mechanisms of action. Methods CP was utilized as the raw material to prepare CPE volatile oil via drying and heating processes. Total phenolic content analysis was conducted, assessing its scavenging capacity against 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and •OH free radicals, as well as its inhibitory effects on the growth of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Human GCC line GBC-SD was selected, cultured conventionally as a control, and treated with CP volatile oil at concentrations of 25 µg/mL (Low-CPE group), 50 µg/mL (Middle-CPE group), and 100 µg/mL (High-CPE group). Cell proliferation activity was evaluated using MTT assay, apoptosis rate was assessed via flow cytometry, migration, and invasion were measured using the Transwell chamber assay, and Western blot was performed to assess proteins in the mTOR/p70S6K signaling pathway. Results The total phenolic content in the volatile oil prepared from warm CPE was approximately 30.9 mg/g, consisting of over 20 active constituents. The warm CP volatile oil exhibited scavenging rates of 85.3% for DPPH• radicals and 91.5% for •OH radicals, with minimum inhibitory concentrations against S. aureus, E. coli, and P. aeruginosa at 4.0 mg/mL, 8.0 mg/mL, and 1.0 mg/mL, respectively. Relative to the Ctrl group, Low-CPE, Middle-CPE, and High-CPE groups demonstrated decreased cell proliferation activity, increased apoptosis rates, reduced cell migration and invasion, decreased phosphorylation levels of mTOR and p70S6K proteins ( p < 0.05), exhibiting concentration-dependent characteristics. Conclusion The volatile oil derived from warm CPE exhibited robust anti-oxidant and anti-bacterial activities. The warm CP volatile oil effectively inhibited GCC proliferation, migration, and invasion by suppressing the activation of the mTOR/p70S6K signaling, while promoting apoptosis.

The Atmospheric Chemistry of Fluoroacetonitrile and the Characterization of the Major Product, Cyanoformyl Fluoride

Fluorinated nitriles have been proposed as low-global-warming-potential substitutes for industrial applications such as plasma etching and as dielectric materials in high-voltage equipment. FT-IR spectroscopy was used to measure the radiative efficiency of CH2FCN and its reactivity towards Cl and OH radicals, and to determine products from the Cl reaction. Relative rate experiments yielded rate constants for Cl and OH reactions of (2.1 ± 0.3) × 10−14 and (7.0 ± 1.0) × 10−14 cm3 molecule−1 s−1, respectively. The estimated atmospheric lifetime of CH2FCN with respect to radical attack was estimated to be 0.45 years, which, combined with the radiative efficiency of 0.042 W m−2 ppb−1, implies a 100-year global warming potential of 20. FCOCN was observed as the only organic product of the Cl-atom reaction in air, consistent with a dominant role for H-abstraction. Absolute infrared cross-sections for FCOCN were determined, to assist future experiments where this molecule may be formed. Quantum calculations at the CBS-APNO//B2PLYP-D3/cc-pVTZ level indicate similar energy barriers to addition and abstraction for OH radical attack, but the looser transition state and greater opportunity for tunneling also favor abstraction in this case.

Converting Fe-N-C single-atom catalyst to a new FeNxSey cluster catalyst for proton-exchange membrane fuel cells.

Fe-N-C catalyst is the most promising alternative to platinum catalyst for proton-exchange membrane fuel cells (PEMFCs), however its high performance cannot be maintained for a long enough time in device. The construction of a new Fe coordination environment that is different from the square-planar Fe-N 4configuration in Fe-N-C catalyst is expected to break current stability limits, which however remains unexplored. Here, we report the conversion of Fe-N-C to a new FeNxSey catalyst, where the Fe sites are three-dimensionally (3D) co-coordinated by N and Se atoms. The FeNxSeycatalyst exhibits much better 4e-ORR activity and selectivity than the Fe-N-C catalyst. Specifically, the yields of H2O2 and ·OH radicals on FeNxSeyare only one-quarter and one-third of that on Fe-N-C, respectively. Therefore, the FeNxSeycatalyst exhibits outstanding stability, losing only 10 mV in E1/2after 10,000 cycles, much smaller than that of the Fe-N-C catalyst (56 mV), representing the most stable Pt-free catalysts ever reported. Moreover, the 3D co-coordination structureinhibits the Fe demetallization in the presence of H2O2. As a result, the FeNxSeybased PEMFC shows excellent durability, with the current density attenuation significantly lower than that of the Fe-N-C based device after accelerated durability testing.

Absolute line strength measurements of HO2 radical in the OO-stretching fundamental band between 1088 and 1124cm-1 using time-resolved dual-comb spectroscopy.

Absolute line strength measurements of hydroperoxyl (HO2) radical in the OO-stretching (ν3) fundamental band have been performed by means of mid-infrared time-resolved dual-comb spectroscopy. By employing two sets of dual-comb spectrometers, high-resolution time-resolved spectra of HO2 and HCl, formed in the photolysis reaction system of Cl2/CH3OH/O2, could be, respectively, measured near 1123 and 3059cm-1. With kinetic simulations, spectral analysis of both HO2 and HCl, as well as the accurate line strength of the HCl R(9) transition at 3059.316cm-1, an absolute line strength of the ν3 131,13 ← 121,12 F1,2 transitions in HO2 at 1122.983cm-1 was first determined to be 1.80 × 10-20cmmolecule-1 with a small uncertainty down to 4% under the conditions with low initial concentrations of Cl radical (1.63-1.81 × 1013moleculecm-3). Furthermore, broadband high-resolution spectra of the ν3 fundamental band of HO2 were recorded in the range of 1088-1124cm-1 with an average spectral resolution of 0.002cm-1. By contour fitting the measured broadband spectra with PGOPHER, the line strengths of hundreds of rovibrational transitions were obtained relative to the well-determined HO2 lines at 1122.983cm-1, and those values were observed to be higher than those tabulated in the HITRAN database by a factor of ∼2.8. Moreover, the absolute band strength of the ν3 fundamental band in HO2 was derived to be 22.3 km mol-1 with an uncertainty of 5%. This work providing precise and detailed spectral data would be crucial in revisiting the theoretical modeling of HO2 geometry and updating the database of the HO2 radical.

Methane oxidation to ethanol by a molecular junction photocatalyst.

Methane, the major component of natural and shale gas, is a significant carbon source for chemical synthesis. The direct partial oxidation of methane to liquid oxygenates under mild conditions1-3 is an attractive pathway, but the molecule's inertness makes it challenging to achieve simultaneously high conversion and high selectivity towards a single target product. This difficulty is amplified when aiming for more valuable products that require C-C coupling4,5. While selective partial methane oxidation processes1-3,6-9 have thus typically generated C1 oxygenates6,7, recent reports have documented photocatalytic methane conversion to the C2 oxygenate ethanol with low conversions but good to high selectivities4,5,8-12. Here, we show that the intramolecular junction photocatalyst CTF-1 with alternating benzene and triazine motifs7,13 drives methane coupling and oxidation to ethanol with a high selectivity and much improved conversion. The heterojunction architecture not only enables efficient and long-lived separation of charges after their generation, but also preferential adsorption of H2O and O2 to the triazine and benzene units, respectively. This dual-site feature separates C-C coupling to form ethane intermediates from the sites where •OH radicals are formed and thereby avoids overoxidation. When loaded with Pt to boost performance further, the molecular heterojunction photocatalyst generates ethanol in a packed-bed flow reactor with improved conversion that results in an apparent quantum efficiency of 9.4%. We anticipate that further developing the "intramolecular junction" approach will deliver efficient and selective catalysts for C-C coupling, pertaining, but not limited, to methane conversion to C2+ chemicals.

Rapid Iron-Mediated Aqueous-Phase Reactions of Organic Peroxides from Monoterpene-Derived Criegee Intermediates and Implications for Aerosol and Cloud Chemistry.

Fenton-like reactions between organic peroxides and transition-metal ions in the atmospheric aqueous phase have profound impacts on the chemistry, composition, and health effects of aerosols. However, the kinetics, mechanisms, and key influencing factors of such reactions remain poorly understood. In this study, we synthesized a series of monoterpene-derived α-acyloxyalkyl hydroperoxides (AAHPs), an important class of organic peroxides formed from Criegee intermediates during the ozonolysis of alkenes, and investigated their Fenton-like reactions with iron ions in the aqueous phase. We found that the AAHPs are essentially chemically inert to Fe3+ but highly reactive toward Fe2+. The aqueous-phase reaction rate constant between AAHPs and Fe2+ (kIIAAHP+Fe(II)) was determined to range between 11.0 ± 0.8 and 150.0 ± 3.3 M-1 s-1, depending positively on the solution pH (1-3), water content (50%-90%), and temperature (8-25 °C). Meanwhile, the kIIAAHP+Fe(II) value is linearly correlated to the O/C ratio of AAHPs, which allows for the estimation of the Fenton-like reactivity of AAHPs based on their oxygenation level. In addition, the decomposition of AAHPs via Fenton-like reactions with Fe2+ predominantly yields alkoxy (RO) radicals with the production yield of OH radicals smaller than 16%. Similar to synthesized AAHPs, several abundant peroxides including the pinonic acid-derived AAHP exhibit high Fenton-like reactivity toward Fe2+ but low reactivity toward Fe3+ in dissolved α-pinene secondary organic aerosol. A quantitative analysis based on the measured kinetics suggests that Fenton-like reactions are important and even dominant drivers behind the transformation of AAHPs in the atmosphere, which would significantly affect atmospheric multiphase chemistry and aerosol health impacts.

Production of abiotic or biogenic hydrocarbons on rock particles in the presence of H2O and carbon compounds

Abiotic H2 and hydrocarbons are found in fluids discharged from ultramafic-hosted hydrothermal vents. Beneath the hydrothermal vents, abiotic H2 and hydrocarbons can be formed by serpentinization reactions and Fischer–Tropsch-type hydrocarbon-forming reactions, respectively, over ultramafic rocks. However, the source rocks that form abiotic H2 and hydrocarbons may extend to broader subsurface rocks. Here, we show that various rock constituents (solid acids) play a catalytic role in the formation of H and OH radicals via H2O dissociation, as well as in the formation of diverse hydrocarbons via the synthesis reactions of H radicals and inorganic carbons or by H radical-induced dissociation of organic carbons. The mechanisms and characteristics of these formation processes were explored through a series of reactor-based laboratory experiments. Four types of solid acid-containing rocks were mixed with H2O and a carbon source and reacted at different temperatures and pressures for different reaction periods. The product gases were analyzed via GC/MS. Twenty-nine hydrocarbons up to C11, predominantly including CH4 and aromatic hydrocarbons, were identified when CO2 (inorganic carbon source) and basalt particles were used; in contrast, 42 hydrocarbons up to C11, predominantly including CH4 and aliphatic hydrocarbons, were identified when soybean oil (organic carbon source) and basalt particles were used. The results of this study imply that abiotic H2 and diverse hydrocarbons are produced in the subsurface of Earth regardless of the presence of living organisms and suggest that solid acid-containing rocks near hot springs or volcanic areas can promote CO2 conversion into CH4 with the aid of H radicals supplied from H2O dissociation over the rocks.

Enhancement of Maize (Zea mays var: GS-2) Plant Growth and Yield: Seed Treatment with Non-thermal Plasma using Different Gases

Impact of pre-sowing treatment of maize (Zea mays Var: GS-2) seeds with non-thermal glow discharge plasma on the growth and yield of field grown plants has been investigated. Maize seeds were treated with non-thermal glow discharge plasma produced from five different gases Nitrogen (N2), Helium (He), Argon (Ar), Hydrogen (H2) and Oxygen (O2) before sowing the seeds in the field. Seeds were exposed to 30 W for 240 seconds to glow discharge plasma produced in a cylindrical stainless steel vacuum chamber utilizing an automatic matching network and a 13.56 MHz with the capacity up to 600W RF power source are used. Plasma treated seeds were grown in the field and growth measurements were made at 30, 60 and 90 days after sowing. Pre- sowing treatment with glow discharge plasma enhanced plant height, leaf length and plant fresh weight at all the stages of growth. O2 and N2 plasma treated seeds were more effective than He, H2 and Ar in enhancing the growth and biomass of the plants. The yield parameters are cob length 21% in O2 and 19% in N2, cob weight 36% in O2 and 34% in N2, and 100 seeds weight 39% in O2 and 36% in N2 plasma were significantly enhanced. It is concluded that O2 and N2 plasma Pre-sowing treatment can significantly enhance the biomass and yield of maize plants with O2 slightly higher. Analyzing the characterization with scanning electron microscopy (SEM), and optical emission spectroscopy (OES) of maize seeds. SEM revealed considerable alterations for O2, N2, Ar, and He but no change for H2 plasma treatment. The findings demonstrate that the surface of the starch caryopsis has been altered, exposing an oxygen and nitrogen plasma that has resulted in huge channels and water holes. The OES identified the presence of OH, NO, O, and N2 radicals generated during oxygen and nitrogen plasma treatment, which is contributing to the best result.

Anion Bridged One‐Dimensional Copper‐Based Metal Organic Frameworks as Peroxidase Mimics for Glucose Detection in Apple Fruits

ABSTRACTEnzyme mimics attract wide attentions as detection sensors. However, the widespread application is limited by low efficiency and high cost. Herein, two novel enzyme mimics 1 and 2 were developed with peroxidase‐like activities. The chain‐like structure of 1 exhibited better stability, energy transformation efficiency, and catalytic property than 2. Both of them could generate •OH radicals to oxide chromogenic agents, realizing the colorimetric detection of H2O2. Additionally, under the synergy of glucose oxidase, a cascade strategy for detection of glucose was constructed. This method exhibited excellent selectivity, anti‐interference, and storage performance, as well as a wide linear range (1–60 μM) at pH = 7.4, with the low detection limits of 0.095 and 0.061 μM for 1 and 2, respectively. Furthermore, the strategy was applied for detecting glucose in apple fruit samples. This work overcomes the shortcomings of current enzyme mimics and paves the way for bioanalysis and agricultural applications.

Unraveling the Meaning of Effective Uptake Coefficients in Multiphase and Aerosol Chemistry.

ConspectusReactions of gas phase molecules with surfaces play key roles in atmospheric and environmental chemistry. Reactive uptake coefficients (γ), the fraction of gas-surface collisions that yield a reaction, are used to quantify the kinetics in these heterogeneous and multiphase systems. Unlike rate coefficients for homogeneous gas- or liquid-phase reactions, uptake coefficients are system- and observation-dependent quantities that depend upon a multitude of underlying elementary steps. As such, uptake coefficients adopt complex scaling behavior with reactant concentrations and other physicochemical properties of the interface, making predictions of γ particularly challenging.Typically, γgas is obtained by measuring the loss rate of a gas-phase molecule above a liquid or solid surface, relative to its collision frequency. By definition, γgas ≤ 1. Highly efficient reactions proceed at or near the gas-surface collision frequency and exhibit values of γgas near unity. Alternatively, heterogeneous kinetics are often measured using the consumption rate of a condensed phase reactant normalized to the gas-surface collision frequency, yielding instead an effective uptake coefficient (γeff). In many cases, γeff and γgas are not equal, yielding additional insights into the nature of the reaction. For example, substantial diffusive limitations in the condensed phase may inhibit reactivity, yielding γeff ≪ γgas. In contrast, γeff > γgas in the presence of condensed phase secondary reactions, with values of γeff often exceeding 1 for the case of radical chain reactions.In this Account, we will discuss how measurements of γeff in aerosol can uniquely reveal the origins of complex physical and chemical behavior in multiphase reactions under laboratory conditions. For example, measurements of the scaling of γeff with shell thickness during the ozonolysis of core-shell aerosol yields insight into the relative transport and reaction time scales of gaseous oxidants, while measurements of γeff, as a function of relative humidity (RH) during OH radical oxidation of hygroscopic citric acid aerosol, highlight the role that mixing times of particle-phase reactants play in determining aerosol reaction kinetics. Additionally, the scaling of γeff with oxidant and trace gas concentrations during the oxidation of long-chain hydrocarbons in aerosols by OH radicals and chlorine atoms provides distinctive signatures of the underlying competition between free radical propagation and termination mechanisms. Finally, it is shown how changes in γeff that are induced by careful selection of the molecular structure of the particle-phase reactant help to identify new reaction pathways, such as alternative mechanisms for lipid peroxidation, and to report on the reaction kinetics of short-lived reactive species, including Criegee Intermediates. Together, these examples will demonstrate how proper experimental design and accurate measurements of an effective uptake coefficient can be used to interrogate the fundamental steps governing complex multiphase reaction mechanisms.

The Genetic Expression Difference of A2058 Cells Treated by Plasma Direct Exposure and Plasma-Treated Medium and the Appropriate Treatment Strategy.

Background/Objectives: Cold atmospheric plasma (CAP) has been demonstrated as an adjustable device to generate various combinations of short-lived reactive oxygen and nitrogen species (RONS) and as a promising appliance for cancer therapy. This study investigated the effects of direct and indirect treatments of Argon-based CAP to cancer cells (A2058, A549, U2OS and BCC) and fibroblasts (NIH3T3 and L929) on cell viability. We also aimed to understand whether plasma-generated RONS were involved in this process using genetic evidence. Methods: The intensity of reactive species in the plasma gas and the concentrations of RONS in phosphate-buffered saline (PBS) and cell culture medium were measured. A viability assay was performed after the cells were treated by plasma in PBS and medium with various volumes to realize the lethal effects of plasma under different conditions. Diverse cells were treated in the same solution to compare the sensitivities of different cells to plasma treatments. The gene expression profiles of A2058 cells after the direct and indirect treatments were analyzed by next generation gene sequencing. Accordingly, we discovered the advantages of sequential treatments on cancer therapy. Results: The cumulative concentration of hydroxyterephthalic acid (HTA) revealed that the pre-existing OH radical (•OH) in PBS increased with the treatment durations. However, there was no significant increase in the concentration of HTA in culture medium. HTA was detected in the treatment interface of PBS but not medium, showing the penetration of •OH through PBS. The concentrations of H2O2 and NO2- increased with the treatment durations, but that of NO3- was low. The direct treatments caused stronger lethal effects on cancer cells under certain conditions. The fibroblasts showed higher tolerance to plasma treatments. From gene expression analysis, the initial observations showed that both treatments influenced transcription-related pathways and exhibited shared or unique cellular stress responses. The pre-treatments, especially of direct exposure, revealed better cancer inhibition. Conclusions: The anti-cancer efficiency of plasma could be enhanced by pre-treatments and by adjusting the liquid interfaces to avoid the rapid consumption of short-lived RONS in the medium. To achieve better therapeutic effects and selectivity, more evidence is necessary to find optional plasma treatments.

Exploring Mechanism and Kinetics of 1,4-Dioxane Oxidative Degradation by OH Radical: A Computational Quantum Chemistry Investigation.

This study aims to shed light on the mechanism and kinetics of 1,4-dioxane degradation by hydroxyl radical (OH) across various solvation conditions to evaluate electronic and structural properties at the MP2/aug-cc-pVTZ level. Transition states (TS) structures determined in the gas phase and SMD solvation model reveal similar hydrogen abstraction patterns. In contrast, the explicit solvation model (ES) introduces significant changes, suggesting a kinetic preference for axial pathways. The reaction rate constants, employing Deformed Transition State Theory (d-TST), are consistently higher for axial abstraction. The preference for axial hydrogen abstraction, solvation effects on transition states, and temperature-dependent rate constants are highlighted. Furthermore, the identification of carbon-carbon orbital distortion suggests potential bond breakage. This research provides valuable insights into the reaction between 1,4-dioxane and OH radical across different solvation models and enhances the understanding of the advanced oxidative process.

Direct Photocatalytic Oxidation of Methane to Formic Acid with High Selectivity via a Concerted Proton-Electron Transfer Process.

Light-driven direct conversion of methane to formic acid is a promising approach to convert methane to value-added chemicals and promote sustainability. However, this process remains challenging due to the complex requirements for multiple protons and electrons. Herein, we report the design of WO3-based photocatalysts modified with Pt active sites to address this challenge. We demonstrate that modulating the dimensional effect of Pt on the WO3 support is key to enhancing the catalytic performance of selective CH4-to-HCOOH conversion. The Pt nanoparticles on WO3 exhibit superior conversion rate, selectivity and durability in the production of HCOOH compared to the Pt-free sample and WO3 decorated with Pt single atoms. The optimal PtNPs-WO3 catalyst achieves a HCOOH conversion rate of 17.7 mmol g-1, with 84% selectivity and stability maintained for up to 48 h. Mechanistic studies show that the protonation of O2 to hydroxyl radicals is the limiting step for HCOOH yield. Pt nanoparticles can facilitate electron transfer and promote O2 dissociation, generating hydroxyl radicals via a proton-coupled electron transfer process. This process provides sufficient protons to lower the formation barrier for •OH radicals, thereby promoting the activation of CH4. In addition, Pt nanoparticles regulate the adsorption of oxygenated hydrocarbon intermediates, increasing the selectivity of the reaction. This work advances our understanding of catalyst design for methane conversion and the effective regulation of complex reaction pathways.

Preparation, structural property, and antioxidant activities of a novel pectin polysaccharide from the flowers of Hibiscus syriacus Linn.

Oxidative stress, triggered by an imbalance between reactive oxygen species (ROS) production and cellular antioxidant defense mechanisms, is implicated in various pathological conditions. Plant-derived polysaccharides have gained significant attention as potential natural antioxidants due to their biocompatibility, biodegradability, and structural versatility. This study focuses on the purification, structural characterization, and antioxidant activities of a novel pectin polysaccharide (HFPS) isolated from the flowers of Hibiscus syriacus Linn. HFPS was purified using anion-exchange chromatography. Its chemical composition, monosaccharide profile, molecular weight distribution, and structural properties were elucidated through various analytical techniques. HFPS exhibited a predominant acidic monosaccharide composition, with galacturonic acid as the major constituent, indicating its pectin nature. The free radical scavenging activity of HFPS against ABTS·, DPPḤ, and ·OH radicals was evaluated, demonstrating a positive correlation between its antioxidant capacity and concentration. Furthermore, HFPS effectively protected HepG2 cells against H2O2-induced oxidative stress by reducing ROS accumulation, modulating redox-related enzymes (Superoxide dismutase, Catalase, Glutathione peroxidase), and alleviating oxidative damage. Notably, HFPS upregulated the expression of antioxidant-related genes, including B-cell lymphoma-2 (Bcl-2), heme oxygenase 1 (HO-1), NAD(P)H quinone oxidoreductase 1 (NQO1), and nuclear factor erythroid 2-related factor 2 (Nrf2), while downregulating pro-apoptotic genes like Bcl-2-associated X protein (Bax) and Caspase-3. These findings suggest that HFPS exerts its antioxidant effects by modulating the Nrf2/HO-1 pathway and redox homeostasis. This study contributes to the understanding of the structure-function relationships and antioxidant mechanisms of HFPS, highlighting its potential applications as a natural antioxidant in various fields.

Methanesulfonic acid (MSA) and SO3 formation from the addition channel of atmospheric dimethyl sulfide oxidation.

The formation of methanesulfonic acid (MSA) from the dimethyl sulfide addition channel primarily proceeds via the reaction of methylsulfonyloxy radicals (CH3SO3) with H-atom donors, other than HO2 radicals. In competition with it, thermal decomposition of CH3SO3 results in SO3 generation. The MSA/SO3 ratio is driven by the temperature dependence of CH3SO3 decomposition.

Photocatalytic degradation of tetracycline antibiotics and elimination of N-nitrosodimethylamine formation potential by BiOCl/ZnIn2S4 heterostructure under visible-light irradiation.

Photocatalysis is an effective method for removing tetracycline antibiotics, which are important precursors to the potential carcinogen N-nitrosodimethylamine (NDMA). Herein, a BiOCl/ZnIn2S4 heterojunction was successfully synthesized using a simple hydrothermal method. This heterojunction was applied for the first time to degrade various tetracycline antibiotics and reduce NDMA formation potential (NDMA-FP) under visible-light irradiation. Characterization of surface morphology, crystal structure, chemical composition and photoelectrochemical properties revealed that the BiOCl/ZnIn2S4 heterojunction significantly improved light absorption, charge transport and carrier separation efficiency, thereby enhancing photocatalytic performance. The BiOCl/ZnIn2S4 catalyst achieved high degradation efficiencies of 88.0%, 90.7%, 88.7% and 91.7% for tetracycline, minocycline, chlortetracycline and doxycycline, respectively, within 60min of visible-light irradiation. Additionally, it exhibited the lowest NDMA-FP values of 1.5%, 3%, 0.9% and 1.4%, respectively. Radical trapping studies and EPR experiments identified •O2- and •OH radicals as the primary reactive species involved in the photocatalytic process. Analysis of the degradation intermediates and structure-activity relationships indicated that the variations in NDMA-FP were closely associated with the number of dimethylamine groups in the antibiotics and the stability of the resulting carbocations. Notably, the BiOCl/ZnIn2S4 catalyst presented satisfactory stability and positive tetracycline degradation in real antibiotic wastewater. Incorporating BiOCl/ZnIn2S4-loaded nonwoven fabric into a continuous-flow reactor efficiently degraded tetracycline in real wastewater under visible light. This work provides new insights on developing Z-scheme photocatalysts for the simultaneous degradation of various antibiotics and highlights their potential as commercially viable photocatalytic system.

Degradation and defluorination of C6F13 PFASs with different functional groups by VUV/UV-based reduction and oxidation processes.

Structural diversity can affect the degradability of per- and polyfluoroalkyl substances (PFASs) during water treatment. Here, three PFASs with different functional groups-C6F13-R, PFHpA, PFHxS, and 6:2 FTS-were degraded using vacuum ultraviolet (VUV/UV)-based treatments. While fully fluorinated PFASs-PFHpA and PFHxS-were degraded faster in the VUV/UV/sulfite reaction than in VUV/UV photolysis, VUV/UV photolysis was more effective for degrading 6:2 FTS by OH radicals produced through photolysis of water. PFCAs such as PFHxA, PFPeA, and PFBA were formed by VUV/UV photolysis of PFHpA and 6:2 FTS, but the PFCA formation was inhibited in the VUV/UV/sulfite reaction. The degradation of the three PFASs in the VUV/UV/sulfite reaction was mainly carried out by H/F and SO3•-/F exchange mechanisms, mediated by hydrated electrons (eaq-) produced in the reaction. During the VUV/UV/sulfite reaction, PFCA precursors were first formed as transformation products, which were further transformed into PFCAs by the following VUV/UV/H2O2 reaction, implying enhanced defluorination of three PFASs. Our results indicate that VUV/UV-based treatments can be an option for PFAS degradation and defluorination by combining advanced reduction and oxidation processes and utilizing both eaq- and oxidative radicals.