Gold core@CeO2 halfshell Janus nanocomposites catalyze targeted sulfate radical for periodontitis therapy

The sulfate radical (SO4•-), known for its high reactivity and long lifespan, has emerged as a potent antimicrobial agent. Its exceptional energy allows for the disruption of vital structures and metabolic pathways in bacteria that are usually inaccessible to common radicals. Despite its promising potential, the efficient generation of this radical, particularly through methods involving enzymes and photocatalysis, remains a substantial challenge. Here, we capitalized on the peroxidase (POD)-mimicking activity and photocatalytic properties of cerium oxide (CeO2) nanozymes, integrating these properties with the enhanced concept of plasma gold nanorod (GNR) to develop a half-encapsulated core@shell GNRs@CeO2 Janus heterostructure impregnated with persulfate. Under near-infrared irradiation, the GNRs generate hot electrons, thereby boosting the CeO2's enzyme-like activity and initiating a potent reactive oxygen species (ROS) storm. This distinct nanoarchitecture facilitates functional specialization, wherein the heterostructure and efficient light absorption ensured continuous hot electron flow, not only enhancing the POD-like activity of CeO2 for the production of SO4•- effectively, but also contributing a significant photothermal effect, disrupting periodontal plaque biofilm and effectively eradicating pathogens. Furthermore, the local temperature elevation synergistically enhances the POD-like activity of CeO2. Transcriptomics analysis, as well as animal experiments of the periodontitis model, have revealed that pathogens undergo genetic information destruction, metabolic disorders, and pathogenicity changes in the powerful ROS system, and profound therapeutic outcomes in vivo, including anti-inflammation and bone preservation. This study demonstrated that energy transfer to augment nanozyme activity, specifically targeting ROS generation, constitutes a significant advancement in antibacterial treatment.

Preparation of heterogeneous cation exchange membrane and its contributions in enhancing the removal of Ni2+ by capacitive deionization system

Capacitive deionization (CDI), an emerging method to eliminate ions from water at a low cost, has garnered significant interest in recent years. This study evaluates the implication of cation exchange resin loading on the membrane via the nonsolvent-induced phase inversion method. After determining the quantity of resins efficiently loaded on the membrane, it was subsequently utilized as a cation exchange membrane in the membrane capacitive deionization (MCDI) unit to examine the performance removal of Ni2+. The results show that the amount of resins influenced the membrane structure and significantly improved the efficiency of Ni2+ removal. The sulfonic acid group show a strong intensity directly proportional to the quantity of resins based on the FTIR measurement. In conjunction with the enhanced resin amount, ion exchange capacity and water content were increased. Simultaneously, there was an observed elevation in the water contact angle and the roughness of the membrane surface with increased resin amount. In the MCDI unit, membrane M20 (20% by weight resin) was employed to elucidate its roles in the CDI unit, encompassing an examination of various concentrations and flow rates, with Ni2+ utilized as a test contaminant. The results demonstrated that using membrane M20 in the MCDI (MCDI-M20) unit consistently exhibited higher adsorption levels than the CDI unit, reaching 19.80 mg g-1 ACC in the MCDI-M20 unit, while CDI unit achieved 10.27 mg g-1 ACC at 200 mg L-1 Ni2+ concentration and a flow rate of 10 mL min-1 at 1.2 V. Additionally, Ni2+ concentrations and flow rates in CDI system had an evident impact on the duration of adsorption due to the mechanisms of ions transport on the membrane. This study suggests that employing the prepared membrane in the MCDI unit enhanced the removal of Ni2+ from the solution, contributing to sustainable development goals.

Probing the activation mechanism of nitrogen-doped carbonaceous materials for persulfates: Based on the differences between peroxymonosulfate and peroxydisulfate

The activation processes of persulfates by metal-free nitrogen-doped carbonaceous material (NCM) remain unclear due to their complex structures and heterogeneous nature. On the other hand, from the perspective of persulfates, it is possible to clarify the reaction between persulfates and NCM by considering the differences in activation behaviors between peroxymonosulfate (PMS) and peroxydisulfate (PDS). Our study aims to compare the differences between NCM-PDS and NCM-PMS using a fully metal-free NCM as a model catalyst. Firstly, NCM-PDS was more efficient than NCM-PMS in degrading phenolic compounds (PCs). Secondly, the stoichiometric ratio between consumed persulfates and DCP removed in the NCM-PDS (0.73) is lower than in the NCM-PMS (1.08). Thirdly, PMS and PDS adsorb on NCM in different ways, suggesting that the peak O-O bond in PDS has blue shifted from 814 cm^-1 to 805 cm^-1, while that of O-O bond in PMS has shifted from 889 cm^-1 to 834 cm^-1. Additionally, the hydrogen bond between the phenolic group and oxidants plays a critical role in PCs degradation by NCM-PDS, exhibiting a stronger pH effect and higher kinetic isotope effects (KIEs) than NCM-PMS. A proton-coupled electron transfer process has been proposed for PCs degradation using NCM-PDS, and a scheme of reaction pathways has been provided for the NCM-PMS/PDS-PCs system. The study results provide a deeper understanding of the activation of persulfates by NCM, as well as a strategy for selecting oxidants.

Mechanistic Insights into Criegee Intermediate-Hydroperoxyl Radical Chemistry

The reaction between a Criegee intermediate and the hydroperoxyl radical (HO₂) is believed to play a role in the formation of new particles in the troposphere. Although the reaction has been previously studied in the gas phase, there are several knowledge gaps that still need to be filled. We simulated the reaction of anti-CH₃CHOO with HO₂ and HO₂-H₂O radical complexes in the gas phase at 0 K, which exhibited a low-barrier profile for water-containing systems and a barrierless profile for water-free systems. Moreover, the reaction was found to follow a proton-transfer mechanism, which challenges previous assumptions that the gas-phase reaction involves a hydrogen atom transfer. The HO₂ radical was found to mediate the Criegee hydration reaction in the gas phase. Metadynamics simulations further confirmed that the expected radical adduct formation between anti-CH₃CHOO and the HO₂ radical, as well as the HO₂- and H₂O-mediated reactions in the gas phase, followed a concerted mechanism. By combining constrained ab initio molecular dynamics simulations with thermodynamic integration, we quantitively evaluated the free-energy barriers at high temperatures. The barriers obtained for all three Criegee-HO₂ reaction systems were found to be temperature-dependent. We also compared the free-energy barriers of water-free and water-containing systems; the results revealed that water could hinder the reaction between the Criegee and HO₂ radical. These results suggest that HO₂ radicals may be involved in the formation of tropospheric radical adducts, and water molecules may also play important roles in the reactions of Criegee intermediates.

Fe/Co redox and surficial hydroxyl potentiation in the FeCo2O4 enhanced Co3O4/persulfate process for TC degradation

A magnetic FeCo₂O₄/Co₃O₄ nanocomposite was successfully synthesized by a facile hydrothermal method as an efficient activator for persulfate (PS) activation to degrade tetracycline (TC) in an aqueous solution. TC removal and mineralization efficiencies reached up to 91.63% and 43.57% in 120 min in the FCC-3/PS system, respectively. The mixed-valence of Fe/Co in the nanocomposite catalyst was beneficial for electrons transfer between Co and Fe elements and enhanced the redox circulation of Fe and Co in between divalent and trivalent. Surficial analysis and phosphate adsorption test confirmed the existence of -OH groups on the surfaces of FeCo₂O₄/Co₃O₄ nanocomposite. Fe/Co redox and surficial hydroxyl in the catalyst played significant roles in the TC potentiation degradation, which was contributed by the plenty of adsorbed -OH groups and excellent dispersity of FeCo₂O₄ in the FeCo₂O₄/Co₃O₄ composite. The sulfate radicals were major species followed by the hydroxyl radicals, and the surficial adsorbed hydroxyl made great contributions to radical generation. The cycling test and intermediate toxicity analysis indicated that the nanocomposite was considered stable and practicable in water treatment. This work demonstrated that the FeCo₂O₄/Co₃O₄ nanocomposite was an effective and environ-friendly catalyst towards PS activation for removing organic pollutants from water.

Autoxidation of Formaldehyde with Oxygen-A Comparison of Reaction Channels

The autoxidation of formaldehyde through initiation by triplet oxygen is studied via two initial steps: (1) H-atom abstraction and (2) ³O₂ addition reaction. The reaction energy profiles show that the reactions are thermodynamically and kinetically demanding. A comparison of the pathways of these initial reactions and the search for a less energy-demanding pathway is presented. The presence of a Brønsted acid has no effect on the energetics of the reaction, while the presence of a single water molecule catalyst enhances the initial reactions. The H-atom abstraction reaction from formaldehyde results in formyl and hydroperoxy radicals. These radicals on further reaction with the second equivalent of ³O₂ lead to a CO + 2HO₂ product channel. The ³O₂ addition reaction to formaldehyde results in a triplet biradical intermediate which further leads to performic acid, the precursor in the synthesis of carboxylic acids from aldehydes. In the presence of water molecules, performic acid is formed in a single kinetic step, and this leads to a CO₂ + OH + HO₂ product channel upon subsequent reaction with ³O₂ in a thermodynamically favorable reaction. The results show that the less established ³O₂ addition reaction to aldehydes is a viable route for autoxidation in the absence of purpose-built initiators, in addition to the well-established H-atom abstraction route.

Enhanced degradation of iohexol in water by CuFe2O4 activated peroxymonosulfate: Efficiency, mechanism and degradation pathway

Iohexol as an iodinated X-ray contrast agent is widely used, and it is the potential precursor for toxic iodinated disinfection by-products in the disinfection process. In this study, a series of CuFe₂O₄ catalysts were prepared by sol-gel method with different molar ratios of total metal cations to citric acid ([Meⁿ⁺]_T/CA) and employed as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the removal of iohexol. The catalysts were characterized by various technologies, and the effect of [Meⁿ⁺]_T/CA molar ratio on the catalysts' properties was explored. The CuFe₂O₄ synthesized with [Meⁿ⁺]_T/CA molar ratio of 1:1 showed the best catalytic activity to PMS, and 95.0% of 1.0 mg/L iohexol was removed within 15 min by using 50 mg/L CuFe₂O₄ and 20 mg/L PMS. The quenching experiment and electron spin resonance (ESR) spectra indicated the generation of SO₄^- and OH in the CuFe₂O₄/PMS system, and the quantity experiments revealed that the generation concentration of SO₄^- was ten times higher than that of OH. The generation mechanism of SO₄^- and ·OH were investigated by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) spectra. The effects of catalyst dosage, PMS and iohexol concentration on the removal of iohexol were studied, and various water matrix factors including solution pH, natural organic matter (NOM) concentration and inorganic ions were also considered. Based on the twelve intermediate products of iohexol detected by UPLC-QTOF/MS, the degradation pathway was proposed. The high catalytic activity and reusability of CuFe₂O₄ indicated that CuFe₂O₄ activating PMS is an effective and sustainable way for the treatment of iohexol.

A computational study of the HO2 + SO3 → HOSO2 + 3O2 reaction catalyzed by water monomer, water dimer and small clusters of sulfuric acid: kinetics and atmospheric implications

Herein, the reaction mechanisms and kinetics for the HO2 + SO3 → HOSO2 + 3O2 reaction catalyzed by water monomer, water dimer and small clusters of sulfuric acid have been...

Highly efficient removal of bisphenol A by a novel Co-doped LaFeO3 perovskite/PMS system in salinity water

Although it can effectively degrade refractory organic pollutants, advanced oxidation processes (AOPs) can be seriously interfered with the co-existing substance in salinity water. Herein, three-dimensional hierarchical cobalt-doped LaFeO₃ perovskites (LaCo_0.5Fe_0.5O₃) micron spheres composed of nano-rods were hydrothermally synthesized and applied to activate peroxymonosulfate (PMS) for degrading bisphenol A (BPA). Nearly 100% BPA was removed by LaCo_0.5Fe_0.5O₃/PMS system in presence of more than 50 mM Cl^- within only 2 min compared that of 30 min without Cl^-, which was attributed to reactive chlorine species (RCS) including Cl^• and HOCl with higher oxidation capacity. •OH and SO₄^•- produced by LaCo_0.5Fe_0.5O₃ activating PMS played crucial roles as the source of RCS in LaCo_0.5Fe_0.5O₃/Cl^-/PMS system. The synergistic effect between ROS and RCS promoted by the enhanced oxygen vacancies and the efficient redox recycling of Fe^III/Fe^II and Co^III/Co^II. Other anions like SO₄^2- and NO₃^- hardly affected the BPA degradation. BPA degradation efficiency was also improved either in a wide pH range or in the presence of natural organic matters in salty water. This work also demonstrated the potential application of FeCo bimetallic LaCo_0.5Fe_0.5O₃ activating PMS system for degradation of BPA or other organic micropollutants in seawater system.

Determination of the amine-catalyzed SO3 hydrolysis mechanism in the gas phase and at the air-water interface

New particle formation (NPF) involving amines in the atmosphere is considered an aggregation process, during which stable molecular clusters are formed from amines and sulfuric acid via hydrogen bond interaction. In this work, ab initio dynamics simulations of ammonium bisulfate formation from a series of amines, SO₃, and H₂O molecules were carried out in the gas phase and at the air-water interface. The results show that reactions between amines and hydrated SO₃ molecules in the gas phase are barrierless or nearly barrierless processes. The reaction rate is related to the basicity of gas-phase amines-the stronger the basicity, the faster the reaction. Furthermore, SO₃ hydrolysis catalyzed by amines occurs simultaneously with H₂SO₄-amine cluster formation. At the air-water interface, reactions between amines and SO₃ involve multiple water molecules. The reaction center's ring structure (amine-SO₃-nH₂O) promotes the transfer of protons in the water molecules. The formed ammonium cation (-RNH₃⁺) and the bisulfate anion (HSO₄^-) are present and stable by means of hydrogen bond interaction. The cluster formation mechanism provides new insights into NPF involving amines, which may play an important role in the formation of aerosols in some heavily polluted areas - e.g., those with a high amine concentration.

Atmospheric chemistry of the self-reaction of HO2 radicals: stepwise mechanism versus one-step process in the presence of (H2O)n (n = 1-3) clusters

The effects of water on radical-radical reactions are of great importance for the elucidation of the atmospheric oxidation process of free radicals. In the present work, the HO2 + HO2 reactions with (H2O)n (n = 1-3) have been investigated using quantum chemical methods and canonical variational transition state theory with small curvature tunneling. We have explored both one-step and stepwise mechanisms, in particular the stepwise mechanism initiated by ring enlargement. The calculated results have revealed that the stepwise mechanism is the dominant one in the HO2 + HO2 reaction that is catalyzed by one water molecule. This is because its pseudo-first-order rate constant (kRWM1') is 3 orders of magnitude larger than that of the corresponding one-step mechanism. Additionally, the value of kRWM1' at 298 K has been found to be 4.3 times larger than that of the rate constant of the HO2 + HO2 reaction (kR1) without catalysts, which is in good agreement with the experimental findings. The calculated results also showed that the stepwise mechanism is still dominant in the (H2O)2 catalyzed reaction due to its higher pseudo-first-order rate constant, which is 3 orders of magnitude larger than that of the corresponding one-step mechanism. On the other hand, the one-step process is much faster than the stepwise mechanism by a factor of 105-106 in the (H2O)3 catalyzed reaction. However, the pseudo-first-order rate constants for the (H2O)2 and (H2O)3-catalyzed reactions are lower than that of the H2O-catalyzed reaction by 3-4 orders of magnitude, which indicates that the water monomer is the most efficient one among all the catalysts of (H2O)n (n = 1-3). The present results have provided a definitive example that water and water clusters have important influences on atmospheric reactions.

Impact of water on the BrO + HO2 gas-phase reaction: mechanism, kinetics and products

The BrO + HO2 reaction, which participates in the cycle of ozone removal via BrOH formation, was explored both in the absence and in the presence of water using ab initio calculations. Two main sets of products, (i) HBr + O3 and (ii) BrOH + O2, are formed regardless of the presence of water, following a hydrogen abstraction mechanism. The HBr + O3 products are formed from the intermediate BrOOOH adduct, whereas BrOH + O2 are formed either from the intermediate OBrOOH adduct or via a barrierless hydrogen transfer from HO2 to BrO. Owing to the formation of molecular oxygen that can bear different spin configurations, the formation of BrOH + O2 products was examined both on the singlet and the triplet surfaces. Under relevant atmospheric temperatures and pressure, the formation of products (i) is energetically and kinetically less favorable than that of products (ii). The rate coefficient at 298 K for the HBr + O3 formation was determined to be 2.00 × 10-20 cm3 molecule-1 s-1, and found to decrease by 1-2 orders of magnitude when one or both reactants are clustered with water. For the formation of BrOH + O2, a rate coefficient of 2.21 × 10-11 cm3 molecule-1 s-1 is determined on both singlet and triplet surfaces in the absence of water. Though this rate coefficient slightly decreases for the hydrated reactions, the fractions of the reactants that are effectively complexed with water are not high enough to shift the overall BrOH + O2 formation rate. The current study further indicates that humidity plays a negligible role in ozone removal via the BrO + HO2 reaction.

Enhanced degradation of atrazine by nanoscale LaFe1-xCuxO3-δ perovskite activated peroxymonosulfate: Performance and mechanism

Cu-doped LaFeO₃ perovskite (LaFe_1-xCu_xO_3-δ, LFC_x) synthesized using a sol-gel method was introduced in the heterogeneous activation of peroxymonosulfate (PMS) for atrazine degradation. The obtained LFC_x catalysts were characterized by several technologies and the results showed that Cu was incorporated into the perovskites lattice successfully. In addition, the introduction of Cu resulted in the mixed valence state of Fe(III)/Fe(II) and Cu(II)/Cu(I) in perovskite structure. LaFe_0.8Cu_0.2O_3-δ (LFC_0.2) exhibited excellent catalytic activity and stability towards the degradation of atrazine. Atrazine (23 μM) was removed completely within 60 min in the presence of 0.5 g/L catalyst and 0.5 mM PMS. The efficient degradation was obtained when the initial pH ranged from 2 to 10. Sulfate radicals (SO₄^•-) and hydroxyl radicals (HO^•) generated during activation process were determined as the main reactive species based on the electron spin resonance (ESR) studies and radical quenching experiments. The enhanced catalytic activity derived from the lower valence state of Fe and Cu as well as the synergetic effect between them. A surface catalyzed-redox cycle between Fe(III)/Fe(II) and Cu(II)/Cu(I), along with surface hydroxyl groups (-OH), were all responsible for the decomposition of PMS. The oxygen vacancies could promote the chemical bonding with PMS and enhance the reactivity of Fe and Cu. The 12 transformation products were determined by LC-MS and the degradation mechanisms were further proposed, which involved five different pathways. The perovskite that possesses bimetallic active sites can be a promising catalyst for PMS activation towards the degradation of persistent organic pollutants with high-efficiency.

Influence of Ammonia and Water on the Fate of Sulfur Trioxide in the Troposphere: Theoretical Investigation of Sulfamic Acid and Sulfuric Acid Formation Pathways

Reaction of ammonia with SO₃ as a potential source of sulfamic acid in the troposphere has been investigated by means of electronic structure and chemical kinetic calculations. Besides, the hydrolysis reaction, which is known to be a major atmospheric decay channel of SO₃, has also been investigated. The catalytic effects of ammonia and water on both the reactions have been studied. Rate coefficients for all the studied reaction channels were calculated using the transition state theory employing pre-equilibrium approximation. Calculated rate coefficients for a number of catalyzed hydrolysis and ammonolysis processes were found to be much higher (by ∼10⁵ to ∼10⁹ times) than the gas kinetic limit at ambient temperature. With decrease in temperature because of negative temperature dependence of rate coefficients, that difference became even larger (up to ∼10¹⁶ times). Therefore, in order to remove the discrepancies, rate coefficients for all the studied reaction channels were calculated by means of the master equation. The results showed marked improvements, with only one channel showing a slightly higher rate coefficient above the gas kinetic limit. The rate coefficients for catalyzed channels obtained from the master equation also showed negative temperature dependence, albeit to a much smaller extent. The uncatalyzed ammonolysis reaction, similar to the corresponding hydrolysis, was found to be too slow to have any practical atmospheric implication. For both reactions, ammonia-catalyzed pathways have higher rate coefficients than water-catalyzed ones. Between hydrolysis and ammonolysis, the latter showed a higher rate coefficient. In spite of that, ammonolysis is expected to have negligible contribution in the tropospheric loss process of SO₃ because of large difference in concentration values between water and ammonia in the troposphere.

Elucidation of stoichiometric efficiency, radical generation and transformation pathway during catalytic oxidation of sulfamethoxazole via peroxymonosulfate activation

In this work, nano-bimetallic Co/Fe oxides with different stoichiometric Co/Fe ratios were prepared using a novel one-step solution combustion method. The nano-bimetallic Co/Fe oxides were used for sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation. The stoichiometric efficiencies of the as-prepared nano-bimetallic catalysts were calculated and compared for the first time. The radical generation was identified by electron paramagnetic resonance (EPR) as well as chemical quenching experiments, in which different scavengers were used and compared. The catalytic PMS activation mechanism in the presence of catalyst was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that besides SO₄•^- and •OH, •OOH was also detected in the PMS/CoFeO_2.5 system. Meanwhile, in addition to the previously proposed radical oxidation pathway, the results showed that SMX degradation also involved a non-radical oxidation, which could be verified by the degradation experiment without catalyst as well as the detection of ¹O₂. In the PMS activation process, cobalt functioned as the active site on CoFeO_2.5 while Fe oxide functioned as the adsorption site. The electron transfer mechanism was proposed based on the XPS and metal leaching results. Additionally, via the detection of transformation products, different SMX transformation pathways involving nitration, hydroxylation and hydrolysis in the PMS/CoFeO_2.5 system were proposed.

Catalytic effect of (H2O)n (n = 1–3) clusters on the HO2 + SO2 → HOSO + 3O2 reaction under tropospheric conditions

The HO₂ + SO₂ → HOSO + ³O₂ reaction without and with (H₂O)n (n = 1–3) have been investigated using CCSD(T)/CBS//M06-2X/aug-cc-pVTZ methods, and canonical variational transition state theory with small curvature tunneling.

Effects of water, ammonia and formic acid on HO2 + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step

Quantum chemical calculations at M06-2X and CCSD(T) levels of theory have been performed to investigate the effects of H₂O, NH₃, and HCOOH on the HO₂ + Cl → HCl + O₂ reaction. The results show that catalyzed reactions with three catalysts could proceed through two different mechanisms, namely a stepwise route and one elementary step, where the former reaction is more favorable than the latter. Meanwhile, for the stepwise route, a single hydrogen atom transfer pathway in the presence of all catalysts has more advantages than the respective double hydrogen atom transfer pathway. Then, the relative impacts of catalysts under tropospheric conditions were investigated by considering the temperature dependence of the rate constants and the altitude dependence of catalyst concentrations. The calculated results show that at 0 km altitude, the HO₂ + Cl → HCl + O₂ reaction with catalysts, such as H₂O, NH₃, or HCOOH, cannot compete with the reaction without a catalyst, as the effective rate constant with a catalyst is smaller by 2–6 orders of magnitude than the naked reaction within the temperature range 280–320 K. The calculated results also show that at altitudes of 5, 10 and 15 km, the effective rate constant of the HCOOH-catalyzed reaction increases obviously with an increase in altitude. At 15 km altitude, its value is up to 9.63 × 10⁻¹¹ cm³ per molecule per s, which is close to the corresponding value of the reaction without a catalyst, showing that the contribution of HCOOH to the HO₂ + Cl → HCl + O₂ reaction cannot be neglected at high altitudes. The new findings in this investigation are not only of great necessity and importance for elucidating the gas-phase reaction of HO₂ with Cl in the presence of acidic, neutral and basic catalysts, but are also of great interest for understanding the importance of other types of hydrogen abstraction in the atmosphere.

The effects of acidic (FA), neutral (WM) and basic (AM) catalysts on the energetic and kinetic aspects of the HO₂ + Cl reaction have been studied. At 298 K, the catalytic order of FA, WM and AM is WM > FA > AM.

Catalytic effect of (H2O) n (n = 1-3) on the HO2 + NH2 → NH3 + 3O2 reaction under tropospheric conditions

The effects of (H2O) n (n = 1-3) clusters on the HO2 + NH2 → NH3 + 3O2 reaction have been investigated by employing high-level quantum chemical calculations with M06-2X and CCSD(T) theoretical methods, and canonical variational transition (CVT) state theory with small curvature tunneling (SCT) correction. The calculated results show that two kinds of reaction, HO2⋯(H2O) n (n = 1-3) + NH2 and H2N⋯(H2O) n (n = 1-3) + HO2, are involved in the (H2O) n (n = 1-3) catalyzed HO2 + NH2 → NH3 + 3O2 reaction. Due to the fact that HO2⋯(H2O) n (n = 1-3) complexes have much larger stabilization energies and much higher concentrations than the corresponding complexes of H2N⋯(H2O) n (n = 1-3), the atmospheric relevance of the former reaction is more obvious with its effective rate constant of about 1-11 orders of magnitude faster than the corresponding latter reaction at 298 K. Meanwhile, due to the effective rate constant of the H2O⋯HO2 + NH2 reaction being respectively larger by 5-6 and 6-7 orders of magnitude than the corresponding reactions of HO2⋯(H2O)2 + NH2 and HO2⋯(H2O)3 + NH2, the catalytic effect of (H2O) n (n = 1-3) is mainly taken from the contribution of the water monomer. In addition, the enhancement factor of the water monomer is 10.06-13.30% within the temperature range of 275-320 K, which shows that at whole calculated temperatures, a positive water effect is obvious under atmospheric conditions.

Ab initio kinetics of the HOSO2 + 3O2 → SO3 + HO2 reaction

The detailed kinetic mechanism of the HOSO₂ + ³O₂ reaction, which plays a pivotal role in the atmospheric oxidation of SO₂, was investigated using accurate electronic structure calculations and novel statistical thermodynamic/kinetic models. Explored using the accurate composite method W1U, the detailed potential energy surface (PES) revealed that the addition of O₂ to a HOSO₂ radical to form the adduct (HOSO₄) proceeds via a transition state with a slightly positive barrier (i.e., 0.7 kcal mol^-1 at 0 K). Such a finding compromises a long-term hypothesis about this channel of being a barrierless process. Moreover, the overall reaction was found to be slightly exothermic by 1.7 kcal mol^-1 at 0 K, which is in good agreement with recent studies. On the newly-constructed PES, the temperature- and pressure-dependent behaviors of the title reaction were characterized in a wide range of conditions (T = 200-1000 K & P = 10-760 Torr) using the integrated deterministic and stochastic master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) rate model in which corrections for hindered internal rotation (HIR) and tunneling treatments were included. The calculated numbers were found to be in excellent agreement with literature data. The sensitivity analyses on the derived rate coefficients with respect to the ab initio input parameters (i.e., barrier height and energy transfer) were also performed to further understand the kinetic behaviors of the title reaction. The detailed kinetic mechanism, consisting of thermodynamic and kinetic data (in NASA polynomial and modified Arrhenius formats, respectively), was also provided at different T & P for further use in the modeling/simulation of any related systems.

Role of the (H2O)n (n = 1–3) cluster in the HO2 + HO → 3O2 + H2O reaction: mechanistic and kinetic studies

Upon incorporation of the catalyst (H₂O)_n (n = 1–3) into the reaction HO₂ + HO → H₂O + ³O₂, the catalytic effects of water, water dimer, and water trimer mainly arise from the contribution of a single molecule of water vapor.

Heterogeneously catalyzed persulfate with a CuMgFe layered double hydroxide for the degradation of ethylbenzene

CuMgFe layered double hydroxide (CuMgFe-LDH) was successfully synthesized and characterized as an efficient catalyst of persulfate (PS) for the degradation of ethylbenzene. Under the conditions of 0.2gL^-1 CuMgFe-LDH and 4.0mmolL^-1 persulfate at pH 7.6, the degradation efficiency of 0.08mmolL^-1 ethylbenzene was 93.7% with TOC removal efficiency of 65.2% in 24h, and the concentration of Cu leached into the solution was as low as 0.095mgL^-1 after the reaction. The reuse of CuMgFe-LDH showed that the catalyst was highly stable after 5 recycles. Electron Spin Resonance (ESR) test and free radical quenching experiment indicated that SO₄^- and OH radicals were the dominant species accounted for the degradation of ethylbenzene in the CuMgFe-LDH/persulfate system. Catalytic mechanism of the formation of a complex of Cu(II)O₃SOOSO₃^2- and the subsequent redox cycle of Cu(II)/Cu(III) accounted for the generation of radicals was proposed.

Ammonia Catalyzed Formation of Sulfuric Acid in Troposphere: The Curious Case of a Base Promoting Acid Rain

Electronic structure calculations have been performed to investigate the role of ammonia in catalyzing the formation of sulfuric acid through hydrolysis of SO₃ in Earth's atmosphere. The uncatalyzed process involves a high activation barrier and, until date, is mainly known to occur in Earth's atmosphere only when catalyzed by water and acids. Here we show that hydrolysis of SO₃ can be very efficiently catalyzed by ammonia, the most abundant basic component in Earth's atmosphere. It was found, based on magnitude of relative potential energies as well as rate coefficients, that ammonia is the best among all the catalysts studied until now (water and acids) and could be a considerable factor in formation of sulfuric acid in troposphere. The calculated rate coefficient (at 298 K) of ammonia catalyzed reaction has been found to be ∼10⁵-10⁷ times greater than that for water catalyzed ones. It was found, based on relative rates of ammonia and water catalyzed processes, that in troposphere ammonia, together with water, could be the key factor in determining the rate of formation of sulfuric acid. In fact, ammonia could surpass water in catalyzing sulfuric acid formation via hydrolysis of SO₃ at various altitudes in troposphere depending upon their relative concentrations.

Heterogeneous activation of peroxymonosulfate by amorphous boron for degradation of bisphenol S

Recently, tremendous efforts have been devoted to developing carbon-based metal-free catalysts as an alternative to metal-based catalysts for remediation of emerging contaminants. However, further investigations have demonstrated that the durability of carbocatalysts is poor. Therefore, it is extremely desirable to seek a novel metal-free catalyst with high efficiency and superb stability. Herein, we first discovered that amorphous boron (A-boron) can be used as a metal-free catalyst for peroxymonosulfate (PMS) activation to produce free radicals for effective degradation of bisphenol S (BPS), which is a newly-occurring estrogenic endocrine-disrupting chemical. It exhibited outstanding catalytic activity and superior stability as comparing to metal-based and metal-free carbon-based catalysts. Moreover, many other typical organic pollutants in water such as bisphenol F, sulfamethoxazole, rhodamine B and methyl orange can also be effectively decomposed in A-boron/PMS oxidative system. The effects of reaction parameters on BPS degradation were systematically investigated. The catalytic oxidation mechanism was proposed. The intriguing catalytic feature of A-boron discovered in this study will provide new opportunities for the future development of A-boron based materials with promising applications in water remediation.

Sulfate Radical-Mediated Degradation of Sulfadiazine by CuFeO2 Rhombohedral Crystal-Catalyzed Peroxymonosulfate: Synergistic Effects and Mechanisms

Copper-iron bimetallic oxides have shown great potential for powerful radical production by activating peroxides. In this work, CuFeO2 rhombohedral crystals (RCs) were synthesized and used as heterogeneous catalysts for peroxymonosulfate (PMS) activation under various conditions. Sulfadiazine, a widely used veterinary sulfonamide, was used as a target pollutant to evaluate the efficiency of this combination. The results showed that of all the catalysts tested, the CuFeO2 RCs had the greatest reactivity. Under conditions of 0.1 g L(-1) CuFeO2 RCs and 33.0 μM PMS, the nearly complete degradation of sulfadiazine occurred within 24 min. A synergistic catalytic effect was found between solid Cu(I) and Fe(III), probably due to the accelerated reduction of Fe(III). The two activation stages that produced different radicals (hydroxyl radicals followed by sulfate radicals) existed when solid Cu(I) was used as the catalyst. The CuFeO2 RCs had a higher PMS utilization efficiency than CuFe2O4, probably because the Cu(I)-promoted reduction of solid Fe(III). A total of 10 products were identified, and their evolution was explored. On the basis of the evidence of oxidative product formation, we proposed four possible pathways of sulfadiazine degradation.

Can a single water molecule really affect the HO2 + NO2 hydrogen abstraction reaction under tropospheric conditions?

During the HO₂ + NO₂ reaction, hydrogen abstraction by a single water molecule not only changes the branching ratio of HONO and HNO₂ formation, but also introduces different features with respect to the naked reaction, acting as a reactant that leads to the production of HNO₃.

H2CO3→ CO2+ H2O decomposition in the presence of H2O, HCOOH, CH3COOH, H2SO4and HO2radical: instability of the gas-phase H2CO3molecule in the troposphere and lower stratosphere

Carbonic acid decomposition of potential atmospheric significance.