Investigation Of The Mechanisms Of Atmospheric Homogeneous And Heterogeneous Oxidation As Well As Liquid Phase Catalytic Hydrogenation And Dechlorination Of Chlorophenol

Chlorophenols（CPs）are a very important group of compounds that are widely distributed in the environment and are closely linked to the formation of secondary organic aerosols（SOA）and persistent organic free radicals（PFRs）.The study explores the reaction mechanisms of CPs in the atmospheric gas phase and the heterogeneous reactions at the atmospheric air-particle and air-water interfaces to provide a scientific and theoretical basis for further traceability and pollution control of SOA and PFRs,and pollution control and emission reduction of precursors.The study uses a computational chemistry approach to investigate the homogeneous and heterogeneous reaction mechanisms of CPs by selecting 2-chlorophenols（2-CPs）,2,4,6-trichlorophenols（2,4,6-TCPs）and pentachlorophenols（PCPs）as model compounds,and to design catalytic reduction schemes for CPs pollutants represented by 2-CPs.The study mainly includes exploring the mechanism and kinetics of the gas-phase reaction of CPs oxidation by·OH（hydroxyl radical）,resolving the variability of the mechanism and kinetics of CPs oxidation by·OH at the air-particle interface,elucidating the potential influence of the air-water interface on the mechanism and kinetics of CPs oxidation,designing photocatalytic hydrodechlorination catalysts for the detoxification of CPs.The study aims to provide a theoretical basis for the generation of SOA and PFRs from CPs in the atmosphere at the molecular level,and to design and prepare an efficient photocatalytic hydrodechlorination catalyst for CPs to achieve the reductive detoxification of CPs pollution.Based on DFT and TST theories,the reaction mechanism and kinetics of·OH oxidation of CPs in the gas phase were investigated.It was found that the oxidation of CPs by·OH mainly contributes to the formation of PFRs and can significantly promote the formation of PFRs with increasing temperature.At 298 K,the rate constants for the oxidation of chlorophenols by·OH were in the order of 2-CPs>2,4,6-TCPs>PCPs,and the reaction branching ratios for the oxidation of 2-CPs,2,4,6-TCPs and PCPs by·OH through the H-abstraction reaction pathway to generate PFRs were 0.29,0.97 and0.99,the results indicate that the oxidation of 2,4,6-TCPs and PCPs by·OH mainly generated PFRs,and 2-CPs generated HOMs via the·OH-addition reaction with subsequent autocyclisation of alkoxy radicals（RO·）,which mainly contributed to the SOA formation.The results of the ecotoxicity evaluation indicated that the main products of·OH oxidation of chlorophenols were more toxic to aquatic organisms than chlorophenols.To address the impacts of humidity and the air-particle interface on the mechanism and kinetics of·OH oxidized CPs,a study on the reaction mechanism and kinetics of·OH oxidation of CPs at the air-particle interface was carried out.The results showed that the main reaction channel of 2-CPs in the gas phase was the·OH-addition reaction channel,and the main reaction change of 2-CPs through hydrogen bonding with the air-particle interface(Si₃O₁₀H₈)was the H-abstraction reaction,the main reaction channels of 2,4,6-TCPs and PCPs in both the gas phase and the air-particle interface were dominated by the H-abstraction reaction channel.Thus,chlorophenols with different chlorine substituents modify the oxidation mechanism at the air-particle interface by forming hydrogen bonds of different strengths with the air-particle interface.The kinetics of·OH oxidation of CPs were studied based on TST theory.The results show that at 298 K,the·OH oxidation rates of 2-CPs,2,4,6-TCPs and PCPs at the gas-phase and air-particle interface are not significantly different at the same order of magnitude level.The calculated H-abstraction and the branching ratios of the H-abstraction and·OH-addition rates to the total rate constants were calculated,and the branching ratio for the direct oxidation of 2-CPs to PFRs via the H-abstraction reaction at the interface was 0.59,the branching ratios of·OH-addition at the phenolic hydroxyl sites of 2,4,6-TCPs and PCPs were as high as 0.79 and 1.00,respectively.To produce the intermediates T-IM1 and P-IM1 were predominant.In the gas phase and at the air-particle interface,T-IM1 and P-IM1 can generate PFRs through intramolecular dehydration by bridging atmospheric water molecules,indicating that atmospheric humidity promotes the generation of PFRs from CPs.To explore the complex chemical reactions of CPs at the air-water interface,this study explores the microstate patterns of three typical CPs（2-CPs,2,4,6-TCPs and PCPs）at the air-water interface to reveal the influence of the air-water interface on the mechanism and kinetics of the CPs oxidation reaction.The umbrella-shaped sampling results show that with the increase of the number of chlorine atom substitution,the change of the system free energy of CPs from the gas phase through the gas-water interface region to the water phase region gradually increases,and so does the free energy of dissolution that CPs needs to overcome.The potential barriers for the hydration of the three CPs with water molecules at the air-water interface are in the order of 2-CPs<2,4,6-TCPs<PCPs.CPs undergo hydration to form ionic CPs^-which enter the liquid phase and undergo single electron transfer reactions with·OH to form PFRs.By comparing the energy barriers for the hydration of CPs at the air-water interface with those for the oxidation with·OH,it was found that 2-CPs and 2,4,6-TCPs were more likely to undergo hydration,whereas PCPs were more likely to undergo hydroxylation,indicating that the air-water interface not only facilitated the formation of PFRs from CPs,but also changed the reaction mode of CPs.By calculating the apparent rate constants(k_app),the ionic state reaction of CPs plays a major contribution to the reaction of CPs with·OH k_app,indicating that CPs generate PFRs at the air-water interface and in the liquid phase mainly through oxidation of the formed ionic CPs.The generated PFRs open the ring to decompose into reactive chlorine species（RCS）,which react with atmospheric·Cl,NO₂ and O₂ to form phosgene,peroxynitrate chloroformate and peroxychlorocarbonyl radicals respectively.Toxicity calculations revealed that the resulting chlorine-containing compounds were developmentally toxic,irritantly toxic to skin mucosa and severely irritating to eye mucosa.A photocatalytic hydrodechlorination strategy with 2-CPs as a typical CPs pollutant was proposed to achieve reductive detoxification of CPs contamination.Simulations using density flooding theory（DFT）indicate that Pt,Pt-g-C₃N₄,and Pt/WP breakdown H₂O to H⁺,while also delivering electrons to decrease H⁺to atomic hydrogen（H*）.The calculations show that Pt/WP has the lowest H₂O decomposition potential and H⁺is most readily accessible to electrons on the Pt/WP surface to generate H*.The order of the adsorption energy of H*on the catalyst surface is Pt-g-C₃N₄>Pt/WP>Pt.The above calculations presume that the coupling of WP and Pt-g-C₃N₄would act as an efficient catalyst for hydrodechlorination.Therefore,in this study,Pt-WP/g-C₃N₄ catalysts were prepared experimentally,which could effectively reduce2-CPs to less toxic phenols with 92.0%conversion.Electron spin resonance spectroscopy and H*capture experiments also demonstrated that the coupling of WP and Pt-g-C₃N₄ promoted the production and utilisation of atomic hydrogen（H*）.Ab initio molecular dynamics simulations showed that the Pt-WP/g-C₃N₄ interface has good resistance to catalyst deactivation,which promotes H*production and improves the effectiveness of Pt-WP/g-C₃N₄ in reducing 2-CPs,enabling stable and efficient reductive detoxification of CPs pollutants.