Study On The Control Of Electronic Structure Of Photocatalyst And Catalytic Oxidation Mechanism Of NO And Toluene

Nitric oxide?NOx?produced by fossil fuel and automobile exhaust combustion is the main precursor of photochemical smog.High concentrations of NOx from industrial emissions can be processed by conventional techniques,including physical adsorption,biological filtration,and thermal catalytic methods.However,these elimination of ppb-level NOx levels in indoor and outdoor atmospheric environments are still not economically and technically feasible,and the post-processing and regeneration problems of conventional technologies have not been solved.In addition,in the past few years,toluene has been used as a substitute for benzene,and organic solvents for adhesives and coatings are likely to be emitted from building materials into indoor environments,which have a major impact on today's life,for human health.Cause serious damage,such as sick building syndrome,and even environmental pollution such as photochemical smog.Light driven photocatalytic technology,as an environmentally friendly green technology,converts low-density solar energy into high-density chemical and electrical energy,oxidizing NOx to the final product NO₃^-under mild conditions,and NO₃^-is washed by water.Or the rainwater is transferred to the liquid phase and removed,while the toluene is completely mineralized into CO₂ and H₂O,which has broad application prospects in the treatment of low concentration air pollution.Oxidative removal of photocatalytic gas contaminants is a typical gas-solid phase catalytic reaction.The two steps of the reactants being adsorbed by the surface active center of the catalyst and reacted on the surface active center during the gas-solid phase catalytic reaction are the speed control steps.Directly restrict the efficiency of the reaction.Based on this,it is particularly important to adjust the electronic structure of the catalyst to enhance the adsorption and activation of the pollutant molecules on the catalyst surface.Therefore,in this paper,we modify the catalyst by three different electronic structure regulation schemes to enhance the adsorption and activation of the polluted gas molecules and O₂ and H₂O molecules.First,for the inorganic crystal material BiOBr,the performance of catalytically oxidizing NO is greatly improved by constructing an oxygen defect on the alternating exposed surface of?010?atoms and loading a plasma metal Bi element on the surface thereof.The charge transfer pathway on the Bi@defective BiOBr is significantly different from the charge transfer pathway on the original BiOBr.The Bi element is used both as an electron conductor and as an electron donor,which improves the electron hole separation efficiency.Oxygen vacancies provide an intermediate level to facilitate the transfer of the captured charge carriers to the adsorbed O₂ and produce·O₂^-free radicals.Due to the synergistic effect of Bi elemental and OVs in charge separation and O₂ activation,the photocatalytic performance of Bi@defective BiOBr is significantly improved.For the two-dimensional inorganic catalyst g-C₃N₄,a vertical charge channel is established by inter-layer doping of Sr atoms;the light absorption capacity and charge separation efficiency are accelerated.Most importantly,electronic localization was constructed on CN-Sr,resulting in uneven distribution of electrons on the surface of the CN layer.Eventually,O₂ molecules,NO contaminants and intermediates can exchange electrons with the catalyst and be activated to generate more free radicals and target products.Combined with in situ DRIFTS and DFT simulation results,we found that once NO and the intermediate are contacted on the surface of CN-Sr,it is adsorbed on the surface and depletes electrons into the low electron density region of CN-Sr.The electron exchange of the reactants on the surface of the photocatalyst gives these adsorbed materials a higher activation efficiency,which makes these intermediates more susceptible to destruction by reactive free radicals.Thus,NO can be selectively converted to the target product rather than toxic intermediates.The effect of oxygen defects on the electronic structure of photocatalytic materials is investigated by taking oxygen defects on the BiOCl?001?surface as an example to investigate the effect of oxygen defects on photocatalytic degradation of toluene.Oxygen deficiency can enhance the adsorption and activation of H₂O and toluene by local electrons,providing a new way to enhance the thermodynamic process of·OH formation and toluene oxidation.It has been experimentally confirmed that the methyl group will be oxidized and tend to open the benzene ring with benzoic acid on BOC and ring opening with benzyl alcohol on OVBOC.Most importantly,the ring opening efficiency of photocatalytic toluene degradation is well improved because the introduction of oxygen vacancies significantly reduces the activation of the reaction in the rate control step.Therefore,the toxic intermediate during the ring opening process can be immediately converted to the final product CO₂ with almost no accumulation of toxic products.Most importantly,the generation of possible toxic intermediates during photocatalytic reaction processes is typically neglected,even though it could result in the accumulation of secondary pollutants and decrease the photocatalytic performance.So,we conbine the DFT calculation and in situ DRIFTS spectra to better understand the mechanism of NO adsorption on photocatalysts,simulated the production of·O₂^-by calculating the O₂adsorption and thus elucidate the conversion pathways of photocatalytic NO oxidation.In addition,in the photocatalytic oxidation of NO and toluene,the accumulation of toxic intermediates not only inhibits the photocatalytic performance of the catalytic material,but also releases secondary pollution into the air,and the unclear contaminant conversion path restricts exploration of enhancing photocatalytic activity.Therefore,we combined experimental characterization,in situ DRIFTS and density functional theory calculations to clarify the intermediates and final products accumulated during the reaction,explored the formation of active radical species,and revealed the mechanism of photocatalytic oxidation of NO and toluene.Finally,a new method to increase photocatalytic activity and effectively inhibit intermediate toxic intermediates has been proposed.This study provides theoretical support for understanding the reaction mechanism of photocatalytic purification of pollutants and the regulation of toxic intermediates,and finally achieves safe and efficient purification of photocatalytic air pollution.