Active Sites Construction On Bismuth-Based Material And Investigation Of Its Performance For Photocatalytic NO Removal

Nitrogen oxides is a type of exhaust gas pollutants with serious hazards.Due to the high energy consumption of conventional removal methods,photocatalysis is regarded as a new green and energy-saving technology.Unlike traditional Ti O₂ photocatalysts,the unique structure of bismuth-based materials facilitates the separation of photogenerated carriers;more importantly,the light absorption range of which can be extended to visible light.However,shortcomings of bismuth-based materials such as lack of active sites on the surface,wide band gap,easy recombination of photo-generated charges,and low light utilization efficiency,restrict their application in NO removal.Based on this,bismuth-based materials bismuth subcarbonate and bismuth oxychloride are selected in this article as models,and modifications like bismuth-enrichment treatment,crystal face exposure,oxygen vacancy introduction,etc.,had been done to enhance carrier transmission and increase active sites for small molecules.Moreover,influence on photocatalytic NO removal activities are explored.The specific research contents are as follows:1.The photocatalytic activity of bismuth-based material Bi₂O₂CO₃ is improved by introducing oxygen vacancies.Specifically,carbon-doped bismuth oxychloride is synthesized by a hydrothermal method using glucose as a carbon source,whcih is further calcined in Ar/H₂O atmosphere to obtain Cl-doped Bi₂O₂CO₃ material.Characterizations such as EPR and XPS proved that the presence of water vapor during the calcination process successfully introduced oxygen vacancies on the surface of the material.The activity test found that the photocatalytic NO removal rate of Bi₂O₂CO₃ material reached 60%,which was 2.14 times of the material before modification,and had a lower residual ratio of intermediate product NO₂.Subsequently,through the results of the quenching experiment of active species,it is speculated that singlet oxygen is the most important active species in the process of NO removal reaction.Through TPD and radical capture experiments,it is found that the introduction of oxygen vacancies promotes the chemical adsorption of NO and O₂ molecules by Bi₂O₂CO₃,and generates more singlet oxygen,thereby greatly improving the photocatalytic NO removal performance of the material.2.The structure of bismuth oxychloride can be adjusted through the selection of different carbon chain agents to improve the photoelectric performance of the material and further improve the photocatalytic NO removal activity.It was found that using sodium oleate as the carbon source and adjusting the p H of the system to 12 for hydrothermal synthesis,carbon-doped bismuth-rich bismuth oxychloride Bi₁₂O₁₇Cl₂ can be obtained.It is then calcined in Ar/H₂O atmosphere to remove carbon and obtain pure Bi₁₂O₁₇Cl₂.XRD characterization observed that the exposure ratio of van der Waals gap facet is high,which is conducive to the adsorption and activation of O₂.EPR,DRS,XPS and other tests have found that calcination under water vapor atmosphere can introduce a large amount of oxygen vacancies on the surface of the material,and confirm the removal of carbon.Photocatalytic NO oxidation experiments found that the NO conversion rate of the modified Bi₁₂O₁₇Cl₂ material under illumination was 63%,which was 2.37 times of carbon-doped Bi₁₂O₁₇Cl₂,and the residual rate of by-product NO₂ was extremely low（7.4%）.Through the quenching experiment of active species,it is found that singlet oxygen plays a very important role.Through a series of experiments such as photocurrent test,photoluminescence spectroscopy（PL）,electrochemical impedance spectroscopy（EIS）,radical trapping experiments,etc.,it is found that the carrier mobility of the material after introducing oxygen vacancies and regulating the structures is greatly improved and more reactive oxygen species can be generated,which creates the excellent NO removal performance.