Preparation Of Composite Photocatalysts And Its Application In Photocatalytic Removal Of Nitrogen Oxides

With the development of economy and industrialization,air pollution has become more serious in our country,which has attracted the atte ntion of the government and the society.As the main pollutants in air pollution,nitrogen oxide?NOx?has caused huge damage to the environment.These pollutans also do harm to human health.Nowadays,numerous effective approaches have been developed to purify air pollution for the high concentration exhaust gases discharged from the thermoelectric industry.However,these technologies are limited to deal with nitrogen oxides which are produced at high concentration,high temperature and fixed emission sources.A large part of NO_x in air pollution comes from vehicle exhaust and garbage incineration.These oxides of nitrogen are of low concentration,and the emission source is changeable,which is difficult to handle them using the above techniques.Photocatalytic technology has been applied to remove nitrogen oxides,which obtains a number of merits,such as less damage on environment,low energy consumption,mild reaction conditions,and easily absorbed reaction products.Thus this environmentally friendly technology holds great promising in practical application.Meanwhile,Photocatalytic technology is also considered as the most ideal environmental purification technology in the world today,by the environmental protection circles.However,most single-component photocatalysts suffer from the disadvantages of low catalytic efficiency,low conversion efficiency of light energy and easy deactivation which restricts its large-scale production and application.Considering the above shortcomings upon single-component photocatalysts,our work foucses on improving the stability and activity of the photocatalysts and improving their efficiency,expecting that the photocatalysis technology can be applied to air pollution control earily.The main contents are as follows:1.A series of photocatalysts of SrCO₃,SrTiO₃,and SrCO₃ decorated Sr TiO₃were prepared via one step in-situ pyrolysis method,and then were used for the photocatalytic removal of NO.The results indicate that the presence of SrCO ₃ can not only improvethe photocatalytic activity of Sr TiO₃,but also inhibit the deactivation of SrTiO₃ during NO removal.In the photocatalytic process,the photogenerated electrons in conducting band?CB?of Sr TiO₃ could migrate to the CB of SrCO₃,accelerating the carrier separation.Meanwhile,the strong O₂ adsorption on the SrCO₃surface would increase the production of·O₂^-.Moreover,the presence of SrCO₃ could also increase the surface acidity of Sr TiO₃,which thus increase the NO adsorption and facilitate the oxidatio n of NO.The above experimental data suggested that SrCO ₃functions as surface deposited noble metals without the shortcomings caused by noble metals.Overall,the prepared SrCO₃ holds promising as environmentally friendly and economic substitutes to noble metals.2.A series of g-C₃N₄/SrSO₄ composite photocatalysts with different mass ratio were prepared by grinding calcination.The structure,element distribution and microstructure of the mentioned samples were analyzed by XRD,energy spectrum analysis,scanning electron microscope and transmission electron microscope.The optical properties and the produced free radicals of photocatalysts were analysised by UV-vis diffuse reflectance spectroscopy,fluorescence spectroscopy,time-resolved electron spin resonance and electrochemical characterization methods.A new photocatalytic mechanism of photocatalytic NO removal under visible light irradiation was proposed based on the capture experiments and ion chromatography analysis.Meantime,the cytotoxicity tests and bacteriostasic activity were also performaned and the results showed that the catalysts have excellent bio-performance.Based on above results,we envision that a certain amount of SrSO ₄ in g-C₃N₄ can improve its surface area,increase the absorption and enhance electron transfer properties and provide more active sites.In addition,the absence of Sr²⁺is beneficial to the separation and transfer of photogenerated electrons and holes,thus improving the photocatalytic activity.At the same time,the produced Sr⁺can promote the production of·OH through Fenton reaction.The increase of·OH can enhance the oxidation and photocatalytic activity of the catalyst.3.A series of TiO₂/g-C₃N₄ composites with different mass ratios were prepared using urea and butyl titanate as raw materials.The photocatalytic properties of the composites were investigated.The structure,morphology and photoelectric properties were also characterized by powder X-ray diffraction?XRD?,scanning electron microscopy?SEM?and electrochemical workstation.The optical properties of the catalysts were investigated by ultraviolet visible diffuse reflectance spectroscopy?UV-vis DRS?and fluorescence spectrometer.In addition,the photocatalytic mechanism of the removal of NO under visible light was further explored.