Investigation On The Active Sites Construction And Photocatalytic NO Removal Performance Of Bismuth Molybdate Materials

With the continuous increase of population,the problem of resource shortage and environmental pollution have become increasingly serious.Among them,NO_x pollution in the air has adverse effects on environmental safety and human health.Since nitric oxide（NO）accounts for the majority of NO_x pollution in the air,it is of great significance to develop a method which is effective in NO removal.The traditional NO removal method is complex,large energy consumption,high economic cost,and can’t remove low concentration NO.Photocatalytic NO removal method has attracted wide attention due to its green,high efficiency and the ability to remove low concentration NO.Among the catalysts used for photocatalytic NO removal,bismuth molybdate shows unique advantages because of its strong absorption ability of visible light,and layered structure is beneficial to photogenerated carriers transport and separate.However,bismuth molybdate lacks effective catalytic active sites,so it is necessary to adopt modification methods to construct active sites on bismuth molybdate for efficient photocatalytic NO removal.Based on these considerations,this study takes bismuth molybdate as the research object,and constructs defect active site and metal active site on bismuth molybdate by alkali etching and metal doping respectively,and studies the specific role of these active sites in photocatalytic NO removal by a series of characterization methods.The main research contents are as follows:1.In combination with the dual advantages of crystal plane control and defect construction,{001}facets exposed bismuth molybdate was synthesized to increase the exposure ratio of[MoO₄]^2-layer on the catalyst surface,and then the[MoO₄]^2-layer was selectively etched by alkali etching method to construct“Mo-O”defects active site.The results of catalytic activity showed that the NO removal rate of 50 mg bismuth molybdate containing defect active site（BMO-OH）reached 47%,which was 2.1 times of bismuth molybdate without defect（BMO）（22%）.The removal rate of NO was improved without significantly increasing the formation of toxic intermediate NO₂.ICP-MS,EPR,XPS and other characterization proved that the defect was located in the[MoO₄]^2-layer.The difference between the photoelectric properties and the interface properties of the materials were investigated.The characterization results showed that the“Mo-O”defects have significantly increased the carriers transmission and separation efficiency,and greatly enhanced the adsorption and activation of O₂ and NO.On this basis,we further adopt active species detection experiment,sacrificing reagents for active species experiment and in-situ infrared experiment,comparative study the photocatalytic removal NO mechanism of BMO and BMO-OH,It was found that BMO-OH had a better ability to activate O₂ due to the excellent function of activating O₂ and localized photogenerated electrons by defect.The·O₂^-and ¹O₂ obtained by activating O₂ and localized photogenerated electrons by defect played an important role in improving NO removal rate.2.Combining the advantages of morphology control and metal doping,using CTAN as surfactant and adding Fe³⁺ion in the hydrothermal synthesis process,Fe-doped thin bismuth molybdate nanosheets were synthesized,the optimal Fe doping content was 0.1%.The photocatalytic activity experiment results of the samples showed that thinner nanosheets could significantly improve the removal rate NO,but at the same time,it would produce high concentration of toxic intermediate NO₂.Further doping Fe in the thin nanosheets had little effect on NO removal rate,but could significantly reduce the generation of toxic intermediate NO₂.Under the optimal doping amount,30 mg BMO（CTAN）-0.1Fe could remove about 50%of NO under illumination,while the yield of NO₂ was only 40%of BMO（CTAN）.The photocatalytic NO removal mechanism of BMO（CTAN）and BMO（CTAN）-0.1Fe were compared by active species detection experiment,sacrificing reagents for active species experiment and in-situ infrared experiment.It was found that BMO（CTAN）-0.1Fe had stronger ability to activate H₂O to produce·OH,and·OH played an important role in the conversion of NO₂ to NO₃^-.This part of the research successfully explained the roles of thin structure and doped metal site in NO removal.The former enhances the conversion of NO to intermediate NO₂,while the latter enhances the conversion of NO₂ to NO₃^-.