Regulation Of Oxygen Vacancy Defects In Bismuth- And Cerium-based Semiconductor Oxides And Their Photocatalytic NO_x Removal Performance

Oxygen vacancies(OVs)defect had become a focus in the atmospheric governance,degradation of liquid pollutants,photolytic hydrolysis,carbon dioxide reduction and other photocatalytic fields,due to its great effects on adjusting band structure and strong interaction with gas molecule(oxygen molecules and gas pollutant molecules).The method of constructing OVs in different materials is different,including,1.calcination with inert atmosphere(N2,Vacuum environment et al.);2.calcination with reducing gas(H2,CO et al.),3.chemical reduction(NaHB4,KBH4 et al.)and 4.ions doping.Therefore,we can choose the most suitable OVs construction method for different catalyst systems.In this thesis,BiOI,(BiO)2CO3(BOC)and CeO2 were selected as photocatalysts to study the effect of OVs in these different materials on NOx removal.The advantages and disadvantages of photocatalysts with rich-OVs are discussed.During the catalysis process of the OVs-BOC and NaHB4-CeO2-x photocatalysts,poor stability and high production of NO2 limited their practical application.In order to overcome the shortcomings while maintaining the advantages of OVs defect in the photocatalysis,the metal-OVs coupling method is obtained.This thesis focuses on the following aspects of the construction of OVs defects:(1)Using the ion doping that replacing the Bi3+in the lattice of BiOl crystal by Zn2+to induce the OVs defects into the BiOI photocatalyst.The morphology of as-prepared Zn-BiOI is a microsphere that composed of innumerable ultra thin nanosheets.The Zn2+dopant promotes the formation of OVs defect,which can optimize the band structure of BiOI and suppress the growth of BiOI along with c-axis to promote the generation of ultra-thin nanosheets.3%Zn-BiOI photocatalyst can oxides 53.6%of NO to bi-NO3-or br-NO3-under the excitation of visible light.Moreover,this super oxidation capacity for NO can be maintained during the cycle experiment which including five photocatalytic experiments.The Zn-BiOI sample prepared by heterovalent ion doping method showed super oxidation and stability.It was further confirmed by the OVs-BiOI sample that was prepared by ultraviolet irradiation.Finally,theoretical calculations,electrochemical and in situ FTIR tests certificated that this great photocatalytic performance can be attributed to the positive effect of OVs on photogenerated carrier recombination,and special adsorption and oxygen activation.(2)A new type of OVs-BOC photocatalyst was prepared by calcination method under the N2 surroundings to research the effect of OVs during the NOx photocatalytic process.The results showed that OVs defect enhanced the optical absorption of BOC catalyst,as well as the transfer and separation capabilities.The NO removal rate was promoted upto 46.3%.However,there are some drawbacks during this process that are weak catalytic stability and poor selectivity catalysis.In the photocatalytic process of BOC,the formation of NO2 is 23 ppb and the shrinking of catalytic performance is 24.6%after 4th photocatalytic process.Series of Bi-based photocatalysts were prepared via controlling of calcination temperature.Compared with the OVs-BOC catalysts,BiO/OVs-BOC has the best photocatalytic performance,due to the synergy between OVs defect and metallic Bi,which brought the great transfer and separation capabilities of photogenerated charges,a wide spectral response range of compound.In the process of NOx,removal over BiO/OVs-BOC sample,54.4%of NO was removed and only 3 ppb of NO2 was formed.The possible pathway of photocatalytic NO removal and the formation and repression mechanism of NO2 are supported by the trapping tests,ESR experiments,in situ FTIR tests and simulation calculation.(3)The Ce element has two stable valance states:+3 and+4.Thanks to this characteristic,NaHB4-CeO2-x and Pd0/CeO2-x composite photocatalysts can be prepared under the reduction of NaHB4.The phase information of CeO2 is conducted by ac-TEM,and the EELS mapping prove the precence of Ce4+@Ce3+core@shell of NaHB4-CeO2-x.Moreover,the XPS,ESR,Raman and PL and Uvs-Vis DRS tests described the presence and the optical feature of OVs defect in the CeO2 crystal.The simulation calculation gave the detail about absorption energy of NO,NO2 and O2 on the surface of(100)and(111)of CeO2 with OVs or without OVs.In additional,the contribution of OVs on the band structure of(100)and(111)of CeO2 also be calculated.NaHB4-CeO2-x.has a better activity(51.0%removal rate of NO)than CeO2-x.But the formation of NO2 is nonnegligible(39.2 ppb).The synergy between OVs defect and metallic Pd0 optimized the selective photocatalysis of NaHB4-CeO2-x.The possible pathway of photocatalytic NOx oxidation is supported by the trapping tests,ESR experiments,in situ FTIR tests and simulation calculation.