Preparation And Characterization Of Oxygen Deficient Materials

With the rapid economic development,environmental pollution has become a major problem today,and catalytic technology has made great progress in environmental governance.Among them,photocatalysis is a relatively simple and effective way,using light energy to decompose organic pollutants into substances such as carbon dioxide and water,or to precipitate some gaseous pollutants such as nitrogen and sulfur.However,researchers still face difficulties and challenges,such as the rapid recombination of photo-generated electron-hole pairs in the catalyst,the low quantum efficiency,and the easy generation of reaction intermediates on the surface to prevent the further reaction and affect the catalyst activity.However,these problems can be well overcome by the modification of catalyst materials,such as doping ions,composite catalysts et al,which proves that photocatalysis still has great prospects.In the process of photocatalysis using solar energy,most of the light energy is converted into heat to increase the surface temperature of the catalyst,which will excite the bound electrons in the shallow energy level and generate hot carriers,and at the same time,the electrons in the defect energy level will tend to transition to the conduction.The band is then transferred to the surface,enabling more electrons to participate in the photocatalytic reaction,while the high temperature helps the molecular activation to participate in the catalytic reaction.Photothermal catalysis,which combines the light and thermal contributions of sunlight,can utilize the solar spectrum more efficiently,has become a rapidly growing new research field,and deserves in-depth study.In this study,a heterojunction with large specific surface area and oxygen defect photothermal combined catalytic performance was synthesized,which can efficiently improve the electron-hole separation ability,and at the same time make the photo-generated electron-hole pair have strong redox ability.It has a synergistic catalytic effect in catalytic nitrogen fixation and degradation of gaseous pollutants.In addition,we prepared photocatalysts with different oxygen defects to explore the possible mechanism of the effect of oxygen defect concentration on catalyst degradation efficiency.It is believed that this research can promote the development and progress of semiconductor catalysis.1.Photothermal combined photothermal degradation of gaseous pollutants and nitrogen fixation by oxygen-deficient Ce O2/Cr2O3The composite catalyst CeO2/Cr2O3 was prepared after drying,calcining and grinding by adjusting the mass ratio of cerium nitrate hexahydrate and chromium nitrate nonahydrate,and using the sol-gel method to dissolve the two.According to XRD phase,SEM morphology and XPS chemical valence analysis,it can be seen that Ce O2 and Cr2O3 are successfully combined and contain a large number of oxygen defects.The data of PL spectrum,photocurrent and impedance show that the photoelectron separation efficiency and transfer ability of the composite samples are improved compared with the previous ones,and oxygen defects play the role of impurity energy levels in them,storing electrons and inhibiting the recombination of carriers.The N2adsorption-desorption curve shows that the composite sample has a large specific surface area,with a maximum area of 119.1 m2·g-1,which can provide enough adsorption active sites for the reaction.It can be seen from the M-S test that Cr2O3 is a p-type semiconductor material,and Ce O2 is an n-type semiconductor material.When the two are combined,a heterojunction can be constructed to improve the electron separation efficiency,and the composite heterojunction has a strong redox ability.The catalytic test shows that the sample has excellent photothermal synergistic degradation of gaseous pollutants and nitrogen fixation.In situ DRIFTS revealed the specific reaction steps of photocatalytic and thermal catalytic degradation of gaseous pollutants and nitrogen fixation,as well as the influencing factors that limit the catalytic reaction,which provides a certain reference value for in-depth understanding of the photothermal catalytic mechanism.2.Study on photocatalytic properties of oxygen deficient Bi2MoO6 materialsIn this work,Bi2MoO6 was prepared by a sol-gel method,and then the material was annealed in a reducing atmosphere.The color of the sample changed from yellow to brown with the increase of temperature,which was caused by the formation of oxygen defects in Bi2 Mo O6 due to the detachment of lattice oxygen.XRD analysis showed that the oxygen-deficient samples were successfully prepared without phase change.The analysis of PL spectrum,photocurrent,impedance and theoretical calculation shows that oxygen defects change the sample structure to a great extent,and the generation of oxygen defect impurity energy levels reduces the energy required for electronic transitions,which is more conducive to photo-induced charge separation and transport,providing abundant oxygen active adsorption site generates a large number of superoxide radicals（·O2-）to participate in the catalytic oxidation reaction.The photocatalytic activity characterization shows that the optimal annealing temperature is100 °C,at which the photocatalytic activity of isopropanol is increased by 1.97 times.The changes of chemical bonds of adsorbed molecules on the surface of Bi2 Mo O6during the degradation of gaseous isopropanol were investigated by in situ DRIFTS,so as to provide an experimental basis for its catalytic degradation steps.