Modification Of TiO₂ And Its Mechanism Of Photocatalytic Removal Of NO_x

As a widely studied photocatalyst,titanium dioxide(TiO2)has been proven to have degradation effects on inorganic and organic substances and to be able to kill a variety of bacterias.The advantages of TiO2 in terms of cheap and easy availability and chemical stability are well known,but its defects of poor response to visible light and easy compounding of photogenerated carriers are the hot issues that need to be addressed in current research.Therefore,in order to improve the efficiency of TiO2 photocatalysis,reasonable modification methods need to be studied.The common methods for catalyst modification include ion doping,semiconductor compounding,noble metal deposition and photosensitization.In addition,these methods can also be used in combination with each other to achieve better results.The research of efficient and simple methods to modify the photocatalytic activity of TiO2 is important for the development of photocatalytic applications.In this study,a series of modified samples were prepared using tetrabutyl titanate as a raw material for the preparation of TiO2 by hydrolytic calcination and sol-gel methods,respectively.The NO removal was used as the evaluation criterion for the photocatalyst activity,and the physical-chemical and optical properties of the catalysts and the characteristics of the semiconductor materials were investigated in detail with the basic characterization of the materials.By combining the structure of heterojunction with the introduction defect,and by combining the carrier load with the introduction defect,the best samples were obtained with NO removal activity of about 70%,and the details of the study are as follows.(1)TiO2 samples were prepared from TBOT by hydrolysis calcination method.The addition of HCl at the hydrolysis stage promoted the phase transformation of TiO2 to form homogeneous heterojunction.Meanwhile,annealing at 300℃ under argon atmosphere can form interfacial oxygen vacancies and surface oxygen vacancies in the heterojunction TiO2 can be formed.The characterization by XRD,Raman,XPS,TEM and EPR demonstrated the generation of phase transition and the successful introduction of oxygen vacancies in the samples.The photocatalytic experiments reveal that surface oxygen vacancies and interfacial oxygen vacancies have synergistic effects in the generation of photocatalytically reactive oxygen species(ROSs),which can control the distribution and utilization of photogenerated carriers in heterojunction TiO2.TPD test results show that surface oxygen vacancy can enrich O2,and transfer electrons to O2 on anatase surface,and convert to ·O2-and 1O2.Interfacial oxygen vacancies enable the transfer of photogenerated electrons to anatase,leaving photogenerated holes in rutile.These holes in the rutile part have high oxidation potential,which can better oxidize H2O(or OH-)molecules to ·OH and also oxidize ·O2-to 1O2.Finally,it was proved through the capture experiment that the main reason for the improvement of NO removal activity was that the modified sample could produce more reactive oxygen species.(2)A series of TiO2 loaded diatomite samples were prepared by sol-gel method using TBOT as the raw material of TiO2 and diatomite as the carrier of photocatalyst.In this experiment,the effect of acid leaching pretreatment of diatomaceous earth on the activity of the samples and the role of argon atmosphere annealing to introduce defects on the catalysts were investigated.After the study to select the optimum reaction temperature and composite ratio,the samples were analyzed in detail in terms of material composition,structural characterization,and physicochemical properties in order to investigate the reasons for the increased activity of the samples.Such as XRD,SEM,XPS and solid EPR were done in detail to analyze the composition of the material,the successful loading of the composite and the successful introduction of defects.In this section,the experiments use the porous material diatomaceous earth as a carrier to solve the problem of serious TiO2 agglomeration phenomenon and construct a synergistic system of adsorption-degradation with photocatalyst to improve the efficiency of photocatalytic reaction.The nature of the porous material enables it to enrich water and oxygen in the air and enhance the ability of the catalyst to produce active oxygen.Meanwhile,the introduction of defects into the photocatalyst promotes the photogenerated electron transfer in the catalyst,thus improving the overall photocatalytic activity of NO removal.