Research On Singlet Oxygen Formation Mechanism And Photodegradation Performance Of Kaolin-based Composite Structure Photocatalyst

The essence of photochemistry is that electrons could transfer after the object absorbing light.Thereinto,when the semiconductor absorbs the light,the electrons at the top of the valence band could transfer to the bottom of the conduction band,and then the conduction band electrons and the valence band holes,which can act as redox reaction sites,could be formed.It is the phenomenon of photocatalysis.In photocatalysis,in addition to electrons and holes,excitons affected by Coulomb force,are also a kind of photogenerated carriers.Excitons exist objectively,especially in low-dimensional semiconductors and strongly confined systems.Considering the existence of excitons,not only the charge transference,but also the energy transfer process of excitons is the basic principle of photocatalytic reactions.Due to the existence of the exciton energy transfer process,singlet oxygen can be directly generated,which could become a new mechanism explanation for photodegradation phenomenon.In this paper,based on the above argument,and combined with the abundant kaolin mines in Inner Mongolia Autonomous Region which the surface engineering could be employed,two kinds of photocatalyst which could be used in the area of photodegradation are designed.What’s more,the mechanism of singlet oxygen generation and photodegradation is also discussed thoroughly.The research contents are as follows:（1）Two-dimensional flake-shaped WO₃ was prepared by hydrothermal method,and NaBH₄ was used to adjust the surface oxygen vacancies of WO₃.It was loaded on Kaolin,the multifunction carrier,which has a large number of hydroxyl groups on its surface,could promote the photodegradation reaction.The 134-WO_3-x@Kaolin catalyst can degrade the high concentration TC solution（50 mg/L）to a low concentrate in a short time.It is a result of the singlet oxygen generated by the exciton energy transfer process in the system.（2）The high temperature calcination method was used to adjust the active sites of ZIF-8 and change its light absorption performance.And it was also loaded on Kaolin,which has the same use as the first system.The color method and EPR were used to detect the reactive oxygen species,singlet oxygen,that can be produced by the catalytic system in this chapter.Through the analysis of the data of the UV-Visible diffuse reflectance spectrum,the UPS energy spectrum and the fluorescence spectrum,the mechanism,being different from the previous work,could be found.And the process of photo-generated singlet oxygen and photodegradation of methylene blue could be explained.Both of the two chapters in this paper are significantly important to the study of the mechanism of photocatalytic degradation.