Theoretical And Experimental Research On TiO₂(B)-based Photocatalytic Materials

Semiconductor photocatalysis is a potential technology because its photoinduced electron in semiconductors performs a solar conversion into electrical or chemical energy to tackle the world energy problems and environmental pollutions.Unfortunately,the photocatalytic activity of TiO2 is limited by its low quantum efficiency of photocatalysis,which results from the rapid recombination of photogenerated electron-hole pairs and wide band gap.Many efforts have been made to improve the photocatalytic activity of the TiO2-based materials.Recently,although the photocatalytic technology has made great progress in both experiment and industry,there are still some bottlenecks need solved,resulting that this promising technology has not been applied in a large scale industry.The most problem is a lack of fundamental understanding of the photocatalytic mechanism.In this thesis,we investigate the intrinsic photocatalytic mechanism of TiO2-based photocatalytic material in both experiment and theory.Experimentally,single crystal Na0.9Mg0.45Ti3.55O8 nanosheets were synthesized by using a simple hydrothermal method and their photocatalytic performances are explored.Theoretically,DFT was performed to systematically investigate the surface relaxation,surface stability,electronic structure of TiO2(B)and Na2MgTi7O16.This combined study with theory and experiment provides an innovative idea to understand photocatalytic activity of the TiO2-based materials.The main works of this thesis are as follows:Electronic structure and photocatalytic properties of TiO2(B):The electronic densities of TiO2(B)bulk and surface were calculated by MedeA-VASP.We performed a systematical investigation of the surface relaxation,surface stability,electronic structure of the TiO2(B).A systematic energy calculation for the three surfaces adsorbed with nonmetallic and metallic atoms was performed to explore the stability of the adsorbed surfaces.The planes become more stable after adsorbing nonmetallic elements.Light-induced charge transport within Na0.9Mg0.45Ti3.55O8:The photocatalytic activities of Na0.9Mg0.45Ti3.55O8 have been studied.The XRD,SEM,TEM and UV-vis results show that the single crystal Na0.9Mg0.45Ti3.55O8 nanosheets were obtained.The methylene blue solution was used as the target contaminant,and light with different wavelengths was applied to study the NMTO degradation.The surface potential of the sample was measured under illumination with different wavelengths.In addition,Au/NMTO samples were prepared by photoreduction deposition method to investigate the photocatalytic activity.Sodium(Na)and magnesium(Mg)doping of TiO2(B)have been studied to simulate the electronic structure of single crystal Na2MgTi7O16 through DFT calculations.The computational simulation of crystal morphology by the calculated surface energy agrees well with NMTO crystal morphology in experiment.According to the calculated redox potentials of different surfaces,the transfer of electrons and holes between the surfaces is analysized.