The Construction And Photocatalytic Properties Of TiO₂ Heterostructure（Phase） Junction

With the development of industry and society,the energy crisis and environmental pollution have become two major problems that human beings need to solve.Finding effective ways to control pollution and absorb solar energy and achieving a clean and sustainable development model have become the common goals of modern society.Semiconductor photocatalysis technology is a green technology with great application potential in solving these two problems.As one of the most popular photocatalyst,Titanium dioxide（TiO₂）has the advantages of environmental friendliness,low cost,and chemical stability.It is widely used in research on the treatment of wastewater,CO₂reduction and hydrogen production.However,the wide band gap of～3.2 e V and rapid charge（holes and electrons）recombination have severely hindered the photocatalytic application of TiO₂.Therefore,it is crucial to narrow down its band gap and accelerate the separation of photogenerated hole-electron（e^--h⁺）pairs.Therefore,a variety of strategies have been used to shorten the band gap of TiO₂ and accelerate the carrier transfer rate.In this thesis,from the perspective of extending the photoresponse range and improving the photocatalytic efficiency of TiO₂,the samples were synthesized by hydrothermal method,the codoping of metallic and nonmetallic elements,semiconductor compounding and changing the phase composition were used to modificated of TiO₂.Finally,N/Ti³⁺co-doped TiO₂ heterostructure（phase）junctions with improved visible light response and photocatalytic properties were synthesized.The main research contents are as follows:（1）N/Ti³⁺co-doped TiO₂ heterojunctions comprising anatase and brookite phases were synthesized by hydrothermal method using TiCl₃ and ethylenediamine as precursors.The structure,crystallinity,chemical state and optical properities of the as-prepared samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,high-resolution transmission electron microscopy（HR-TEM）,X-ray photoelectron spectroscopy（XPS）and UV–Vis diffuse reflectance spectroscopy.The synthesized heterojunction nanomaterials contained N,Ti³⁺and Ov.The results show that the volume of ethylenediamine play significant influence on the mass ratio of anatase and brookite,and the structure,optical,morphology and properties of the prepared TiO₂ were further influenced by the mass ratio of TiO₂（A）and TiO₂（B）.Under visible light irradiation,the sample with the mass ratio of anatase to brookite is 59:41,which shows the best visible light response and photocayalytic performance.（2）The TiO₂ heterojunctions were prepared by hydrothermal synthesis of TiN.The effects of initial p H and temperature on the crystal phases of TiO₂ heterojunction were studied.On the basis of this,the light absorption properties and the visible light photocatalytic degradation properties of each sample were examined.The results show that when p H=3 and 220°C,the visible light absorption and photocatalytic activity of TiO₂heterojunction are the highest.（3）A series of N/Ti³⁺codoping triphasic TiO₂/g-C₃N₄composites were obtained by a simple hydrothermal treatment of g-C₃N₄ and TiN.During the hydrothermal process,TiN was completely converted to N/Ti³⁺codoping triphasic TiO₂ and g-C₃N₄can be activated while heterojunctions was formed between them.The effect of different molar ratios of N/Ti³⁺codoping triphasic TiO₂ and activated g-C₃N₄on optical properties and photocatalytic activities of the resulting heterojunctions were investigated systematically.A red-shift of absorption edge and enhanced absorption intensity were observed for the N/Ti³⁺codoping triphasic TiO₂/g-C₃N₄composites in comparison with N/Ti³⁺codoping triphasic TiO₂ and pristine TiO₂.The photoelectrochemical and electrochemical impedance spectra measurements revealed that the prepared heterojunctions with optimal g-C₃N₄/TiO₂molar ratio（0.025:1）showed more efficient electrons-holes separation,which also exhibited the highest visible-light photocatalytic activity for methylene blue,Rhodamine B,phenol,and levofloxacin degradation.The triphasic TiO₂/g-C₃N₄ heterojunctions and the existence of Ti³⁺/N doping levels improved the charge separation efficiency and extended the light absorption range,thus enhancing the photocatalytic activity of TiO₂.This study develops a novel structure of TiO₂-based heterojunction photocatalysts by simple one step hydrothermal approach and and reveals an efficient route to improve the photocatalytic activity of TiO₂.