Study On The Construction Of TiO₂(B)/anatase Heterogeneous Junction Photocatalyst With Stabilized Surface And Ion Doping

Photocatalysis is considered as a promising technology for solving the energy and environmental crisis.Among all the semiconductor materials,titanium dioxide has become the most widely used photocatalyst material due to its stable chemical properties,strong redox ability,corrosion resistance,non-toxicity and low cost properties.Among four crystal types of titanium dioxide,TiO2(B)shows a unique crystal structure,which can be used in photocatalysis,electrocatalysis and lithium ion batteries.However,the lower crystallinity and the non-visible light absorption ability greatly restrict its application.In this thesis,we focus on the fabrication of TiO2(B)/anatase junction at higher temperature,which can enhance the crystallinity of the material.Furthermore,co-doping strategy was introduced to expand the light absorption range of TiO2(B)-based material.The details are as follows:1.As a metastable phase structure,TiO2(B)is prone to transform to the stable anatase or rutile phase at high temperature and the low crystallinity of TiO2(B)is usually formed at low temperature.Therefore,both of the above two concerns restrict its application in photocatalysis.In this research,we found that an appropriate amount of HF can inhibit the phase transformation process from TiO2(B)to anatase.XRD patterns and Raman spectra showed that when 0.3wt%HF was added prior to the calcination,a large amount of TiO2(B)can be maintained even at 750℃,while HF-free sample or the sample with excess amount of HF can only obtain anatase phase.As evidenced by SEM,TEM and HRTEM,TiO2(B)/anatase heterophase junction was observed in the sample with the addition of 0.3wt%HF,which exhibited the highest photocatalytic activity both for pollution degradation and hydrogen production.XPS results confirmed that the F element was only physically adsorbed on TiO2.The phase structure controlled by the addition of HF was proposed to be the crucial factors for the high activity.The phase transformation mechanism was finally revealed by DFT calculations,which demonstrates that the lower surface energy of TiO2(B)(100)with the adsorption of fluorine anions results in the retarded phase transformation process.2.The application of titanium dioxide is limited to some extent by its wide band gap(3.2 eV),which requires ultraviolet irradiation for photocatalytic activation.Because ultraviolet light accounts for only a small part(5%)of the solar energy compared with visible light(45%),the change of the optical response of titanium dioxide from ultraviolet light to visible spectrum will have far-reaching positive effects on the practical application of materials.N doping was considered to the most effective meaning for enhancing the visible light absorption ability.However,high temperature calcination for N doping could destroy the structure of TiO2(B)and affect the bulk doping.Based on our previous results,we introduced some HF previous to the N doping process.It could not only stabilize the structure but also slightly etch the surface of TiO2(B),which can both promote the uniform doping of N.Our results show that,the addition of N can effectively enhance the visible light absorption ability.Furthermore,co-existence of N and F elements can obviously promote the photocatalytic activity compare with single doping samples,showing a synergetic effect on the structure modification and the photocatalytic performance.