Construction Of TiO₂(B)/anatase Heterogeneous Junction Structure And Its Application In Photocatalysis

TiO₂ is one of the most widely used photocatalysts among many semiconductor photo catalytic materials with its chemical stability,strong ability of oxidation-reduction reaction,corrosion resistant,non-toxic and low cost.TiO₂（B）is the fourth crystal form besides anatase,rutile and brookite.In this thesis,we manily focus on the phase transformation process,construction of the hetero-phase junction,the charge carriers’behavior,and expanding the light absorption range of TiO₂（B）.Detail work is as follows:1.Fabrication of heterojunction is one of the most effective strategies to enhance photo catalytic performance of semiconductor photocatalysts.Here,TiO₂（B）/anatase nanowires with interface heterostructure were prepared through a three-step synthesis method,including hydrothermal treatment,H+ exchange reaction and anneal process.The phase structure of the nanowires in the bulk and on the surface during anneal process was monitored by XRD patterns,and UV-Raman spectra.SEM and TEM also indicate that the TiO₂（B）nanowires are partially collapsed and transform into anatase during the anneal process and the hetero-phase junction structure is formed simultaneously.According to the phase structure together with morphology data,the phase transformation mechanism was proposed.Photocatalytic activity was evaluated by hydrogen production and pollutant degradation assays.The optimized structure of photocatalyst is containing 24%of TiO₂（B）in the bulk and 100%of anatase on the surface.The charge behaviors during the photocatalytic process indicating that the hetero-phase junction structure in the bulk is responsible for the high efficiency of charge separation and transportation,the anatase on the surface take charge for the high surface reaction activity.2.Annealing the sample at different temperatures is not the only way to construct the hetero-phase junction in the material.Here,we found that the introduction of the phase transfer inhibitor can also be a good choice and the hetero-phase junction can be obtained at higher temperature.TiO₂（B）/anatase hetero structure nano wires can be obtained by introducing hydrofluoric acid before annealing.The photocatalyst samples annealed at different temperatures were characterized by XRD and SEM.At the same time,the photocatalytic activity was aslo be tested.The results showed that,in addition of 3%hydrofluoric acid,the activity of the photocatalytic hydrogen production decreased,while the activity of photocatalytic degradation of RhB increased.It is speculated that,the crucial property of material for reduction and oxidation reactions are quit different.3.Ultraviolet light only accounts for less than 5%in the solar spectrum,while visible light accounts for 45%of the total solar energy.The band gap of titanium dioxide is around 3.2 eV,and it can only absorb ultraviolet light of less than 387nm.So this greatly limits the use and development of titanium dioxide photocatalysts.In order to broaden the range of light absorption response,two methods have been investigated in this paper.One is introducing N elements into TiO₂（B）using TiN as precusor,the other is combining g-C3N4 and TiO₂（B）.The characterization results show that,N element was successfully introduced into TiO₂（B）with an expanded light absorption up to 800 nm.The surface area of the catalyst was also increased with the N doping and the activity for RhB degradation was greatly increased.On the other hand,although the combination of g-C3N4 and TiO₂（B）did not show an obvious visible light absorption due to the limited content of g-C3N4,but it can promote the photocatalytic activity by the introduction of g-C3N4/TiO₂（B）heterojucntion.