Construction And Performance Control Of Titanium Dioxide-based Heterostructure Photocatalytic Materials

Energy and environmental issues have collected many attentions from the human society.As a typical n-type semiconductor material,titanium dioxide(TiO2)is widely used in photocatalytic degradation of organic pollutants,hydrogen production,CO2 reduction and other fields because of its special energy band structure and physical and chemical properties.However,its wide band gap(3.2 eV)which only responds to the ultraviolet part(4%)of sunlight,low carrier separation efficiency(≤10%),and weak redox capability,severely restrict its further appliation.For photodegradation of organic pollutants with TiO2,the method of semiconductor heterogeneous coupling were used in the present work to produce high performance TiO2 based photodegradation materials,which includes the following parts:(a)fabricate and optimize the heterogeneous interface of in-situ grown TiO2/ZrTiO4 by adjusting their content,and thus to improve the separation efficiency of charge carriers;(b)construct a multilayer porous and photonic crystal structure to achieve effective adjustment of light utilization;(c)build the R-TiO2/A-TiO2 Z-scheme heterojunction by doping with non-metallic B element,and improve the material’s redox potential and the types of active free radicals through controlling the phase content and energy band structure.Finally,high-performance titanium dioxide-based heterostructure photocatalytic materials are obtained,which also provides ideas for the performance optimization of various semiconductor photocatalytic materials.The results obtained are summarized as follows:(1)The type Ⅱ TiO2/ZrTiO4/SiO2 heterojunction photocatalytic material was prepared by in-situ TiO2/ZrTiO4/SiO2 heterogeneous phase generation by sol-gel method.The results show that the construction of TiO2/ZrTiO4 heterojunction effectively improves the photocatalytic efficiency,and the introduction of SiO2 can greatly increase the specific surface area of the material,which leads to the excellent adsorption performance.In the dark reaction,the adsorption efficiency of rhodamine B(RhB)reached 60.7%,and the photocatalytic degradation efficiency reached 95%after 60 min visible light irradiation.After three cycles of reaction,the adsorption and degradation efficiency of the material showed no obvious decrease.On this basis,the template method was further used,and polystyrene spheres were used as the template to construct type Ⅱ TiO2/ZrTiO4/SiO2 heterojunction photocatalytic materials with different microstructures(multilayer pore structure,photonic crystal structure).The results show that the construction of a multilayer pore structure can further effectively increase the specific surface area of the material,and more active sites can be exposed on the surface for subsequent redox reactions.At the same time,the construction of the inverse opal photonic crystal structure with the slow photon effect,effectively improved the utilization rate of visible light,thus further improve the photocatalytic performance of the material.(2)The Z-scheme R-TiO2/A-TiO2 heterogeneous junction photocatalysis material was constructed by doping TiO2 with nonmetallic B element.The experimental results show that element B enters the anatase TiO2 lattice,reduces the cell volume,and promotes the transformation from anatase phase to rutile phase to form R-TiO2/A-TiO2 heterojunction;at the same time,it leads to the formation of Ti3+ ions,which can form impurity energy level and effectively regulate the energy band structure.As the B doping content is 10%,the valence band potential of the material was the highest(+1.68 eV)and the produce of·OH radical was enhanced.After 90 min of visible light irradiation,the photocatalytic degradation rate reached 95%and the photocatalytic degradation rate was 0.033 g·min-1.The mechanism analysis shows that the carrier migration between R-TiO2/A-TiO2 heterojunction was determined to be fit for the Z-scheme heterojunction mode,and the Z-scheme R-TiO2/A-TiO2 heterojunction is successfully constructed.(3)The Z-scheme/Ⅱ type R-TiO2/A-TiO2/ZrTiO4 double heterojunction photocatalysis material was constructed by doping TiO2/ZrTiO4 with nonmetallic B element.The results show that with the increasing of B doping content,the phase content of R-TiO2 increased gradually,and the photocatalytic performance of the material had a trend of increase first and then decrease.As the molar ratio of B:Zr:Ti was 1:2:10,the mass ratio of R-TiO2/A-TiO2 was 0.066.The photocatalytic degradation rate of the material reached 97%under visible light irradiation for 90 min,and the photocatalytic degradation rate was 0.038 g·min-1.By introducing R-TiO2/A-TiO2 heterojunction through B doping with the existence of type Ⅱ A-TiO2/ZrTiO4 heterojunction,the further increaseing of redox potential difference and stronger redox ability were obtained.Under visible light irradiation,it can produce more active free radicals,promote the subsequent redox reaction,hence improve the photocatalysis properties of the material.