The Synthesis,Phase Transformation And Luminescence Properties Of Titanium Dioxide In Different Morphologies

Titanium dioxide(TiO2)is an excellent semiconductor which is widely used in solar cells and photocatalysts because of its good photostability.There are several phases of TiO2 such as anatase,rutile,baddeleyite,and α-PbO2.All these phases have unique physical and chemical properties,and undergo phase transformation among each other under certain conditions.Therefore,it is important to understand phase transformation,such as how the pressure and temperature affect the phase transformation sequence and the structural and optical properties of the resulted product.Such study is the key to design new materials and explore novel applications.In this paper,the high-pressure phase transformation of TiO2 with different morphologies was studied by synchrotron X-ray diffraction.The luminescence properties and electron structure of titanium dioxide were studied by X-ray absorption near-edge structure and X-ray excited optical luminescence.The main contents of the paper include:(1)Phase transformation of TiO2 hollow microspheres and solid microspheres under high pressure.The hollow and solid microspheres were prepared by a one-step hydrothermal method.The phase transformation under high pressure was monitored in situ Raman spectroscopy and synchrotron X-ray diffraction.The result shows that the the phase transition pressure in TiO2 hollow spheres is higher than that in TiO2 hollow spheres.High pressure will destroy the hollow structure first and then induce the phase transition.The morphology changes of TiO2 hollow spheres and solid spheres provide an intuitionistic evidence for shape transformations in spherical materials under high pressure.(2)Phase transformation of TiO2 nanoflower under high pressure.F-doped TiO2 nanoflowers were prepared by a hydrothermal method.In situ Raman spectroscopy indicates that F-doped titanium dioxide nanoflower transformed from anatase phase toα-PbO2 phase under pressure.The α-PhO2 phase remained after the decompression.F-doped anatase TiO2 nanoflower has a lower phase transformation pressure,which is similar to TiO2 bulk materials.The high pressure behavior of F-doped nanoflower is more affected by size,instead of morphology.This work provides a new method to tune the property of TiO2.(3)Phase transformation associated with luminescence from TiO2 inverse opal after calcination.An inverse opal structure of titanium dioxide was prepared and calcinated at different temperatures.X-ray near-edge absorption shows the inverse opal transforms from anatase to rutile as the temperature increases with the band gap increasing.The luminescence during the phase transformation was investigated by and X-ray excited optical luminescence.The result shows that the green emission band which belongs to the anatase phase is originated from the surface.A near-infrared emission emerges when ruitle phase starts to appear.Unlike most of the TiO2 materials so far,the inverse opal TiO2 remains as a mixed phase state for a wide temperature window.