Sol-gel Synthesis And Study Of Ag, V-doped TiO₂Powders

Nano-TiO2have many excellent properties, such as a unique semiconductor, gas sensing, photosensitive, photocatalysis. For this reason, it is widely applied to photocatalysis, dye-sensitized solar cells, sensors, self-cleaning ceramic, antimicrobial self-cleaning glass etc. In recent years, people begin to pay attention to the preparation and study of doped nano TiO2in order to improve its performance and get more extensive application.Nano TiO2powders were syethezied by sol-gel method in this paper. V-doped and Ag-doped TiO2powders were also prepared by sol-gel method. Crystalline structures, grain size, crystalline transitions and photoluminescence properties of as-prepared TiO2powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analyzer-thermogravimetric analysis (DSC-TGA) and photoluminescence analyzer (PL). Grain sizes of TiO2nanograin and the relative contents of TiO2allotropic crystals were calculated by Scherrer formula, Spurr-Myers method, respectively. Growth activation energys for TiO2nanocrystals were calculated based on growth kinetics equation. The mechanism of the formation of TiO2nano crystals is discussed.The results show the grain sizes of TiO2nanograins in13~60nm. With the increase in calcined temperature, the crystal structure of TiO2changed from amorphous to anatase to rutile. An orientation relationship of anatase (112)//rutile (100) with coherent phase boundary has been observed first. Calculation result shows that the activation energys for the grain growthes of anatase and rutile phases are in the range of30~40kJ mol-1and8kJ mol-1, respectively. There are6peaks on photoluminescence spectra of TiO2powders. Among them,396nm and419nm peaks are responsible for the near band edge emissions of anatase and rutile phases. The other4pealks of449nm,466nm,481nm and490nm are responsible for various defects in TiO2grains.Compared with undoped TiO2powders, the temperature range of stable anatase for Ag-doped TiO2is wider. A mixture of amorphous and anatase appears in low temperature of100℃and anatase can keep up to the temperature of600℃. Compared with undoped TiO2powders, the temperature range for transiting anatase to rutile of Ag-doped TiO2powders is narrow. Ag doping inhibited the growth of TiO2grains. The nucleation and growth of Ag crystals on TiO2grain boundaried can be observed by TEM. Compared with undoped TiO2powders, a new exothermic peak for a decomposition of AgNO3at380℃occurs and the exothermic peak of organic oxidation shifts to of60~70℃to high temperature on DSC-TGA curves of Ag-doped TiO2powders. PL spectra of Ag-doped TiO2powders show that amount of Ag doping increases PL intensity, and results in the emergence of the peak for the near band edge emissions of anatase phase and the peaks for oxygen vacancies on crystal surface.Compared with undoped TiO2powders, V doping can enhance the transformataion from anatase to rutile at600℃but there is the opposite effect at700℃, which indicates that the V doping may have abnormal phenomenon in the crystal transformation from anatase to rutile.