The Modification Of Metal Ion Doped Titanium Dioxide Photocatalysts

To solve the application technique problems of low utilization efficiency of solar energy and photon quanta for TiO₂ catalyst, people have done some studies to improve the performance of TiO₂ by doping metal elements. Doping metal could induce defects on the surface of TiO₂, change the crystallinity, affect the reuniting of electrons and holes or broaden the photon-excited wavelength, hence change the photocatalytic activity of TiO₂. But most studies aim at the doping of very few elements and there is no comprehensive comparison of the performances doping with different elements by now. There are few researches on how to broaden absorption spectra in doping system and opinions vary about mechanism of improving performance.In this thesis, TiO₂ powders and TiO₂ films doped with transitional metal ions and noble metal elements were prepared by sol-gel method, and characterized by various techniques, such as UV-Vis absorption spectra (UV-Vis), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM), BET surface area and so on. It was the first time that the changing laws of crystal type, Grain fineness number, BET surface area, unit cell parameter, absorption spectra and catalytic activities for nanometer TiO₂ catalysts doped with fourteen elements in the same conditions were studied from every side. The doped elements are V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pt, Au, Rh, Pd, Ag and Ru respectively.The particles of the powder prepared in this experiment were round shape with good dispersity and small size. When calcined at 773 K, the TiO₂ in composite catalysts exesits as anatase structure and its grain fineness number was between 10 and 25 nanometers. Their BET surface areas were between 30.4 and 77.1m²/g, much larger than commercial TiO₂ powder. The BET surface areas of TiO₂ powder increased after doped with nickel, iron and manganese and decreased evidently when doped with rhodium accompanying with particles aggregating phenomenon.In the studies of light absorption performance, the photon excited wavelength of TiO₂ powder were broaden to visible light markedly for the first time when doped with most transitional metal and noble metal elements except zinc and silver elements. The red shift had exceeded the report of documents. Broader absorption spectra are propitious to the application of TiO₂ photocatalyst under visible light.In photocatalytic reaction, three kinds of light source were adopted, one was high pressure xenon lamp to simulate sunlight, one was the spectrum of high pressure xenon lamp whose most ultraviolet radiation were filtered by water, glass and FeCl₃ solution, and another was light of 465 nm wavelength.Under the irradiation of simulant sunlight, the effect of calcination temperature on photocatalytic activity was studied. The photocatalytic activities of pure TiO₂ powder calcined between 673K and 873K were better. At the same time, the effect of doping elements on photocatalytic activity of TiO₂ powder calcined at 773K was studied too. Results showed that the photocatalytic activity of TiO₂ powder enhanced when doped with zinc, platinum, gold or palladium, while decreased obviously when doped with manganese, chromium or silver.When irradiated with visible light by the latter two kinds light source, the photocatalytic degradation of methyl orange showed that after doped with iron, platinum, vanadium, copper or palladium TiO₂ powders had visible light photocatalytic activity. Among them, photocatalytic activity Fe/TiO₂ powder and Pt/TiO₂ powder were better. Although most doping elements broaden the absorption spectra of TiO₂, not all of them enhanced the photocatalytic activity. This indicates that light absorption performance is not the only factor to determine the photocatalytic activity.Powder is difficult to separate and reclaim, so the TiO₂ film as well as gold and zinc doped TiO₂ films were prepared by using a sol-gel method on glass sheet. The surface of films was smooth, compact and firm, without rift. The films were very thin and the crystal sizes belonging to nanometer scale. The calcination temperature and loaded layer number can affect the photocatalytic activity of films. The photocatalytic activity is better when the films cacined at 673K and 773K and that enhances gradually with the increasing of coating cycles. In addition, doping elements have great influence on the photocatalytic activity of films. The photocatalytic activity of TiO₂ films were improved after doped with gold element, while decreased after doped with rhodium element.Pt/TiO₂ powder was used as photocatalytic catalyst to degrade p-nitrophenol, RDX and TNT in this thesis. Under the irradiation of simulant sunlight, their photocatalytic degradation reactions follow first order kinetics. When irradiated for 4hs, their conversion rates got up to more than 90%.The photon excited wavelength of TiO₂ photocatalyst was broaden and the weakness of being unable to utilizate visible light was solved in the studies on improving the performances of TiO₂ photocatalyst by doping metal elements the in this thesis. The preparation method and various performances of modified TiO₂ photocatalyst were obtained and the laws affecting the photocatalytic activity of TiO₂ were got through systematically experimental study and various data analysis.