Preparation And Optical Property Study Of Zinc Doped TiO₂Nano Film

With the development of technology and advance in social development,environmental and energy issues have become the most two important issues ofhuman society. TiO₂as a safe, non-toxic and easily obtained semiconductormaterial, has been widely used in solar energy and environment protectionbecause of its excellent performance in photocatalysis and photoelectric effect.However, there are still two major unresolved problems that impede the practicalapplication of TiO₂. one is titania’s ineffectiveness under visible light; the bandgap of anatase is3.2eV, which requires excitation wavelengths ofλ<376nm.Given that less than5%of the solar flux incident at the earth’s surfacelies in this spectral regime, harvesting sunlight for photocatalytic orphoto-electrochemical purposes would be enormously enhanced by extendingthe photo-response of TiO₂into the visible region. The other one is the generatedconduction electron and valence band hole recombination in the bulk decreasethe catalytic efficiency of TiO₂. Doping TiO₂with metal iron or composite TiO₂with another semiconductor are effective ways to solve the problems. In thispaper, TiO₂nanofilms were prepared on glass substrates by sol-gel method, theeffects of different temperatures on the degree of crystallinity and optical properties of thin films were studied. In order to utilized the visible light, TiO₂was doped with Zn2+or composited with ZnO in this paper to prepareTiO₂/ZnTiO3composite film, and the factors affecting the performance of thecomposite films were discussed. X-ray diffraction（XRD）, X-ray photoelectronspectroscopy（XPS）, UV-visible absorption spectrum（uv-vis） were used to studythe morphology, crystal structure, chemical composition and spectral responsecharacteristics of the films. The photocatalytic activities of samples wereevaluated by measuring degradation rates of the methylene blue（M.B） moleculein aqueous solution under visible light irradiation.After the heat treatment at different temperatures, the TiO₂power andfilms prepared by sol-gel method present different crystalline properties andsurface morphology. The crystalline properties increase with the increase oftreatment temperature. The highest degree of crystallinity was obtained when thesamples calcined at500℃, and grain size was more even; but when the heattemperature rise to650℃, rutile was obtained. The film calcined at differenttemperature has different absorption capacity on the UV light. When calcined at550℃, the film has the strongest absorption capacity; and there is a blue shiftwhen the film is calcined at650℃. However, all the samples show littleabsorption in the visible light. After the heat treatment at550℃, the anataseTiO₂films with better crystal properties and surface morphology show betterphotocatalytic degradation under UV light irradiation in degradation the MBsolution, after300minutes irradiation,85%M.B was degraded. When the heat treatment increase to650℃, the films are a mixture phase of anatase and rutile,and the photodegradation efficiency also decreased, reaching75%afterirradiated under UV light for300minutes.The TiO₂/ZnTiO₃composite films was prepared by adding differentproportions of ZnO powder into the TiO₂sol precursor. After calcined at550℃for2hours, different crystalline TiO₂thin films with complex perovskite ZnTiO₃phase were obtained. The TiO₂crystal form of the TiO₂/ZnTiO₃compisite filmhad a obvious influence on the absorption ability in the UV light; the absorbanceof the UV light first increase then decrease with the increase of content oftitanium zinc in the compisite films. In the TiO₂/ZnTiO₃photocatalyticcomposite film, when the ZnTiO₃phase content was low, the three-phasecomposite film which made up of anatase, rutile and perovskite showed betterphotocatalytic activity under UV light compared with the pure TiO₂, reachingabout93%under UV irradiation for300minutes.TiO₂and zinc titanate composite nano film materials was prepared bysol-gel method with zinc acetate as the source of zinc. Then composite film withdifferent TiO₂crystal type and perovskite phase ZnTiO₃were obtained by heattreatment at550℃for2hours.There is a obvious distinguish in surfacemorphology between pure TiO₂and TiO₂doping with Zn element（the Zn sourceis ZnAc）:After Doping,particles on the materials surface are more tiny, and havea reunion phenomenon. ZnO separated on the thin film surface when with highzinc doping amount;Composite strcture had not widen the light response area of the materials. But the composite structure with anatase phase TiO₂andperovskite phase ZnTiO3can improve the light carrier separation efficiency.