Properties Of Rare Earth Doped Titanium Dioxide Thin Films

Environment and energy are focused by people in recent years. TiO2is a wide band gap semiconductor functional materials, because there are some advantages, such as sensitive to light, non-toxic, good hydrophilic, etc, so it will have an attractive prospect in the future, it is often used in the photocatalytic self-cleaning, anti-fog glass, etc. However, TiO2can only be excited in the UV region, the utilization of solar energy is low (8percent), a lot of works have been done to improve the performance of TiO2.In this study, the single and the composite rare earth doped TiO2thin films are prepared by dip coating method. The structure, photocatalytic properties and hydrophilic properties of thin film are characterized by X-ray diffraction(XRD), UV-visible spectrophotometer(UV-VIS), Fourier transform infrared(FTIR), optical contact angle tester, respectively. It was concluded that:(1) Lanthanum doped TiO2thin films were prepared by dip coating method. The results found that the dope of lanthanum can inhibit the transformation of TiO2from anatase to rutile, but there is not obvious red shift of the response boundary of light, when TiO2thin films were prepared at550℃, the mainly crystalline phase was the anatase in the sample, and the films have the best photocatalytic performance. When0.3%Lanthanum was doped in TiO2thin films, there were more effective defects and electron capture center which can reduce the recombination rate of the hole-electron. The better catalytic performance was shown in the photocatalytic experiment of methylene blue. Because the dope of lanthanum can reduce the electronic diffusion process, the photocatalytic performance of coating layer will be decrease with the increase of the thickness. It is in accord with our experiments that one layer is better than the three layers in photocatalytic performance.The absorbing boundary of neodymium doped TiO2thin films have a red shift, so the optical absorption intensity increases. Because the dope of neodymium can significantly inhibit the transformation of TiO2from anatase to rutile, the anatase content increased when TiO2thin films were prepared at600℃. The dope of0.1% neodymium produce more capture center in the sample which can inhibit the recombinations of hole-electron pairs. As the result of it, TiO2thin film catalytic performance was improved significantly.The hydroxyl content increased in the TiO2thin films when yttrium was doped in the films, and only the anatase phase is existed, the (101) crystalline surface of TiO2was preferentially formed. The absorbing boundary of TiO2thin film has a weak red shift, thus the optical absorption intensity increases. and the dope of yttrium can reduce the transition temperature of TiC>2from anatase to rutile, so the yttrium-doped TiO2thin films prepared at a lower temperature (500℃) have a good catalytic performance. In addition, electrons have different diffusion process when different rare earth elements were doped, two layers of TiO2hin films have the highest catalytic activity in this case.(2) There are not significant change in the phase compositions of TiO2thin films when rare earth lanthanum and neodymium, lanthanum and yttrium were co-doped, respectively. The rare earth elements exist in the form of oxides, there is an blue shift of film absorbing boundary when lanthanum and neodymium co-doped in the films, so the optical absorption intensity decreased. There is not obvious blue shift of film absorbing boundary when lanthanum and yttrium co-doped in the films, but the thin films absorbance intensity decreased, the photocatalytic performance of co-doped TiO2thin films were lower than pure TiO2thin films when temperatures is below700℃.(3) The results of the hydrophilic properties are that:the hole-electron recombination rate decreased when the appropriate amount of the single rare earth (La, Nd, Y) was doped, the more hole-electrons of TiO2thin films were produced by the UV excitation, the more oxygen vacancies were formed on the surface of TiO2particles, thus the wetting properties of TiO2films improve effectively, and hydrophilic become better. In addition, with the increasing of ambient temperature, the rate of the liquid-solid interfacial tension may reduce slowly, which makes the hydrophilic properties of the films to deteriorate. The hydrophilic properties of rare earth (La/Nd, La/Y) co-doped TiO2thin films were also studied, the result is that the hydrophilic properties increase with the increase of the calcination temperature of the films.The results of photocatalytic kinetics were shown that the photocatalytic process of TiO2thin films is in accordance with the first order reaction kinetics, photocatalytic fitting kinetic constants k becomes larger when the advisable amount of single rare earth elements (La, Nd, Y) doped in TiO2thin films. The fitting kinetic constants k become smaller when lanthanum and neodymium, lanthanum and yttrium are co-doped in the films. It is consistent with the results of photocatalytic properties of the single rare earth elements (La, Nd, Y) doped and co-doped TiO2thin films, respectively.