| With the rapid development of economy and the sharp increase of the world’s population, environment pollution and energy shortage have become two urgent problems to be solved. Titanium dioxide (TiO2), a kind of semiconductor functional material, possesses the advantages of good photocatalytic activity, safety and non-toxicity and environmental friendly, and thus has wide application prospect in curbing environmental pollution and exploiting and utilizing solar energy. However, there exist two drawbacks:one is the low utilization rate of sunlight as a result of large energy gap; the other is low quantum efficiency resulting from the high recombination of photoinduced electron and hole pairs. The doping modification of TiO2is an efficient way to solve the above problems and thus improve the photocatalytic activity. In this paper, pure TiO2films were prepared on glass substrate by sol-gel method, the modification was done through doping Ag and Ag/N co-doping, and the parameters and constraints which could influence the photocatalytic activity of TiO2have been discussed. The phase composition, microstructure and optical absorption property were characterized by XRD, SEM, EDS and UV-vis. In addition, the photocatalytic activity of film photocatalyst under visible light was investigated with the methylene blue solution as a target pollutant. The main research results are as follows:For pure TiO2film photocatalyst, TiO2gradually transforms from amorphous to anatase-TiO2with increasing heat treatment temperature from300℃to500℃in the process of preparation. The crystal grains of film present the trend of growing out of nothing and expanding from small to large, and the crystalline degree increases gradually. However, when the temperature rises up to600℃, anatase-TiO2starts to transform into rutile-TiO2. The size of crystal grains becomes too large and aggregation appears. The experiment proves that pure TiO2film photocatalyst calcined at500℃is entirely made up of anatase-TiO2. The particle size is uniform, the crystalline degree is good and the average grain size is about50nm. It can absorb ultraviolet light whose wavelength is shorter than387nm but can not prominently absorb visible light whose wavelength is between387nm and800nm. The photocatalytic activity of TiO2film under visible light is very low. After illumination for300min, there occurs almost no degradation of the methylene blue solution.The modification of TiO2film was conducted by doping Ag. The results show that Ag doping can promote the transformation from anatase-TiO2to rutile-TiO2. The particle size of Ag-TiO2film (30nm) is smaller than that of pure TiO2film (50nm), and thus the corresponding surface area of Ag-TiO2film is larger than that of pure TiO2film. After the doping of Ag, the intrinsic absorption edge of film appears red-shift and the absorbance range extends to visible region. The photocatalytic activity of Ag-TiO2film under visible light is higher than that of pure TiO2film. After illumination for300min, the degradation rate of methylene blue solution is45%. The increased photocatalytic activity can be attributed to the formation of Schottky barrier on the interface between Ag and TiO2after doping Ag, which can facilitate the capture of electron, inhibit the recombination of photogenerated electron-hole and increase the quantum efficiency. Appropriate heat treatment temperature and the amount of Ag are the key factors in the preparation of high-performance film. For Ag-TiO2film, the optimum heat treatment temperature is400℃and the optimum amount of Ag is0.1wt.%under the experimental conditions.In this paper, TiO2film co-doped with Ag and N was also studied. The crystalline degree of (Ag,N)-TiO2film is fine and TiO2exits in the form of anatase. The surface of the film is composed of regular-shaped spherical particles. The average grain size is about20nm which is smaller than that of Ag-TiO2film and pure TiO2film. Meanwhile, the connection between the film and glass substrate is tight and no gaps appear between them. The thickness of the film is about150nm. Not only does the absorbance range extend to visible region, but also the absorbance intensity of visible light for the film is relatively high. The photocatalytic test proves that the photocatalytic activity of (Ag,N)-TiO2film under visible light is higher than that of single Ag-doped film, single N-doped film and pure TiO2film. After illumination for300min, the degradation rate of methylene blue solution is close to70%. The reason is that noble metal Ag can reduce the recombination of photogenerated electron-hole and nonmetal N can broaden the light absorbance range effectively. Under the combined effect of them, the photocatalytic activity of the film improves greatly. |
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