Preparation And Characterization Of Doped Nano-modified Titanium Dioxide

The main disadvantages of nano-TiO₂ photocatalyst are as follows: the wave band for light absorption mostly locates in the range of ultraviolet (UV) radiation, while it is out of work in the visible light region; Moreover, recombining rate of electron and hole in the semiconductor is high and quantum efficiency is low. In order to enhance the photocatalytic efficiency and antibacterial performance, and analyse the mechanism of photocatalyst and modification of nano-TiO₂ synthetically, in this paper, with TiOSO₄ and urea as the raw materials, N-doped TiO₂ and N-doped Ag-TiO₂ were prepared. The photocatalytic activity and antibacterial performance were investigated. The results are as follows:TiO₂ precursor was prepared by hydrolysis of industrial titanic solution, and then urea was added as the source of nitrogen. The mixture was calcined to obtain N-doped TiO₂. The effects of calcination temperature, the ratio of N/Ti, calcination time and pH of photocatalytic reaction on photocatalytic efficiency were investigated. The prepared samples were characterized with XRD, UV-Vis absorption spectra, TG-DTA, and X-ray photoelectron spectroscopy. The results showed that the optimum prepared condition of calcination temperature was 400℃, the calcination time was 1 hour, the ratio of N/Ti was 4, and pH of photocatalytic reaction was 3. The analysis showed that: all catalysts were anatase, and the doping of nitrogen led to obvious increase in optical absorption intensity in the visible light region (380-780nm) and part of nitrogen replaced the oxygen atom in the TiO₂. The N-doped TiO₂ had high visible light photoctalytic activity and the ratio of degradation of methyl orange could reach 97% in 15 min under experiment condition; antibacterial rate can reach 90%.N-doped Ag-TiO₂ was prepared by calcination of mixture of Ag-TiO₂ and urea. The prepared samples were characterized using XRD, UV-Vis absorption spectra, TEM and X-ray photoelectron spectroscopy. The effects of calcination temperature, the ratio of N/Ti and calcination time on photocatalytic efficiency and antibacterial performance were investigated. The results showed that the optimum prepared condition of calcination temperature was 400℃, the calcination time was 1 hour, and the ratio of N/Ti was 4. The analysis showed that the character of N in the N-doped Ag-TiO₂ was the same as the N-doped TiO₂. The N-doped Ag-TiO₂ had high visible light photoctalytic activity and the degradation rate of methyl orange could reach 90% in 25 min under experiment condition; the antibacterial rate could reach 99% under the condition of illumination and darkness. The nitrogen doping had no effection on the stripping of Ag⁺ in the Ag-TiO₂.Based on experimental results and the first principles, the band structures, density of states and optical properties of the bare, N-doped and N-H co-doped TiO₂ were calculated respectively. Further analysis showed both N-doped and N-H co-doped could narrow the band gap, and extend the absorption edge of TiO₂. It could be seen from the DOS spectra that all these change was led by N and N-H atom repalaced the O atom in the TiO₂ crystal. This theory can further testify the results of experiment.