掺杂改性型纳米二氧化钛的制备与性能表征

【作者】 刘立强；

【导师】 彭兵；

【作者基本信息】 中南大学 ， 环境工程， 2009， 硕士

【摘要】 当前纳米二氧化钛光催化剂存在的主要问题是:TiO₂光催化剂对光的吸收范围狭窄,主要集中在紫外光区,对可见光基本无光催化活性;半导体载流子复合效率高,量子效率低。为了提高TiO₂的可见光催化活性及抗菌性能,综合分析TiO₂光催化机理及改性原理,本课题提出了以廉价的硫酸氧钛为钛源,尿素为氮源,通过高温煅烧对二氧化钛进行氮掺杂改性及将氮掺杂和载银两种改性手段相结合的思路,并考察了改性对TiO₂光催化剂的抗菌性能和光催化性能的影响,得到如下结果:以廉价的TiOSO₄为原料,通过水解法制备正钛酸前驱体,然后向正钛酸前驱体中加入尿素作为氮源,经煅烧制备了氮掺杂纳米二氧化钛。考查了不同煅烧温度、Ti/N配比、煅烧时间、pH值等因素对光催化性能的影响。用X射线衍射、紫外-可见吸收光谱、热重-差热分析和X射线光电子能谱等方法对制备的样品进行了表征。结果表明:氮掺杂最佳实验条件为煅烧温度400℃、n（Ti）:n（N）=1:4、煅烧时间1h,光催化反应体系最佳pH为3。物化性能分析显示制备的样品均为锐钛型,氮掺杂使二氧化钛在可见光区（380～780nm）的光吸收明显增强,部分氮取代TiO₂晶格中的氧原子。氮掺杂后的光催化性能得到了显著提高,实验条件下15min对甲基橙的降解率达到97%,抗菌实验表明杀菌率达到90%。以载银纳米TiO₂和尿素为原料,通过高温煅烧混合物法制备了氮掺杂载银纳米TiO₂。用X射线衍射、紫外-可见吸收光谱、透射电镜和X射线光电子能谱等方法对制备的样品进行了表征。考察了煅烧温度、Ti/N配比、光照条件等因素对粉体的光催化抗菌性能的影响。结果表明:最佳制备条件为煅烧温度400℃、n（Ti）:n（N）=1:4、煅烧时间1h。物化分析表明复合粉体中氮的形态与氮掺杂纳米TiO₂基本一致。复合粉体实验条件下25min对甲基橙的降解率达到90%。粉体在暗态和光照条件下的抗菌率均达到99%,氮掺杂对载银纳米TiO₂的Ag⁺溶出基本无影响。结合实验结果,基于第一性原理,计算了TiO₂、掺氮TiO₂和氮氢共掺杂TiO₂的能带结构、态密度和光学性质。分析发现氮掺杂和氮氢共掺杂都能使TiO₂的禁带变窄,可见光吸收增强。从态密度的分析可以更加清楚的发现这些变化的原因是N或N-H掺杂取代TiO₂晶格中O引起的,进一步从理论上证实了实验结果。更多还原

【Abstract】 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.更多还原