【作者】 过军芳；

【导师】 范杰；

【作者基本信息】 浙江大学 ， 化学， 2011， 硕士

【摘要】 光催化技术在解决能源危机和处理环境污染方面得到了广泛研究。Ti02由于其无毒无害,化学稳定性高,不会发生光腐蚀以及价格便宜储量丰富等优点而成为最有潜力的光催化剂。为了提高Ti02的光催化活性,科学家们从制备纳米二氧化钛催化剂并对其进行改性等各个方面进行研究。本论文主要根据半导体光催化的理论,利用改性的溶胶-凝胶法合成掺杂的介孔Ti02材料,研究其光催化活性。研究内容主要包括：(1)通过改变Ti源前驱体,合成不同介孔Ti02,并且考察这些材料对亚甲基蓝溶液和甲醛溶液的光降解活性。实验结果发现使用不同的Ti前驱体合成的材料在对亚甲基蓝溶液和甲醛溶液的光降解活性是不一样的。在相同的焙烧温度下,对亚甲基蓝光降解效果最好的是使用TiCl4钛源前驱体,盐酸作为pH调节剂的介孔二氧化钛；而对甲醛的光降解而言,效果最好的是使用TiCl4和钛酸四丁酯共钛源前驱体。焙烧温度对亚甲基蓝和甲醛的光降解影响也不一样,对于亚甲基蓝而言,最佳焙烧温度为450℃,对甲醛而言,最佳焙烧温度为350℃。主要是由于两个反应中影响光降解速率的因素不一样。对于亚甲基蓝的降解而言,光降解速率是由晶化程度和比表面积共同作用的结果；而对于甲醛的降解而言,比表面积的作用要更大些。不同离子掺杂对材料的光催化活性的影响是不同的,有些能提高活性,如Ag+,Bi3+；有些反而使活性降低,如Ca2+。(2)利用改性溶胶-凝胶法(AcHE法)合成含苯硅氧烷介孔Ti02材料,考察掺杂浓度对降解亚甲基蓝的光催化活性的影响。光催化结果表明,掺杂材料对降解亚甲基蓝的活性相对于纯Ti02提高了很多,最佳掺杂浓度为1%。利用XRD,BET, TG, TEM,固体NMR, EPR等方法对材料进行表征探索催化活性改变的原因。表征结果分析得出制备的样品均为锐钛矿,掺入含苯硅氧烷后材料的晶化被抑制,固体NMR结果表明在350℃焙烧后,碳硅键断裂导致Ti02孔道中存在着芳香性碳物种。活性的提高主要是由于芳香性碳物种的存在延长电子-空穴寿命。EPR测试结果表明掺杂后的材料能产生更高的羟基自由基,进而可以参与亚甲基蓝的氧化反应,这也是光生电子-空穴的复合速率减慢的结果,与荧光测试结果一致。(3)利用改性的溶胶-凝胶法(AcHE法)合成了Cu掺杂介孔TiO2,并考察它在无氧条件下分解甲醛溶液产氢的光催化活性。Cu的掺入大大地提高了催化剂的活性,同时掺杂浓度和焙烧温度对催化剂产氢能力都有影响,最佳的掺杂浓度为1%,最佳的焙烧温度为350℃。与此同时,二氧化碳也是一种生成物。比较反应过程中产生氢气和二氧化碳的物质的量之比发现,在低温焙烧下,低掺杂量(Cu%≤2%),产生的氢气和二氧化碳的物质的量之比为2：1；当增大掺杂浓度(Cu%≥5%)时,产生的氢气和二氧化碳的物质的量变为1：1。焙烧温度同样会影响到氢气和二氧化碳的比例。在低温焙烧时(≤450℃),产生的氢气和二氧化碳的物质的量之比为2：1,高焙烧温度(≥550℃)产生的氢气和二氧化碳的物质的量变为1：1。减少甲醛量到330μmol,延长反应时间,产生了500μmol的氢气,侧面证明了水参加了反应。XPS的结果表明低温焙烧时,低掺杂浓度(Cu%≤2%),Cu完全以一价存在；当增大掺杂浓度一价铜开始转变为二价铜。高温焙烧也使得一价铜转变为二价铜。一价铜的存在能使水参与分解反应,而二价铜却不能。DFT理论计算证明高浓度Cu掺杂或是高温焙烧使Cu生成一个很大的能垒,材料的带隙能过小,不能分解水。更多还原

【Abstract】 Photocatalysis has been widely studied because it has the ability to solve the energy crisis and environmental pollution. TiO2 is one of the most promising photocatalysts due to its non-toxicity, chemical stability and rich abundance. Many stategies have been developed to improve the photocatalytic activity of TiO2. In this thesis, mesoporous TiO2 was synthesized using a modified sol-gel process. Their photocatalytic activity in photodegradation of dyes and formaldelyde under UV light was investigated. In addition, the doping of aromatic carbon or Cu ions have been proved to be an efficient way to improve their photocatalytic performance. This dissertation consists of the following contents.(1) Mesoporous TiO2 was synthesized with different Ti precursor. The photoactivity on methylene blue degradation and formaldehyde decomposition over these samples were investigated. For the two typical reactions, it was found that the photocatalytic procedures were not the same. On photodegradation of methylene blue, the photocatalyst using TiCl4 as Ti precursor and hydrochloric acid as pH regulators showed the best activity. However, formaldehyde decomposition proceeded much faster over samples using TiCl4 and tetra butyl titanate ester as co-titanium precursor. The effect of calcinations temperature on photocatalytic efficiency of methylene blue degradation and formaldehyde decomposition was also different. The best temperature for TiO2 was 450℃in the case of methylene blue degradation but 350℃for formaldehyde. It is concluded that the main factor influences the decomposition rate was different. As for methylene blue, it was the cooperation of crystallization and specific surface area. As for formaldehyde, specific surface area played the main role. Additionally, the influence of different ion doping was different. Some metal ions, such as Ag+, Bi3+may enhance the photocatalytic activity, while others, such as Ga2+may decrease the activity.(2) Benzene siloxane doped mesoporous TiO2 (denote as BS-TiO2) was synthesized using a modified sol-gel process (AcHE method).The influence of doping concentration was investigated. Photocatalytic tests on the photodegradation of methylene blue showed that the activity of BS-TiO2 was greatly improved compared to pure TiO2. The best doping concentration was 1%.The prepared samples were characterized with XRD, TEM, BET, TG, solid NMR and EPR. The results showed that all catalysts were anatase. The crystallization was inhibited due to the incorporation of benzene siloxane, which made better sustain mesoporous structure and specific surface area. Solid NMR results show that the bond of carbon and silicon was broken when calcined at 350℃and aromatic carbon speices exist in the pore of TiO2 which is consistent with the result of TG. The reasons of the improved activity were due to longer electronic-hole life because of the existing of aromatic carbon speices. EPR proved that more hydroxyl radicals were produced for BS-TiO2 as the result of slowed recombination rate of photoinduced electron and hole. The PL also showed that the recombination of photoinduced electron and hole was inhibited after doping.(3) Cu doped mesoporous TiO2 was synthesized using AcHE method. Its photoactivity of hydrogen generation from formaldehyde solution under anaerobic conditions was investigated. The results showed that the activity of mesoporous TiO2 was greatly improved with the best doping concentration of 1%and the best calcination temperature of 350℃. Meanwhile, the carbon dioxide was also evolved as the by-product. It was found that the molar ratio of the amount of hydrogen and carbon dioxide was 2:1 with low doping concentration Cu%≤2%) and changed to 1:1 with increased doping concentration (Cu%≥5%). In addition, elevating calcination temperature led to the similar trend. When the amount of formaldehyde was reduced to 330μmol,500μmol hydrogen were produced, which proved that water must participat in the photocatalytic reaction. the XPS results showed that Cu(I) was extensively exsited with low doping concentration Cu%≤2%) and began to convert into Cu(Ⅱ) with increasing the doping concentration (Cu%≥5%). In addition, high calcination temperature also led to the formation of Cu (Ⅱ). We have shown that Cu(Ⅰ) favors the H abstraction from water but Cu (Ⅱ) doesn’t. DFT theoretical calculations proved that high doping concentration or high calcinations temperature make the band gap of catalyst too small to decompose water.更多还原