【作者】 马云飞；

【导师】 张金龙；

【作者基本信息】 华东理工大学 ， 先进材料与制备技术， 2012， 博士

【摘要】 随着人口数量的增加和经济的快速发展,资源成为全球日益关注的问题,尤其是能源和水成为人类社会发展所不可短缺的二大资源。半导体二氧化钛除了可用于光解水制氢作为获得能源的一种方法外,其在高级氧化技术方面也被广泛用于污染物降解,净化水质和空气等。但是,TiO2的禁带宽度较大,只有当波长小于387 nm的紫外光激发时,才能产生电子和空穴,并且光生载流子极易复合。因此开发具有可见光响应的二氧化钛光催化剂是当前光催化领域研究的重要任务。针对以上二氧化钛在实际应用中存在的问题,本论文通过共掺杂的方法对二氧化钛进行改性研究以提高其在可见光区域的光催化活性,主要工作分为以下五个部分。1.采用硫酸钛为钛源,氨水作为沉淀剂的同时作为氮源,制备了钐、氮共掺杂的纳米TiO2光催化剂。通过XRD、TEM、XPS BET、FTIR等方法对催化剂进行了表征,并在可见光下考察了催化剂对水杨酸的降解率。UV-vis表征结果表明N-TiO2在可见光区域有很好的吸收,XPS结果表明N物种以间隙掺杂的形式存在,形成了Ti-O-N键和O-Ti-N键。钐的掺杂可以控制晶粒的增长,同时又可以抑制晶相的转变,并且钐的加入促进了催化剂对目标污染物的吸附,有利于光生载流子快速向目标污染物转移,所以Sm/N-TiO2显示出比纯TiO2和N-TiO2更高的光催化活性。在本研究中,1.5Sm/N-TiO2在400℃下煅烧2h后显示出最高的光催化活性。这归因于催化剂对可见光的良好吸收,合适的晶粒大小和高的比表面积,对目标污染物的良好的预吸附以及电子和空穴的有效分离。2.采用沉淀-胶溶法制备了铕、氮共掺杂的TiO2光催化剂。通过XRD、XPS、UV-vis、TEM等表征方法对Eu/N-TiO2进行表征。样品以锐钛矿为主,同时有少量板钛矿相存在。由于氮和铕的协同作用,改性催化剂的可见光活性得到了很大程度的提高。当铕的含量达到1%时,催化活性最高,在可见光下照射5h后,对50 mg/L的水杨酸溶液的降解率达到88%。等温吸附实验证明铕的掺杂大大提高了吸附速率常数以及最大吸附量,铕是催化剂的吸附活性位点,同时由于铕的价电子可变性,其也是光生电子的浅势捕获陷阱,从而有效地抑制了电子和空穴的复合。通过加入不同的探针分子证明在本催化反应过程中,首先是水杨酸吸附在催化剂表面,然后在可见光的照射下产生光生电子和空穴,空穴进一步产生羟基自由基,与表面吸附的水杨酸反应。3.采用原位酯化法,以三乙醇胺为氮源,制备了铽、氮共掺杂的二氧化钛光催化剂。以20 mg/L的二号橙作为目标污染物,对所制得的催化剂在可见光下的催化活性进行了评价。在制备过程中,以少量的浓硫酸作为酯化反应催化剂,大大增加了催化剂表面的酸性,提高了催化剂对目标污染物的吸附,有利于AO7的降解。氮的掺杂拓展了催化剂在可见光区域的吸收,铽的加入有效地控制了晶粒的大小,在铽的掺杂量为1.0%时,其对AO7的降解率最高,5 h内其脱色率为100%。并且在可见光作用10 h后,AO7的萘环和苯环全部被开环降解。4.采用二次水解法在没有模板剂的条件下以硫酸钛为钛源,先制备了具有介孔结构的二氧化钛,然后通过浸渍煅烧法得到了钐掺杂的二氧化钛,最后在一定浓度的葡萄糖溶液中180℃水热处理后250℃煅烧2h,得到了钐、碳共掺杂的二氧化钛。采用XRD,TEM, UV- vis, XPS, N2吸附-脱附和Raman等方法对样品进行了表征。以20 mg/L的苯酚为目标降解物,当钐的浸渍量为0.5%时,其光催化活性最高,5h内对苯酚的降解率达到95%。钐的加入抑制了二氧化钛纳米粒子的烧结,保证了较小且均匀的晶粒尺寸,碳以间隙和取代掺杂的形式进入了TiO2的晶格,在二氧化钛的能带结构中形成了新的掺杂能级,降低了禁带宽度,促进了对可见光的利用,增加了光生电子和空穴的产率。Sm和C的协同作用大大提高了催化剂的可见光活性。5.采用蒸发自组装法以钛酸四丁酯为钛源,正丁醇为溶剂,三聚氰胺为氮源,制备得到了不同镱含量的Yb,N共掺杂的有序介孔TiO2。采用XRD, TEM, UV- vis, XPS和N2吸附-脱附等方法对样品进行了表征。经350℃煅烧处理后,掺杂量为3%的Yb,N共掺杂的二氧化钛具有最高的比表面积(219 m2g-1),同时具有有序的二维六方相的介孔结构。光催化活性显示经10h的可见光照射后,3.0Yb/N-TiO2对20 mg/L的苯酚溶液的降解率为75%,而经4 h可见光照射后,10 mg/L罗丹明B溶液可被该催化剂彻底矿化。氮的掺杂有效地拓展了其在可见光区域的吸收,而镱的掺杂一方面稳定了其介孔结构,另一方面又有效地抑制了电子和空穴的复合,延长了光生载流子的寿命。更多还原

【Abstract】 With the increase in human population, resources are becoming the problem concerned to all the people. Water and energy are the two indispensable resources of the development of human society. As a type of semiconductor photocatalyst, TiO2 can be used in hydrogen production by photosplitting of water, which is a new method to produce energy. Because of the advantages of non-toxic and low cost, TiO2 can be used for water treatment and air purification by advanced oxidization process. But the problem with TiO2 is that, because of wide band gap, TiO2 can only be excited by the UV light of wavelength below 387 nm, and the photogenerated electrons and holes are easy to recombine. So it is important to synthesize high efficient visible-light-responsive TiO2 for the photocatalytic reaction.In order to counter the problems of TiO2 for the practical application, co-doping is used in the present research to modify TiO2 which enhances its photoactivity in visible light region of solar spectrum. The main work is composed of five parts:1. TiO2 co-doped with samarium and nitrogen was synthesized by co-precipitation method with titanium sulfate as titanium precursor and ammonium hydroxide as precipitating agent and nitrogen precursor. The samples were characterized by XRD, TEM, XPS, BET and FTIR. The photocatalytic activities of the samples were evaluated by degradation of salicylic acid under visible light irradiation. UV-Vis spectra showed that N-TiO2 had strong absorption in the visible light region. XPS results showed that nitrogen was incorporated into TiO2 matrix in the form of interstitial doping model existing in the bond of Ti-O-N and O-Ti-N. The doping of samarium inhibited the growth of crystallite size and the transformation from anatase to rutile phase. Meanwhile, the addition of samarium was beneficial for the adsorption of the target contaminant and the transfer of the photogenerated carriers. Therefore, Sm/N-TiO2 presented much higher photocatalytic activity than N-TiO2 and pure TiO2 under visible light irradiation. In our research work, the optimal dosage of samarium was 1.5% for the highest photocatalytic degradation and the sample calcined at 400℃showed the best photoactivity. This could be explained by better absorption in visible region, the appropriate crystallite size, high surface area, stronger pre-adsorption of target contaminant and more efficient separation of electrons and holes.2. TiO2 co-doped with europium and nitrogen was synthesized by precipitation and peptization method and characterized by XRD, XPS, UV-vis spectra and TEM. The results showed the samples were composed mainly of anatase with a little brookite. The great enhancement in photocatalytic activity was attributed to the synergistic effect of nitrogen and europium.1.0Eu/N-TiO2 showed the highest activity and 88% salicylic acid was degraded after 5 h visible light irradiation. The adsorption isotherms illustrated that europium doping was beneficial for the adsorption of salicylic acid and increased the adsorption rate constant and maximum adsorption amount. Meanwhile, for the varied valence, Eu is the shallow trap of electrons and suppresses the recombination of electrons and holes efficiently. The probable degradation mechanism of salicylic acid was investigated by the addition of NaF, Na2S2O3 and K2S2O8. It was verified that salicylic acid was first adsorbed on the surface of the catalysts, followed by the degradation from the hydroxyl radicals generated by the holes (hvb+).3. Terbium and nitrogen co-doped TiO2 was synthesized by in situ esterification and trolamine was used as the nitrogen precursor. The photocatalytic activity was evaluated by the degradation of 20 mg/L AO7. The usage of sulphuric acid as the catalyst for esterification increased the acidity of the surface of the catalyst which enhanced the adsorption of the contaminat. The doping of Nitrogen extended the absorption range to the visible region. The addition of Tb restrained the growth of the crystallite and further enhanced the adsorption of the contaminant. When the dosage of Tb was 1%,1.OTb/N-TiO2 showed the highest photocatalytic activity. After 5 h irradiation under visible light,100% AO7 was decolorized. After 10 h irradiation, the ring of benzene and naphthalin was degraded.4. Mesoporous TiO2 was synthesized by hydrolysis of titanium sulfate for two times free of template. Sm was loaded on the mesoporous TiO2 by impregation in the solution containing certain amount of Sm(NO3)3. Then the samples were hydrothermally treated at 180℃in glucose solution. Sm, C co-doped TiO2 was obtained after washing, filtering and calcined at 250℃for 2 h.0.5Sm/C-TiO2 showed the highest activity under the irradiation of visible light. After 5 h irradiation, the degradation of 20 mg/L phenol is about 95%. The addition of samarium restrained the coaggregation of the TiO2 nanoparticles and ensured the small and homogeneous crystallite size. Carbon is incorporated into TiO2 matrix in the form of interstitial and substitutional and new band was formed in the band of TiO2. The synergistic effects of samarium and carbon enhanced the absorption of visible light, improved the separation of photogenerated holes and electrons and thus increased the visible light photocatalytic activity obviously.5. Well-ordered mesoporous TiO2 co-doped with nitrogen and ytterbium was successfully synthesized by an evaporation-induced self-assembly (EISA) method. TBOT was used as the titanium precursor, n-Butanol was used as solvent and melainine was used as nitrogen precursor. The as-prepared and calcined mesoporous TiO2 materials were characterized by XRD, TEM, UV-vis absorbance spectroscopy, XPS and N2 adsorption/desorption measurements. After calcination at 350℃, the 3.0Yb/N-TiO2 had the highest surface area (219 m2g-1) and retained 2D hexagonal ordered mesoporous structures. In the presence of 3.0Yb/N-TiO2,75% of 20 mg/L phenol solution was degraded after 10 h visible light irradiation and 10 mg/L rhodamine B (RhB) was degraded completely after 4 h. The significant enhancement in the photocatalytic activity of the 3.0Yb/N-TiO2 is attributed to the synergistic effect of N and Yb. The N dopant extended the absorption to the visible region and the Yb dopant was beneficial for stabilizing the mesoporous structure and restraining the recombination of photogenerated holes and electrons.更多还原