【作者】 李慧；

【导师】 隋卫平；

【作者基本信息】 济南大学 ， 化学工程（专业学位）， 2015， 硕士

【摘要】 二氧化钛是一种催化活性高、无毒无污染、价格低廉、性质稳定的n型半导体光催化剂,然而,TiO2存在两大方面的缺陷:一是TiO2的禁带宽度比较大,带隙能为3.2eV,也就是说二氧化钛只有在受到波长小于387.5nm的紫外灯照射时才会激发产生光生电子和空穴,但是紫外光在太阳光中所占的比例还不足5%,这使二氧化钛在日常应用中对太阳光的利用率极低;二是光生电子和空穴很不稳定且非常容易发生复合,这严重降低了二氧化钛的光催化性能。从而,减小带隙能和降低电子空穴对的复合率成为了拓宽TiO2的应用领域及改善其光催化活性的重要突破口。为了实现上述突破,必然要对TiO2进行改性研究。迄今为止,研究者已经研制出许多应用于TiO2改性的方法,其中离子掺杂和半导体复合是我们在本研究中所采用的两种改性方法,改性处理不仅将TiO2的光响应范围拓宽到可见光区域,而且大大降低了光生电子-空穴对的复合率。本论文主要研究了以下几个方面:(1)TiO2薄膜及TiO2-ZnO复合薄膜的制备及性能测试该实验选用钛酸四正丁酯和二水合醋酸锌分别作为钛源和锌源,采用溶胶-凝胶法制备出TiO2胶体和ZnO胶体,将陈化好的胶体按一定体积混合搅拌得到TiO2-ZnO复合胶体,采用浸渍提拉法在洁净干燥的玻璃基体上拉制薄膜,待薄膜干燥后,采用外掺杂的方法在其表面掺杂离子Ce、F、Ca、Fe、La,待离子溶液自然风干后,将薄膜置于马弗炉中进行高温焙烧,通过对甲醛的降解性能测试来确定离子的最佳单双掺浓度。薄膜对有机污染物降解的实验结果表明了离子掺杂复合改性之后的TiO2薄膜光催化活性得到了显著的提高。(2)TiO2及TiO2-ZnO光催化剂的表征本研究通过使用紫外-可见分光光度计(UV-vis)、荧光光谱(PL)仪、场发射扫描电镜(FE-SEM)、差热-热重分析仪(DTA-TG)、X射线衍射仪(XRD)及氮气吸附-脱附仪(BET),对薄膜和粉体进行了一系列的光学性能及结构表征。红移及荧光光谱分析结果表明了:离子掺杂和复合改性不仅诱发了薄膜较强的可见光吸收,而且降低了电子-空穴对的复合率;DTA-TG及XRD结果显示了改性后的催化剂晶型主要维持在光催化性能最好的锐钛矿;FE-SEM及BET测试揭示了复合改性的薄膜是由较小的纳米粒子构成的,同时具有较大的比表面积。(3)光催化机理的探讨首先,ZnO与TiO2复合后会形成交错能级,经光照射时,ZnO导带上的电子会很容易地被激发到TiO2的导带上,相反,TiO2价带上产生的空穴会转移到ZnO的价带上,因此ZnO复合后大大降低了TiO2的带隙能及电子-空穴的复合率。其次,半径较小的离子掺杂后会与TiO2形成掺杂能级,从而进一步减小其带隙能;半径较大的镧系金属离子掺杂后会引起TiO2的晶格扭曲,使其能够接收更多的光生空穴并产生更多的自由基来氧化吸附的有机污染物分子。另外,掺杂的离子可以结合电子或空穴,阻止其复合的进行。(4)应用领域的拓展与以往研究不同,本研究将离子掺杂后的TiO2-ZnO复合薄膜主要应用于甲醛这一新兴污染物的降解,使其在实际生活中更加具有应用价值。更多还原

【Abstract】 TiO2 as an n-type semiconductor, it is highly photocatalytic, nontoxic, inexpensive and stable. However, TiO2 has two shortcomings: one is that the width of forbidden band is larger and the band gap energy is 3.2eV, that is to say, only when TiO2 is illuminated under UV light which wavelength is smaller than 387.5nm can the photogenerated electrons and holes be produced. But the ratio of UV light in the sun is less than 5%, which leads the lower utilization of sunlight by TiO2. Two is that photogenerated electrons and holes are so unstable that they can easily recombine, which reduces the photocatalytic activity of TiO2. Therefore, to narrow band gap and to prohibit the recombination of photogenerated electrons and holes have become two important problems, in order to broaden the application area of TiO2 and improve its photocatalytic activity.The modification research of TiO2 is necessary to realize the above problems. So far, the researchers have found many methods applied in the modification of TiO2. Among all kinds of methods, ions doping and semiconductor composition are adopted in our research. The modification can not only broaden the light response range of TiO2 to visible light area, but also greatly reduce the recombination rate of electronic- hole pairs.The research of the paper mainly contains the following aspects:(1)The preparation and performance tests of TiO2 and TiO2-ZnO films.We selected Ti(C4H9O)4 and Zn(CH3COO)2.2H2 O as precursors and used sol-gel method to prepare TiO2 colloid and ZnO colloid in experiment, respectively. TiO2-ZnO composite colloid can be made by mixing TiO2 colloid and ZnO colloid in a volume ratio of 2/1. The pure TiO2 and TiO2-ZnO composite films were prepared by dip-coating process on clean and dry glass substrates. The doping ions Ce, F, Ca, Fe and La were doped on the surface of films to prepare the ion doped films. After the ion aqueous solution on surface were dry, the films were put in the furnace to burn. The best ion doping concentration was determined by the performance test of films in degradation of formaldehyde. The experiment results of degradation of organic pollutants showed that the the photocatalytic activity of TiO2-based composite films was obviously improved.(2)The characterization of TiO2 and TiO2-ZnO catalystsThe optical properties and structure of prepared catalysts were characterized by photoluminescence(PL) spectra, UV-Vis diffraction reflectance absorption spectra(DRS), X-ray diffraction(XRD), differential thermal analysis-thermogravimetry(DTA-TG), field emission scanning electron microscopy(FE-SEM), and N2 adsorption/desorption isotherms. The DRS and PL spectra results showed that multi-modification not only induced strong visible light absorption of TiO2 but also reduced the recombination rate of electron-hole pairs in the composite film. The DTA-TG and XRD results indicated that the crystal type of the TiO2 composite film is mostly stabilized in anatase. The FE-SEM and BET surface area results revealed that the small nanoparticles constituted modified TiO2 composite film with the large specific surface area.(3)The description of photocatalytic mechanismsFirstly, the presence of doping energy level in coupled materials is relevant to this behavior: the electrons on the conduction of ZnO can be easily inspired to the conduction of TiO2 under irradiation, on the contrary, the generated holes on the valence band of TiO2 transfer to the valence band of ZnO, as a result, the recombination rate of the pairs is decreased and the availability of the pairs in redox process is increased. Secondly, the doping level can be formed after doping of the ions which have smaller radius than Ti; doping lanthanide ions which have larger radius than Ti can contribute to the formation of titanium dioxide lattice distortion, which could accept more photoexcited holes and produce more surface free radicals to oxidate adsorptive molecules. In addition, the doping ions can capture electrons or holes to prevent their recombination(4)Development in the field of applicationDifferent from the before researches, the ion doped Ti O2-ZnO composite films were used in the degradation of formaldehyde which is a emerging contaminant, in this way, the actual application value of TiO2 is increased.更多还原