新型TiO₂的合成及光催化性能的研究

【作者】 卞振锋；

【导师】 李和兴；

【作者基本信息】 上海师范大学 ， 物理化学， 2007， 硕士

【摘要】 近年来,利用半导体光催化剂处理环境污染物已引起世界关注。TiO2以其无毒、催化活性高、化学稳定性好、价廉易得及可直接利用太阳光等优点受到人们的重视。有序介孔TiO2材料作为光催化剂用于环境污染物的处理是研究的热点之一。一方面,介孔TiO2的高比表面积提高了与有机分子接触几率,介孔孔道的存在使多相催化反应中的底物、产物有较快的扩散速度;另一方面,表面富含羟基,吸附的水能力增强,水和羟基可与TiO2表面的空穴反应产生羟基自由基,而羟基自由基是降解有机物的强氧化剂,从而有利于提高TiO2的光催化效率。然而不足之处是介孔TiO2在晶化过程中有序介孔结构会有较大的破坏,TiO2只能被波长小于380 nm的紫外光激发,光利用率低。针对目前介孔TiO2光催化领域存在的这些问题,本文通过掺杂对介孔TiO2进行了改性,发现掺杂对介孔TiO2的热稳定型,光催化活性以及在可见光下的光催化效率具有显著的提高;同时本文还采用醇解结合非表面活性剂自组装法制备了形貌新颖、具有高光催化活性的光催化剂。以苯酚,亚甲基蓝,重铬酸钾的光催化降解作为探针反应,研究了它们的光催化活性。同时采用XRD、TEM、SEM、FT-IR、XPS、RAMAN、UV、荧光光谱、氮吸附等表征手段对所制备催化剂的结构进行了表征,讨论了催化剂结构和光催化活性的关系。为进一步发展实用性光催化技术积累经验。本论文具体内容分以下四部分:一、有序介孔结构TiO2光催化剂的制备及其光催化活性研究采用溶剂挥发诱导自组装法(EISA),通过原位添加金属离子制备了一系列有序介孔结构的TiO2光催化剂。有序的介孔结构对光催化活性有促进作用,主要体现在高的比表面积和对降解物吸收能力的增强,有利于反应物在催化剂孔道中的转移。同时掺杂金属元素的研究结果表明:(1)添加一定含量的稀土La3+不仅可以有效抑制TiO2晶相的转变,稳定其介孔结构,大大地提高催化剂的热稳定型和结晶度,而且可以提高催化剂的光催化活性,从而得到具有高稳定性、高结晶度、高催化活性的介孔TiO2光催化剂;(2)添加贵金属Au可以合成介孔Au/TiO2复合物,TiO2和Au都具有很好的结晶度,同时纳米Au颗粒镶嵌在介孔的墙壁结构中。纳米Au在催化剂微结构作为电子接收器,光激发的电子和空穴由于纳米Au的存在更加有效的分离,可以有效地提高催化剂的量子效率以及光催化活性;(3)添加金属Bi3+可以合成介孔Bi/TiO2复合物,介孔结构使催化剂具有很大的比表面积,Bi均匀的和TiO2复合。Bi的掺杂使得TiO2的能带隙显著降低,从3.2 eV下降到2.7 eV,有效地提高了TiO2在可见区的吸收,催化剂的可见光光催化能力明显提高。二、醇解法制备核壳结构TiO2光催化剂及其光催化活性的研究采用无模板技术快速合成结构可调的、具有结构均一和丰富的表面结构等特点的核壳型TiO2。通过对成核的控制,得到了在水溶液中具有良好分散性和稳定性的TiO2核壳微米球。采用时间控制的手段能够在一次性生长过程中得到可控核壳结构TiO2材料。通过对核壳形成时间的调控,成功地实现了材料从核壳到空壳的转变。同时研究结果表明结构对催化剂的可见光活性也具有很大的影响,核壳结构的催化剂在相同的结晶度的条件下活性最佳。这是由于光可以在核壳结构的间隙中进行有效的漫反射,光的利用效率大大提高。这为设计高活性的催化剂做了良好的前期探索。更多还原

【Abstract】 In recent years, much attention has been paid for heterogeneous photocatalysis owing to its potential application in many areas, especially the treatment of environmental pollutants. Among semiconductor photocatalysts, TiO2 is most frequently employed because of its non-toxity, low cost, high activity and strong stability in aqueous media. Mesoporous TiO2 as photocatalyst to deal with the environmental pollutants is one of the investigative hotspot. First, high surface area of mesoporous TiO2 improves the touch probability between pollutants and catalysts, and mesopores make the products and reactants have higher diffuse rate in the multiphase catalysis reaction; On the other hand, rich hydroxyl on the surface can enhance the ability of TiO2 to adsorb water. The hydroxyl and water can yield hydroxyl free radical which react with positive hole and hydroxyl free radical is the powerful oxidant and increase the photocatalyst efficiency. However, the shortage of the mesoporous TiO2 is the ordered mesoporous structure can be badly destroyed in the crystalline process and TiO2 can only absorb the light less than 380 nm.In order to solve these problems in mesoporous titania photocatalyst, modification with doping agents can stabilize the structure of mesoporous TiO2, and improve its quantum efficiency and photoactivity in the visible light area. Besides, other method such as alcohol hydrolysis with surfactant free self-assembly methods are also used to prepare photocatalysts which have novel morphology and high photoactivity. The photocatalytic degradation of phenol, methylthionine chloride and bichrome in aqueous solutios are used as a probe to evaluate their photocatalytic activities. XRD, XPS, TEM, SEM, BET, PLS, RAMAN, IR, DRS of pyrodine adsorption and nitrogen-adsorption were used to characterize these photocatalysts. Their photocatalytic performances were discussed briefly from either their structural characteristics or surface electronic states. Lots of experiences were provided to further develop practical photocatalysis technique.The detail research work are listed as following:1. Preparation and photocatalytic activity of well-ordered mesoporous titania photocatalyst.According to the reported EISA method, we successfully prepared a series of well-ordered mesoporous titania photocatalyst by doping metal ions, and found different ion had different effect.(1) Doping rare earth metal ion La3+ can not only restrain the change of crystal phase in TiO2 and stabilize the structure of mesoporous TiO2, but also improve the photoactivity of photocatalyst, heat stabilization and crystallization of mesoporous TiO2 photocatalysts.(2) Doping noble metal Au, we can get complex substance of mesoporous Au/TiO2. It was found that TiO2 and Au both have very high crystallization, and Au nano-particles were well embedded in the mesoporous TiO2 wall structure to greatly improve the quantum efficiency and photocatalyst photoactivity.(3) We can get complex substance of mesoporous Bi/TiO2 by doping metal Bi. Bi2O3 can narrow the band gap of TiO2 from 3.2 eV to 2.7 eV to improve the ability of TiO2 to absorb visible light more effectively in photocatalysis process.Compared with the general TiO2, mesoporous structure TiO2 can improve the photoactivity. In the same condition, when the crystallization of TiO2 is in uniform, mesoporous TiO2 can have high surface area and avail for reactant transfer easily in the mesoporous pore. The sample which has the highly ordered mesoporous structure can have high photoactivity.2. Preparation and photocatalytic activity of core-shell structure titania photocatalyst by alcoholysis method.Structure-controlled core-shell TiO2 was synthesized by fast non-template method. The catalyst has a uniform structure and affluent surface structure. Through controlling the nucleation process, we get the core-shell micro-size TiO2 particles with good dispersity and stabilization in liquid, and get core-shell or shell structure catalysts by controlling the aging time. The structure has great influence in photocatalysis process, and the core-shell structure catalyst has the best activity due to the light can reflect between the core and shell, resulting in greatly improvement of light efficiency.更多还原