【作者】 荆洁颖；

【导师】 李文英； William W.Yu；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2012， 博士

【摘要】 纳米TiO2光催化氧化技术可在常温常压下通过氧化还原反应将有机难降解污染物彻底氧化成H2O, CO2和无机盐类。相比于目前常用的生物法和物化法等降解技术,光催化氧化技术因其所用纳米TiO2具有氧化性强、耐酸碱性好、化学性质稳定、对生物无毒、来源丰富等优点在处理难降解有机物方面受到广泛重视。然而,由于纳米TiO2颗粒细微,在光催化过程中易失活、分散不均匀、易团聚、难以分离回收；以及锐钛矿型TiO2是宽禁带半导体,仅能响应短波长的紫外光,以太阳光做光源时,在室外只能吸收太阳光中不到5%的紫外光部分,能源利用效率低,光催化的过程以人工紫外光为主,技术适应性差、成本高,在工业应用过程中受到很大限制。因此,提高纳米TiO2的光催化活性、增强其在水溶液中的分散性和稳定性、解决纳米颗粒分离回收的问题并实现纳米TiO2的高可见光催化活性是Ti02光催化氧化技术工业化应用过程中最具挑战性的课题。本课题以高活性、高水分散纳米TiO2光催化剂的设计、制备及结构与性能研究为基础,以降解氮杂环化合物喹啉的反应为应用平台,研究了纳米TiO2光催化剂的物化特性与其相应的光催化特性、喹啉光催化降解的途径和方式。主要结果和结论如下：(1)表面Zeta电位-40mV,粒径为9.8±0.6nm的高水分散锐钛矿型纳米Ti02的低温制备。以静电位阻理论为指导,在促进钛醇盐水解的思路引导下,不添加表面活性剂在低温(80℃)制备得到水分散良好的锐钛矿型纳米Ti02；采用透射电镜(Transmission Electron Microscope, TEM), X-射线衍射仪(X-ray diffractometer, XRD),X-射线光电子能谱(X-ray photoelectron spectroscopy, XPS),傅里叶红外(Fourier Transform Infrared Microscope, FTIR)和动态光散射(Dynamic Light Scattering, DLS)等表征手段对其形貌、结构、表面特性及稳定性进行分析,得知该纳米TiO2的高水分散性源于其表面形成的双电层；通过对不同制备方法得到的纳米TiO2结构及其水分散性的比较,发现不同制备方法得到的纳米TiO2因其表面特性的差异最终导致水分散性的不同,进一步验证了不添加表面活性剂低温合成水分散纳米TiO2颗粒的优越性。(2)粒径5-30nm水分散超顺磁性纳米Fe304颗粒的可控制备。采用高温热解羧酸盐结合相转移的方法及一步反向沉淀法成功制备了一系列水分散性好、形貌粒径可控、表面官能团可调、化学性质和晶型稳定的纳米Fe3O4颗粒。其中一步反向沉淀法因其所用原料便宜易得、无污染,提供了一种环境友好型制备水分散性纳米Fe3O4颗粒的方法。所制备的纳米Fe3O4颗粒不仅在催化剂分离回收方面有重要作用,而且由于对纳米Fe3O4颗粒表面官能团进行了可控合成,对其在核酸分析、临床诊断、靶向药物、酶固定化等方面的应用也具有极大的推动作用。(3)可磁分离回收磁载纳米Ti02光催化剂的低温制备。基于一步反向沉淀法制备得到的纳米Fe304颗粒,结合制备水分散纯纳米Ti02的方法,以静电位阻理论为指导,在低温下制备得到可磁分离回收的磁载纳米Ti02光催化剂。该法避免了传统制备过程中·热处理带来的颗粒长大、比表面积下降及团聚问题。制备过程中通过调节Fe3O4/TiO2摩尔比可实现对产物形貌、晶型、表面特性及磁性能的调控。(4)可见光响应TiO2/氧化石墨烯复合光催化剂的低温制备。采用改进的Hummers了法结合超声波辅助制备得到氧化石墨烯,结合不添加表面活性剂制备水分散纯纳米TiO2颗粒的方法,在低温下制备了TiO2/氧化石墨烯复合光催化剂。氧化石墨烯的添加对TiO2的可见光化有很大影响。随着氧化石墨烯含量的增加,TiO2/氧化石墨烯复合光催化剂的吸收边带发生明显红移,拓展了其可见光响应范围。TiO2/氧化石墨烯复合光催化剂中Ti以Ti4+形式存在,且TiO2/氧化石墨烯复合物中氧化石墨烯和TiO2之间没有形成Ti-C键。(5)不同纳米TiO2光催化剂光催化活性评价。以TiO2光催化降解氮杂环化合物喹啉的反应为应用平台,研究了所制备水分散纯纳米TiO2光催化剂、磁载TiO2光催化剂和可见光响应TiO2光催化剂的光催化活性与结构之间的关系。在水分散纯纳米TiO2光催化剂体系中发现：制备方法的不同会导致催化剂物化性质的差异,进而影响纳米TiO2光催化剂的活性；实验发现在紫外光照射下,TiO2以·O2为主要活性自由基物种光催化降解喹啉,而非通常认为的“有机物降解一般以·OH为主要自由基”。在磁载纳米TiO2光催化剂体系中发现：Fe3O4与TiO2相对含量(即催化剂的组成)对磁载TiO2光催化剂的光催化活性有较大影响,通过调节Fe3O4与TiO2相对含量可实现对其光催化活性的调控。在可见光响应TiO2光催化剂体系中发现：氧化石墨烯的添加对纳米TiO2的可见光响应活性具有重要影响,光催化反应过程中氧化石墨烯可作为电子受体,抑制光生电子-空穴的复合,而且其大的比表面积有利于喹啉在催化剂表面的吸附,从而使得TiO2/氧化石墨烯复合光催化剂的可见光催化活性及稳定性较高。更多还原

【Abstract】 Photocatalytic oxidation can be carried out under ambient conditions using atmospheric oxygen as the oxidant and leads to complete mineralization of pollutants to CO2, water and mineral acids. It is a promising alternative to biological and physical methods because the used nanocrystalline titanium dioxide (TiO2) in photocatalytic oxidation not only possesses high chemical and biological inertness, non-toxicity and relative low cost, but also has other distinctive properties of nanoparticles such as quantum effect and superior catalytic performances, etc. However, TiO2nanoparticles are prone to lose activity and aggregate in photocatalytic process due to its small size, and the difficulty in separating TiO2nanoparticles from the treated water is also ascribed to the fine TiO2nanoparticles. Moreover, anatase TiO2absorbs only around5%ultraviolet part of solar light because of its wide band gap, and artificial light sources are expensive and unstable. All of them are the main barriers to marketing TiO2photocatalytic oxidation.This dissertation focuses on the synthesis, characterization and photocatalytic application of highly water-dispersible TiO2nanoparticles. On one hand, in order to overcome the barriers in TiO2practical application, many efforts were made to exploit new synthetic strategies to obtain TiO2nanoparticles with desirable property. On the other hand, in order to achieve industrial photocatalytic application of TiO2nanoparticles, valuable investigations have been conducted on the relationship among preparation approach, crystal structure, size and photocatalytic performance. The photocatalytic performance of the as-synthesized TiO2nanoparticles were evaluated for the degradation of quinoline as a model pollutant. The photodegradation mechanism of quinoline was also studied. The main findings are as follows:(1) Low-temperature synthesis of water-dispersible anatase TiO2with zeta potential-40mV and average size of9.8±0.6nm. According to the classical theory of Derjaguin, Landau, Verwey and Overbeek (DLVO), water-dispersible anatase TiO2nanoparticles were synthesized at a low temperature (80℃) without any organic surfactants via the mechanism of electrostatic repulsion between nanoparticles. TEM (Transmission Electron Microscope), XRD (X-ray diffractometer), XPS (X-ray photoelectron spectroscopy), FTIR (Fourier Transform Infrared Microscope) and DLS (Dynamic Light Scattering) were used to characterize its morphology, crystallographic structure, surface property and stability etc. By comparing the structure and water-dispersibility of TiO2nanoparticles synthesized by different approaches, it is found that preparation approach would lead to variation in the surface property of TiO2nanoparticles, which finally resulted in the different water-dispersibility of TiO2nanoparticles. This result further proves the advantage of low temperature synthesis of anatase TiO2nanoparticles without any organic surfactants.(2) Controllable synthesis of water-dispersible magnetite nanoparticles with size range from5to30nm. Ligand-exchange approaches and one-step reverse precipitation method were developed to synthesize monodisperse, water-dispersible and carboxylate/amino-functionalized superparamagnetic magnetite nanoparticles. Hereinto, one-step reverse precipitation method uses commercial available, inexpensive, and environmentally acceptable raw reaction materials (water is the solvent), obviously, it provides an economic and green approach for the controlled synthesis of magnetite nanoparticles. The as-synthesized magnetite nanoparticles not only play a vital role in catalyst recycle, but also accelerate its biomedical applications, such as magnetic resonance imaging, drug delivery and bioseparation because of their tunable surface functional group.(3) Low temperature synthesis of magnetically separable Fe3O4/TiO2composite photocatalysts. Based on the coulomb electrostatic forces between Fe3O4and TiO2, magnetically separable Fe3O4/TiO2composite photocatalysts with different molar ratios of Fe3O4to TiO2were synthesized via a modified sol-gel method at low temperature of80℃. This approach avoids the high temperature calcination involved in traditional methods, which usually results in the grain growth and aggregation of the resultant products and therefore the loss of surface area. The morphology, crystal structure, surface property and magnetic performance of the as-synthesized magnetically separable Fe3O4/TiO2composite photocatalysts could be controlled by changing the molar ratios of Fe3O4to TiO2.(4) Low temperature synthesis of visible light responsed TiO2photocatalyst. Graphene oxide (GO) was synthesized via improved Hummers method with the help of ultrasonic treatment. TiO2/GO composite photocatalyst were synthesized based on the synthetic procedure of water-dispersible TiO2nanoparticles without any organic surfactants. GO greatly contributes to its visible-light response. With the increase of GO quantity, the absorption band of TiO2/GO composite presents obvious red shift, correspondingly, the band gap become narrower, and finally the absorption range of visible-light was extended. In TiO2/GO composite photocatalyst, Ti was existed in the form of Ti4+, and there is no formation of Ti-C bond.(5) The photocatalytic application of the as-synthesized TiO2nanoparticles were investigated for the degradation of quinoline as a model pollutant. For the pure water-dispersible TiO2nanoparticles, it is found that different preparation approach could lead to the change in the physical and chemical properties of TiO2nanoparticles, and finally influence the photocatalytic activity of nanoparticles. In this work, we found that the superoxide radical (·O2) played an important role in the photodegradation of quinoline, which is greatly different from most of other publication. For magnetically separable Fe3O4/TiO2composite photocatalysts, it is found that the relative quantity of Fe3O4to TiO2can greatly affect the photocatalytic activity. The Fe3O4/TiO2composites could be easily recovered from the reaction solution by using a permanent magnetic bar and their photocatalytic activity changed little after repetitive uses. For TiO2/GO composite photocatalyst, GO greatly contributes to its visible-light response. GO can be acted as electron-acceptor and inhibit the recombination between photogenerated electron-hole. Its large specific surface area is beneficial to the adsorption of quinoline on the catalyst surface. These factors endow the TiO2/GO composite photocatalyst high and stable photocatalytic activity.更多还原