【作者】 蒋晶晶；

【导师】 蔡伟民；

【作者基本信息】 上海交通大学 ， 环境工程， 2011， 硕士

【摘要】 多年来,研究者拓展了许多关于提高TiO₂可见光催化性能的研究,然而,由于TiO₂的可见光催化性能会受到多种因素的影响,因此关于不少改性TiO₂所体现的可见光催化活性的机理研究还不够成熟。本文在低温下通过简易的回流法制备了两种具有可见光响应性能的TiO₂,通过一系列对照实验探索了引起其可见光催化性能的主要活性物质,并进一步解释了两者在可见光作用下催化降解甲基橙的机理。1.以钛酸四丁酯为钛源,在酸性条件下回流制备了具有良好可见光催化性能的TiO₂纳米颗粒。其晶相主要为锐钛矿结构,颗粒粒径小且分布范围窄,约为4⁵ nm。在该TiO₂的制备过程中,硝酸的参与不但能够促进TiO₂的胶化,抑制钛酸四丁酯的过度水解,还能够有助于TiO₂表面（尤其是锐钛矿（101）晶面）更多羟基的生成。在硝酸和正丁醇的协同作用下,TiO₂的晶粒表面容易在回流过程中形成烷氧基。一系列的对照实验和表征结果表明,表面烷氧基的形成是导致TiO₂具有可见光催化性能的主要原因。2.以钛酸四丁酯为钛源,采用简易的沉淀—氟化—回流晶化法在低温下制备了氟改性的TiO₂纳米颗粒（F-TiO₂）。颗粒形貌呈椭圆形,晶粒大小在5～8 nm。氟的引入不但有效抑制了板钛矿相TiO₂的生成,还从整体上提高了锐钛矿相TiO₂的晶化度;样品中的氟主要分布在TiO₂表面,以化学吸附态为主,并伴有少量的间隙氟。当以甲基橙作为降解底物时,实验制得的F-TiO₂在可见光下显示出了较强的催化性能。研究发现,F-TiO₂在可见光下对甲基橙的降解并不是由晶格氟离子或氧空位引起的,而是源于TiO₂表层吸附态氟离子和间隙氟离子的协同作用。3.两种形式的改性TiO₂对有机底物的可见光降解都是由其表面态引起的。经表面烷氧基改性的TiO₂能够通过LMCT过程被可见光激发,进而产生对其他有机底物的降解能力;而经氟离子改性的TiO₂对甲基橙的高效降解是源于由表面氟和间隙氟协同增强的染料自身敏化作用。因此,在研究拓展具有可见光响应能力的TiO₂时,必须充分考虑到在TiO₂制备过程中可能形成的表面态,并且有必要对不同结构有机物的光降解进行比较,以助于深入理解其可见光催化性能的本质。更多还原

【Abstract】 In recent years, much effort has been made to development visible-light activated TiO₂-based materials. However, as the visible-light activity of titania could be affected by many factors, the mechanism study of some visible-light activated ion-modified TiO₂ catalysts are always in depute. In this study, we developed two kinds of surface-modified TiO₂ catalysts through a facile low-temperature refluxing method, both of which have obtained an effective visible-light activity in the degradation of methyl orange （MO）. Through a serious of experiments, we investigated the substances which caused the visible light activity of titania, and tentatively discussed the degradation mechanism of MO under visible light on these two catalysts.1. A visible-light responsive anatase TiO₂ was synthesized through a peptizing-reflux method, using tetrabutyl titanate as the titanium precursor. The catalyst is mainly anatase, and composed of spherical-shaped nanoparticles （4～5 nm）. We observed that in the synthetic process of TiO₂ catalysts, the nitric acid not only helps to peptize the titania, promote the formation of surface hydroxyl groups, but also inhibited the over-hydrolysis of tetrabutyl titanate; the presence of acid and hydrolysis products （n-butanol） cooperatively lead to the retention of more alkoxyl groups on the anatase surface, which is proved to be the main cause of the visible light activity.2. A fluorine-modified nanosized TiO₂ （F-TiO₂） was prepared through a precipitation -fluorination-reflux method. The results showed the small particle size （5～8 nm） of ellipsoidal shaped F-TiO₂ samples. The presence of fluorine not only suppressed the formation of brookite phase, but also improved the crystallinity of anatase phase. The fluorine atoms mainly distributed on the surface of TiO₂, and existed in both forms of chemical- adsorption and interstitial-doping. Compared to the pure titania, the fluorine-modified TiO₂ powder showed much higher degradation efficiency of methyl orange （MO） under visible light. Further investigation showed that the increased degradation rate of MO under visible light caused by the synergistic effect of chemical-adsorption and interstitial-doping fluorine atoms. 3.The visible-light degradation of MO on the two kinds of modified TiO₂ catalysts was actually caused by surface states. On the alkoxyl-derived surface states, excited electrons could be generated and transfered easily through a ligand-to-metal charge transfer （LMCT） process under visible light irradiation. However, the degradation of MO on F-TiO₂ samples was actually caused by the enhanced self-degradation of dye on the surface states formed by fluorine atoms. Therefore, in the research of visible-light activited TiO₂ catalysts, the surface states of titania formed in the synthetic process should not be neglected; besides, the investigation on the degradation efficiency of different substrates is also essential to fully understand the intrinsic property of surface-modified TiO₂ catalysts.更多还原