【作者】 宿艳；

【导师】 全燮； 陈硕；

【作者基本信息】 大连理工大学 ， 环境工程， 2009， 博士

【摘要】 TiO₂光催化氧化技术是一种有效的环境污染控制技术,近年来受到广泛的关注。负载型的TiO₂纳米膜可以解决粉体光催化剂的分离和回收困难等问题,但是较低的比表面积使其光催化活性降低,从而限制了它的实际应用。本论文以提高TiO₂纳米膜光催化效率为目的,制备了锐钛矿纳米颗粒膜和纳米线膜,研究了不同结构材料的可控性制备条件及其光催化性能;通过对TiO₂纳米管阵列膜进行元素硅的掺杂改性,提高TiO₂的紫外光催化效率;同时,采用光电催化氧化技术阻止光生电子和空穴的简单复合,有效提高了TiO₂纳米结构膜的光催化量子产率。本论文围绕以上内容,主要开展了以下几个方面的工作:（1）采用两步水热处理在钛基底上直接制备了锐钛矿TiO₂纳米结构（纳米颗粒或纳米线）膜电极。较低的水热温度下,制备得到由平均粒径小于15 nm的立方体和菱形体组成的锐钛矿纳米颗粒膜;较高的水热温度下,制备得到由单分散的锐钛矿纳米晶体和锐钛矿纳米晶体团聚体的集合体所组成的锐钛矿纳米线膜。X射线衍射（XRD）分析显示两种锐钛矿纳米结构膜均具有较高的锐钛矿结晶度;锐钛矿纳米结构膜所展现的显著的表面光电压响应和光电流密度表明它们具有很好的光电化学能力;紫外光照下,用锐钛矿纳米颗粒膜和纳米线膜对苯酚光电催化降解的动力学常数分别是致密TiO₂膜的2.2倍和3.4倍,并且苯酚的光催化和电化学过程之间存在着显著的协同效应。（2）采用液相进样的化学气相沉积（CVD）法在钛基底上制备了硅掺杂TiO₂纳米膜电极。这种液相进样的气相沉积过程所制备膜的平均沉积速率至少是由其它气相沉积过程所制备TiO₂膜沉积速率的10倍,而且元素硅在TiO₂膜中的掺杂量可以通过调配前驱体溶液中硅源的量而得以控制。实验分析表明元素硅掺杂到TiO₂纳米膜中,形成Si-O-Ti键,提高了TiO₂纳米膜的热稳定性,使得TiO₂在高温煅烧下仍具有较小的锐钛矿晶粒、更好的结晶度和提高的紫外光响应。与未掺杂的TiO₂纳米膜相比,硅掺杂量为5 at.%的TiO₂纳米膜在紫外光下降解苯酚的过程中展现了更高的光催化和光电催化活性,其降解苯酚的动力学常数分别是未掺杂TiO₂纳米膜的1.3和1.8倍。（3）以电化学阳极氧化制备的TiO₂纳米管阵列为基底,应用化学气相沉积法制备了硅掺杂TiO₂纳米管阵列膜电极。该电极具有高度有序的纳米管阵列结构,平均管长约为1μm;X射线光电子能谱（XPS）分析表明硅原子掺杂到TiO₂晶格中,形成Si-O-Ti键;XRD分析表明,硅掺杂能够抑制TiO₂的锐钛矿向金红石相的转换,并减小TiO₂纳米管的粒径;硅掺杂TiO₂纳米管的吸收边带相对于TiO₂纳米管蓝移了13 nm,且在紫外光区的吸收也明显增强;紫外光照下,硅掺杂纳米管阵列膜表面显示了超亲水性能。光电催化实验表明,硅掺杂TiO₂纳米管阵列电极对五氯酚的光电催化降解效率比未掺杂的TiO₂电极提高了84.8%。此外,应用直接电化学阳极氧化法制备了不同硅掺杂量的TiO₂纳米管阵列电极。该法既可实现元素硅掺杂,又可同时形成纳米管阵列,简化了实验过程。硅原子掺杂到TiO₂晶格中,形成Si-O-Ti键,并保持了纳米管阵列的形貌;硅掺杂可提高TiO₂的热稳定性,促使TiO₂在高温煅烧下仍以锐钛矿相为主,提高了锐钛矿相结晶度并形成小尺寸的锐钛矿微晶;硅掺杂也提高了TiO₂纳米管在紫外区的光吸收能力。相同实验条件下,所有硅掺杂电极的紫外光电流密度均高于未掺杂的TiO₂电极,其中硅掺杂量为4.2 at.%的电极性能最好,对五氯酚的光电催化降解率也最高。以上结果表明,制备具有独特构造的TiO₂纳米结构膜及对TiO₂纳米膜进行元素硅的掺杂改性可有效提高TiO₂的紫外光催化活性。同时,本文研究了纳米结构膜的形貌和元素硅掺杂量对TiO₂光催化能力的影响,为优化TiO₂光催化剂提供了可行的手段,有助于促进TiO₂光催化剂在环境污染控制领域中的应用与发展。更多还原

【Abstract】 Photocatalytic oxidation used TiO₂, one of the most attractive techniques for environmental pollution control, has been widely investigated. The immobilized TiO₂ nanofilm could solve the separation and recovery problems of powdery photocatalyst, but decreasing the photocatalytic （PC） activity due to its lower surface area, which hampers its practical application. In the present work, anatase nanoparticles film and nanowires film were prepared in order to improve the PC activity of TiO₂ nanofilm. The shape-tunable properties of synthesizable nanomaterials and their PC capabilities were investigated. The silicon modification could improve the ultraviolet PC activity of TiO₂ nanotube arrays film. Meanwhile, photoelectrocatalytic （PEC） oxidation can prevent the simple combination of photogenerated electrons and holes, consequently improving the PC efficiency of TiO₂. In this dissertation, some works were carried out as follows:（1） The nanostructured anatase film （NAF）, consisted of nanoparticles or nanowires, was fabricated directly on Ti substrate by a two-step hydrothermal approach. At lower hydrothermal temperature, a uniform film of anatase nanoparticles mainly consisted of nanoscale cubes and rhombohedra was fabricated. The average size of these nanoparticles was smaller than 15 nm. At higher hydrothermal temperature, anatase nanowires film which consisted of combination of monodispersed anatase nanocrystals and aggregates of anatase nanocrystals formed on Ti substrate. X-ray diffraction （XRD） analysis indicated that both NAFs possessed higher anatase crystallinity. The distinguished surface photovoltage responses and photocurrent densities of NAFs suggested that they had promising photoelectrochemical ability. The kinetic constants of PEC degradation towards phenol under UV light irradiation with NAF-nanoparticles and NAF-nanowires were 2.2 and 3.4 times as great as the values with CTF, respectively. A significant PEC synergetic effect between the photocatalytic and electrochemical processes was also observed.（2） The Si-doped TiO₂ nanofilm on Ti substrate was successfully prepared by chemical vapor deposition （CVD） with liquid injection. This method can control the Si-doping amount well by adjusting the precursor solution and obtain the rapid deposition rate of film. The average deposition rate of film prepared by this process was at least 10 times higher than that of TiO₂ film by other CVD processes. The analysis revealed that the introduced silicon might be incorporated into titania matrix and formed Si-O-Ti bonds. This incorporation helped to increase the thermal stability of titania, which was in favor of obtaining smaller anatase crystallites, higher crystallinity and enhanced UV absorption at high calcination temperature. The Si-doped sample with 5 at.% of silicon exhibited the best photoelectrochemical property, and its kinetic constants towards phenol degradation in PC and PEC processes under UV light irradiation were 1.3 and 1.8 times as great as the values for the undoped TiO₂ nanofilm.（3） The Si-doped titania nanotube arrays were fabricated by anodization, followed by CVD treatment. The obtained nanotube arrays show highly ordered and vertically oriented morphology, and the average length was about 1μm. Analysis by X-ray photoelectron spectroscopy （XPS） indicated that the introduced silicon might be incorporated into titania matrix and formed Si-O-Ti bonds. This incorporation helped to increase the thermal stability of titania, which suppressed the phase transformation of anatase and also inhibited the growth of anatase crystallite at high temperature. The Si-doped TiO₂ nanotube arrays showed an enhanced photoresponse in UV region and its absorption edge shifted 13 run to a higher energy. The surface of Si-doped sample showed a super-hydrophilic behavior under UV illumination. The Si-doped TiO₂ showed better PEC capability, its degradation rate for pentachlorophenol （PCP） under UV irradiation was 84.8% higher than that of undoped electrode. In addition, the Si-doped TiO₂ nanotube arrays with different Si-doping amounts were also fabricated by electrochemical anodization. This method provides a one-step way to implement the formation of nanotubes and Si-doping, which simplifies the preparation process. The results indicated the Si-doped nanotubes were highly ordered and vertically oriented on substrate. The introduced silicon might be incorporated into TiO₂ matrix and formed Si-O-Ti bonds, which was significant to improve thermal stability of TiO₂. Silicon doping facilitated in obtaining higher anatase crystallinity and small-sized anatase crystallite under high calcination temperature, and also enhanced absorption response in UV region. All the Si-doped electrodes showed the improved photoelectrochemical ability compared to the undoped one under UV illumination. The Si-doped sample with 4.2 at.% of silicon exhibited the best photoelectrochemical response and PEC degradation efficiency for PCP.The above results illuminated that the TiO₂ nanostructured films with unique architecture and modification of TiO₂ nanofilms with silicon can effectively enhance PC activity of TiO₂. The effects of morphologies of nanostructured films and silicon-doping amount on PC ability were also investigated, which was hoped to help optimize the PC capability of TiO₂ and develop TiO₂ photocatalyst in environmental pollution controlling.更多还原