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高浓度Ti3+自掺杂TiO2纳米晶的可控制备及其光催化性能研究
辛晓烨
学位类型硕士
导师王传义 ; 王兰
2015-05-28
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料物理与化学
关键词锐钛矿 Tiotio 2纳米晶 板钛矿 Ti 3+ 可见光 缺陷诱导光催化
摘要

二氧化钛(TiO2)纳米材料在过去的几十年是人们研究最广泛、最深入的金属氧化物材料,尤其是在能源和环境领域应用研究方面。然而,TiO2纳米材料的带隙较宽(约为3.2eV),对太阳能的利用率低,只能捕获占太阳光总能约5%的紫外光,这极大地限制了TiO2的太阳光利用率和它的实际应用。近期,人们研究了Ti3+自掺杂的TiO2,通过调控材料中的缺陷(如杂质或结构空位等)分布和浓度,能够得到所需的特殊功能,以解决TiO2在太阳光捕获效率和实际应用方面所面临的挑战,但目前存在合成条件苛刻、高能耗、多步骤等问题。为此,我们发展了氧化转化的方法(Ti2+→ Ti3+),通过简易的一步溶剂热/水热法制备了Ti3+自掺杂的锐钛矿/板钛矿相TiO2纳米晶;进一步煅烧处理,可控得到不同浓度和不同体相/亚表面分布的高浓度Ti3+自掺杂的TiO2纳米晶(500°C处理的样品Ti3+浓度高于目前文献报道的1.5倍),并具有优异的可见光催化活性。具体研究内容如下:(1)采用氧化转化的方法(Ti2+→Ti3+)得到钛的氧化物和氢氧化物的前驱体凝胶,通过简易的一步溶剂热法制备了Ti3+自掺杂的锐钛矿相TiO2纳米晶。详细探讨了前驱体凝胶的不同氧化状态、前驱体混合反应液的酸碱度对Ti3+自掺杂的锐钛矿相TiO2纳米晶的结构、形态和光催化性能的影响;进一步探索了通过HCl对溶剂热制备的纳米晶清洗处理的方法,以去除残余的NaBH4和NaBO2副产物等杂质;初步探索了形态结构与光催化性能优良的Ti3+自掺杂的锐钛矿相TiO2纳米晶的合成条件。(2)首次采用溶剂热-煅烧处理的方法获得了高浓度体相Ti3+自掺杂的锐钛矿TiO2纳米晶,通过温度的调控得到了不同浓度和Ti3+不同体相/亚表面分布的TiO2光催化剂。主要采用X射线光电子能谱(XPS)和电子顺磁共振谱(EPS)分析了样品表面Ti3+缺陷的化学态和浓度分布情况,并初步揭示了TiO2纳米晶中Ti3+缺陷的再分布及扩散动力学机理。500°C处理的样品,呈现出优异的性能,可见光降解亚甲基蓝效率和最大瞬态光电流密度分别为P25(德国EvonikDegussa生产的TiO2)的30倍和4倍。该部分研究阐明提高TiO2纳米晶中Ti3+缺陷的浓度以及控制Ti3+在其体相/亚表面的合理分布对有效提高TiO2的可见光催化活性具有重要意义。(3)通过水热合成的方法制备出Ti3+掺杂的单一相板钛矿TiO2纳米晶。在此基础上,采用简单的煅烧处理方法,可控制备了一系列不同浓度Ti3+掺杂的单一相板钛矿TiO2纳米晶。制备出的样品具有较高的稳定性和优异的可见光催化性能。用DMPO作为捕获剂,进一步研究了光催化反应过程中产生自由基的类型,为理解其光催化机理提供了理论基础。

其他摘要
Titanium dioxide (TiO2) has been a topic of extensively studied metal oxide materials in the last decades, especially in the arena of energy and environmental applications. However, its wide band gap (~3.2 eV) makes it capture only about 5% of solar energy, which greatly hinders its light harvesting efficiency. Recently, the chemistry of structurally defective TiO2 with Ti3+ self-doping (or oxygen vacancies) has been developed to tackle the above challenges. Well-managed defects (e.g. impurity, structural vacancies etc.) in terms of their location and concentration in materials can result in more desired properties. Based on this, we introduce an oxidation-based (Ti2+→Ti3+) synthesis of anatase/brookite TiO2 nanocrystals with various Ti3+ concentrations via a solvothermal/hydrothermal process in combination with post-annealing at different temperatures. The specific contents are as following: (1) The uniformed self-doped anatase TiO2 nanocrystals with high concentration of Ti3+ is synthesized by a oxidation-based solvothermal method, and we studied the H2O2 amount, acidic/weak alkali/strong alkali system dependence of precursor states and products formation. We also explored a HCl washing process to remove impurities, like unreacted NaBH4 and NaBO2 byproduct. (2) By simply controlling the annealing temperature, both concentration and location of the Ti3+ defects can be well managed to reside predominately in the subsurface/bulk regions of the post-annealed anatase TiO2 nanocrystals, a highly desired feature for stable visible light-driver photocatalysis. The location and quantity of the Ti3+ in anatase nanocrystals pinpointed by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) suggest that this temperature-mediated management of the location and concentration of Ti3+ defects is achieved through a Ti3+ reversible-diffusion mechanism. As an applicable verification, the sample attained by post-annealing treatment at 500°C, which has the highest Ti3+ concentration predominately in the bulk region, exhibits a 30-fold enhancement in visible-light decomposition of methylene blue and 4 times improvement in the maximal transient photocurrent density compared with P25. The present work underlines the importance of proper distribution of subsurface/bulk Ti3+ defects and give impetus to the development of the “defect engineering” of TiO2 nanocrystals towards high visible light-driven photoactivity. (3) Based on the hydrothermal synthesis method, we developed an effective strategy to prepare uniformed Ti3+ self-doped brookite TiO2 microcrystals. Through a post-annealing treatment, the location of the Ti3+ defects can be effectively controlled predominately in the subsurface/bulk regions of the brookite microcrystals, leading to the remarkably enhanced phocatalytic activity and stability. The type of free radicals produced in the visible-light decomposition of methylene blue process was explored using DMPO as a scavenger,providing insights on the visible ligth driver photocatalysis at Ti3+ self-doped brookite TiO2.
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4261
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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辛晓烨. 高浓度Ti3+自掺杂TiO2纳米晶的可控制备及其光催化性能研究[D]. 北京. 中国科学院大学,2015.
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