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M/TiO2(M = Au,Ag)复合材料的微结构调控及光催化性能研究
Thesis Advisor王传义、王富
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline材料工程
KeywordTio2 复合材料 光催化 金属 微结构

在能源和环境领域,TiO2是学者们最感兴趣的金属氧化物半导体材料之一,TiO2在许多方面的应用与其光吸收性能及载流子分离效率紧密相关。然而,TiO2作为光催化剂,经常会受到其较宽的带隙(~ 3.2 eV)及快速复合的光生载流子限制。本论文通过调控TiO2的表面微结构,并在其表面负载贵金属,成功地构建了M/TiO2(M = Au,Ag)复合体系;增强了TiO2在可见光区域的吸收,同时提升了光生载流子的分离效率。具体研究内容如下: (1)分别用三种不同钛源合成了TiO2光阳极,不同钛源得到TiO2光阳极的形貌不同。线性扫描和光电流测试表明具有分级结构的TiO2纳米线/微米花(Hierarchical TiO2 nanowires/microflowers,H-TiO2)光电极具有较好的光电催化分解水的能力,归因于其较大的溶液接触面积及大量的活性位点,以及快速传输电子的能力。进一步的研究表明,钛源前驱体对于调控TiO2分级结构的形成起着关键性的作用。(2)通过光化学法构筑了Au/H-TiO2复合体系,Au的负载量对于其光电催化效率有很大的影响:在Au/Ti质量比约为0.231%时,Au/H-TiO2达到最大的光转化效率,约为纯TiO2的3倍。Au/H-TiO2光转换效率的提高归因于其相对较长的电子寿命和优异的电荷分离效率。与此同时,稳定性测试表明Au/H-TiO2复合体系具有优异的光稳定性和长期光电催化水氧化的实用性。另外,光电转化效率测试结果说明,Au/H-TiO2在可见光区光活性的增强是由于“热”电子效应。本章工作提供了一种构筑高效光电催化水分解的金属/半导体电极体系的新方法。(3)通过光还原及简单的后退火处理合成了表面具有氧空位的Ag-TiO2 ? x光催化复合材料。沉积的Ag纳米颗粒增强了体系的光吸收能力及光生载流子的分离效率。与商业P25相比,Ag-TiO2 – x不仅具有优异的光催化祛除NO能力,而且可以有效抑制毒性更大的NO2的产生。研究表明,在光催化祛除NO过程中,NO的光氧化以及NO选择性还原为N2这两个反应同时发生。氧化过程是由于h+和?O2?的协同效应,选择性还原反应是由于后处理过程引入的氧空位的作用。另外,不同波长光下的NO祛除测试,进一步说明Ag的等离子共振吸收峰与可见光下光催化活性增强紧密相关。本章工作提供了一种设计能够在可见光下高选择性祛除NO的光催化剂的新方法。

Other Abstract

TiO2 has become one of the most attractive metal oxide semiconductor materials, especially in the fields of energy and environmental applications. In addition, its applications in many aspects are closely related with its optical absorption and carriers separation efficiency. However, utilization of TiO2 as a photocatalyst is usually limited by its wide band gap (~ 3.2 eV) and fast recombination of photoinduced charge carriers. In this thesis, we successfully construct the M/TiO2 (M = Au, Ag) composites by tuning the microstructure of TiO2 and depositing noble metal onto the surface of TiO2. Undoubtedly, compared with the bare the TiO2, the light absorption and charge separation efficiency of M/TiO2 (M = Au, Ag) composites are significantly enhanced. The specific contents are as following: (1) Three different kinds of titanium precursors were used to prepare TiO2 photoanodes, the morphologies of the obtained samples are completely different. Linear sweep voltammetry (LSV) and I-t measurements all indicate that the H-TiO2 photoanode posseses the best photoelectrochemical (PEC) performance among these three photoanodes. This photoanode simultaneously possesses a large contact area with electrolyte, a large amount of active sites, and a rapid electronic transport path, contributing to its superior PEC performance. Furthermore, the initial concentration of titanium precursors plays a key role in the formation of the hierarchical structure.(2) Au/H-TiO2 composites were fabricated by a photochemical method. The loading amount of Au plays a vital role in the PEC performance of these photoanodes. The maximum photoconversion efficiency was achieved when the weight ratio of Au/Ti is about 0.231%, which is about 3 times higher than that of the pristine H-TiO2. The enhanced photoactivity of Au/H-TiO2 can be attributed to the relatively longer electron lifetime and efficient charge separation efficiency in comparision to the bare H-TiO2. Meanwhile, the stability test illustrates that this system has remarkable photostability and excellent practicality for long-term PEC water oxidation. In addition, the results of incident photon-to-current conversion efficiency measurement illustrates that the enhanced photoactivity of Au/H-TiO2 in the visible region is mainly caused by “hot” electrons. The present work signifies the rational design of the metal/semiconductors system as a new avenue of preparing efficient photoelectrodes for PEC water splitting. (3) Ag-TiO2 ? x nanocomposite was successfully synthesized via a facile photochemical reduction process followed by post-annealing. The deposition of Ag nanoparticles significantly increases the light absorption and charge separation. Compared with commercial P25, the Ag-TiO2 ? x nanocomposite is not only superior in visible-light photocatalytic NO removal, but also in inhibiting the production of NO2, whose toxicity is 4?5 times higher than that of NO. As confirmed by gas chromatography and FTIR measurement, the photo-oxidation of NO and selective photo-reduction of NO to N2 occur simultaneously during the process of NO removal by Ag-TiO2 ? x. The oxidation of NO was due to the synergic effect between h+ and ?O2?; while the selective photo-reduction was resulted from introduced oxygen vacancies in TiO2. In addition, the light wavelength dependence measurement reveals that the surface plasmon resonance effect of Ag is responsible for the improvement of the visible-light photoactivity. The present study will provide an alternative approach to design highly selective photocatalysts for NO removal under visible-light.

Document Type学位论文
Recommended Citation
GB/T 7714
段燕燕. M/TiO2(M = Au,Ag)复合材料的微结构调控及光催化性能研究[D]. 北京. 中国科学院大学,2017.
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