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金属氧化物纳米片的改性及其协同效应研究
刘鹤
学位类型博士
导师张海涛
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词金属氧化物纳米片 二维纳米复合材料 协同效应 催化 Co2吸收
摘要

能源短缺和环境污染问题的日益严重使得开发和使用清洁能源越来越受到重视,因此开发高活性、高选择性的高效纳米功能材料变的尤为重要。近年来二维(2D)纳米材料的迅速发展为设计合成具有特殊性质和各种功能的新型纳米复合材料提供了新的契机。2D金属氧化物纳米片的高度各向异性和超薄厚度使其具有特殊的电子结构和物化性质,大量暴露的表面原子也使其易于进行修饰、杂化和组装,所获得的复合材料不仅具有可调的物化性质,且各组分间的协同耦合作用还能产生很多奇异的表界面性质和功能。本论文的研究从金属氧化物纳米片入手,将其与石墨烯、离子液体(ILs)以及金属元素等进行复合,制备出一系列基于过渡金属氧化物纳米片的新型多功能2D复合材料,研究组装修饰对纳米片物化性质(形貌、晶体结构、电子结构、能带结构及酸性质等)的影响,并结合能源与环境领域重要的应用对所合成的2D复合材料进行应用评价,重点考察复合材料微结构与复合组分间协同性能之间的构效关系,主要的创新性工作如下:1. 将2D超薄的HNb3O8纳米片与石墨烯进行复合,二者交错堆叠形成具有大量异质界面和多级孔结构的新型复合层状多孔材料。将其应用于CO2的光催化还原,在最佳HNb3O8纳米片/石墨烯复合比下,复合物对CO2光催化转化为CO的产率比商业化的P25提高8.0倍,比HNb3O8块体材料提高8.6倍。对材料微结构与催化性能间的构效关系研究表明,HNb3O8纳米片和石墨烯之间的强相互作用使得复合材料比表面积增大、带隙变窄、光生载流子复合速率下降、酸强度和酸量增加,从而获得优异的光催化性能。该工作表明合理设计和可控合成以金属氧化物纳米片为基本结构单元的新型层状复合材料,不仅可以调控2D复合材料的物化性质和催化性能,并且有助于从分子尺度上理解纳米材料微结构与性能之间的构效关系以及组分间的协同作用机制。2. 通过剥离/离子交换的方法合成出一种高效的Fe掺杂HTaWO6(TaW-Fe)纳米管固体酸催化剂。Fe3+与纳米管之间的强相互作用能够明显提高纳米管的结构/热稳定性,使纳米管在高温焙烧时可以保留大部分的酸性位点,并且这种相互作用还有利于生成新的酸性位点。这些因素协同作用使TaW-Fe纳米管焙烧后仍保持很高的固体酸催化活性(苯甲醇和苯甲醚的Friedel?Crafts烷基化反应以及醋酸和乙醇的酯化反应),因此这种结构稳定的固体酸纳米管在反应条件苛刻的固体酸催化反应中具有良好的应用前景。进一步对HTaWO6纳米管进行Mn、Co、Ni、Cu、Zn几种金属元素的掺杂,研究了不同元素掺杂对纳米管物化性质及结构/热稳定性的影响,进而考察各金属元素掺杂对HTaWO6纳米管酸性质及固体酸催化性能的影响,为合理设计高性能固体酸催化剂提供新思路。3. 将TiO2纳米片与不同碳链长度的咪唑型ILs进行复合,制备出TiO2-ILs层状有机?无机纳米复合物,研究咪唑阳离子碳链长度对纳米片表界面性质的影响,并考察复合材料表界面性质与CO2吸收性能之间的构效关系。结果表明,咪唑阳离子碳链长度会影响ILs与纳米片之间作用力的大小,改变复合材料的层间距,进而影响复合材料的形貌、物化性质及CO2吸收性能。随着复合咪唑阳离子碳链的增长,TiO2-ILs复合物对CO2的吸收性能有所提高。分析表明,复合物层间水分子的含量、层间可供CO2吸附的自由空间大小、咪唑阳离子与无机纳米片之间作用力大小等因素共同影响层状复合材料的CO2吸收性能。2D无机纳米片与ILs的结构整合和界面调控为合成具有能源环境应用前景的新型层状纳米复合物提供了研究思路。

其他摘要

There has been an increase in the use of clean and renewable energy due to the growing concern about energy shortage and environmental pollution. Hence, it is inevitable to exploit highly efficient functional nanomaterials with desirable activity and high selectivity. Recently, the rapid development in two-dimensional (2D) nanomaterials brings about new breakthroughs in designing of new-generation multifunctional nanocomposites with fascinating properties and potential applications. 2D metal oxide nanosheets exhibit unique electronic structure and distinctive physicochemical properties arising from their molecular thickness and extremely high 2D anisotropy. The fully exposed surface atoms render them easy to hybridize with other nanomaterials to create novel assemblies and hierarchical structures. The hybridization can not only tailor their physicochemical properties, but also create unexpected functionality via a synergetic coupling between the components.In this thesis, we intend to reorganize metal oxide nanosheets with graphene, ionic liquids (ILs), and metal elements to fabricate novel 2D nanocomposites. The synergetic effects of hybridization on the physicochemical properties (such as morphology, crystal structure, electronic structure, energy band structure, and acidity) of nanosheets were fully investigated. These functional 2D composites were also applied into energy and environmental fields to clearly probe the relationships between the microstructures of nanohybrids and their performances. The main results are summarized below:1. Layered HNb3O8/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores were fabricated via the alternative stacking of HNb3O8 nanosheets with graphene nanosheets. When applied in the photocatalytic conversation of CO2 into renewable fuels, the optimized HNb3O8/G hybrids yielded 8.0-fold and 8.6-fold improvements in CO evolution amounts than that of commercial P25 and HNb3O8 bulk powders. The improved photocatalytic performance is attributed to the exotic synergetic effects via the combination of enhanced specific BET surface area, narrowed band gap energy, depressed electron-hole recombination rate, as well as increasing strong acid sites and strong acid amounts. This work demonstrates that rational design and controllable synthesis of layered nanohybrids based on metal oxide nanosheets can not only tune the physicochemical properties and photocatalytic performance of the nanohybrids, but provide a better understanding of the relationships between the microstructures of nanohybrids and their synergetic performances at the molecular level.2. Fe-doped HTaWO6 nanotubes as highly active solid acid catalysts were prepared via an exfoliation-exchange process. Doping Fe ions into the nanotubes endowed them with an improved structural and thermal stability due to the stronger interaction between intercalated Fe ions and the host layer. This interaction also preserved the effective Br?nsted acid sites of nanotubes upon calcination and facilitated the generation of new acid sites. The integration of these functional roles resulted in Fe-doped nanotubes with high acidic catalytic activities in the Friedel?Crafts alkylation of anisole and the esterification of acetic acid. Due to their improved catalytic activity and stability, Fe-doped nanotubes can be used as solid acid catalyst in harsh conditions. Moreover, Mn, Co, Ni, Cu, and Zn were doped into HTaWO6 nanotubes to investigate the effect of doped metal species on the acid properties and acidic catalytic performance of nanotubes. This can shed new lights on rationally designing solid acid nanohybrids with superior catalytic performance.3. Layered inorganic-organic TiO2-ILs hybrids were fabricated through intercalating imidazolium-based ILs into 2D titanate nanosheets. The effects of cation sizes on the interfacial properties and CO2 uptake capacity of hybrids were comprehensively investigated. The results indicated that the length of carbon chain can modify the interlayer spacing of the hybrids by regulating the interaction strength between ILs and the host nanosheets, thus leading to the variation in morphology, physicochemical properties and CO2 uptake capacity. As a result, TiO2-ILs compounds displayed enhanced CO2 absorption capacity with the increasing carbon chain length, owing to the synergistically interfacial effects induced by water contents and free space in interlayer region, as well as diverse interactions of ILs with inorganic nanosheets. The structural integration and interfacial regulation of 2D inorganic nanosheets with ILs will provide a protocol to develop novel layered nanocomposites for energy and environmental applications. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24229
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刘鹤. 金属氧化物纳米片的改性及其协同效应研究[D]. 北京. 中国科学院研究生院,2017.
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