【作者】 曹敏纳；

【导师】 曹荣；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2011， 博士

【摘要】 本论文探索了利用瓜环作为稳定剂和载体来制备具有潜在应用价值的高效纳米催化剂。基于瓜环的纳米催化剂的设计、制备和催化性能的研究证明,瓜环是一种优良的纳米材料稳定剂和载体。课题的设计思路是基于瓜环不易溶于常见溶剂、较高的热稳定性和化学稳定性、结构上的高度对称性等特点。这些都是传统纳米颗粒稳定剂和载体所不具备的特色。本论文的主要研究内容如下:1.利用不同构成单元数目的瓜环制备了四种钯纳米颗粒,CB[n]-Pd NPs(n=5,6,7,8)。瓜环的端口羟基与纳米颗粒表面原子之间的静电相互作用起到了稳定钯纳米颗粒的作用,同时利用瓜环的难溶性对钯纳米颗粒起到负载作用。研究了不同瓜环制备得到的钯纳米颗粒形貌特征,并探讨了不同瓜环如何因结构上的差异导致钯纳米颗粒形貌、分散度以及粒径大小等方面的差异。通过调节六元瓜环与金属前驱体之间的比例,制备了不同形貌的钯纳米颗粒,初步实现了基于瓜环的钯纳米颗粒的形貌控制。采用不同的还原方法可制备了孪晶面丰富、形状各异的基于瓜环的钯纳米颗粒,实现了钯纳米颗粒的形貌控制。2.探索了基于瓜环的钯纳米颗粒对碳碳偶合反应的催化效果。基于瓜环的钯纳米颗粒可以在醇/水体系中,较为温和的条件下高效催化Suzuki偶合反应。研究了催化Heck反应的条件,实现了对链状烯烃和卤代芳香烃的高效催化。3.利用不同的还原方法制备了四种基于瓜环的铂纳米颗粒,根据TEM、XRD等表征,详细分析了四种铂纳米颗粒的形貌特征。通过简单的合成手段制备出四种形貌新颖的铂纳米颗粒:1)具有较高比表面积和形貌复杂的三维铂纳米花;2)具有丰富孪晶面和堆叠层错结构的铂纳米颗粒;3)枝状生长的铂纳米颗粒;4)粒径~2 nm并且分散均匀的铂纳米颗粒。提出了不同形貌铂纳米颗粒的相应生长机理,进一步验证了瓜环在纳米材料制备过程中的独特优势。4.研究了基于瓜环的铂纳米颗粒的电化学性能。这种瓜环的铂纳米颗粒在对甲醇的电催化氧化中表现出较低的起始电势、高的电流密度以及If /Ib比值,是催化活性较高的、抗中毒能力较强的电催化剂。同时还研究了基于瓜环的钯纳米颗粒对甲酸的电化学性能,两种钯纳米颗粒都表现出较强的电催化能力。电化学性能的研究进一步说明了基于瓜环的纳米颗粒表面活性位点暴露充分,具有较高的催化活性。5.通过原位法合成了一种基于瓜环和多酸为基元的有机-无机杂化材料,CB[6]-POMs。通过单晶结构解析以及红外吸收等表征对该杂化材料的结构进行了深入的研究,发现通过氢键网络紧密联系有机构筑单元和无机构筑单元形成了有机-无机的超分子结构。该氢键网络还实现了电子在有机、无机构筑单元之间的传递,在可见光照射下,CB[6]为主的有机构筑单元作为光敏剂,电子跃迁至多酸为主的无机构筑单元的LUMO轨道并引发分子氧等生成相应自由基,最终实现光催化降解染料分子。CB[6]-POMs能够在可见光下对染料分子的光催化降解,是对多酸光催化剂可溶以及不可利用可见光等缺陷的弥补,同时也是瓜环在环境保护方面的重要应用。更多还原

【Abstract】 The goal of this dissertation is to study the fabrication of nanocatalysts with high catalytic activities by using cucurbit[n]uril (CB[n], n=6) as stabilizer/support. CB[n] is a class of excellent stabilizer and support for nanomaterials, which are verified by experiments involving the design, preparation and performance investigation of nanocatalysts based on such material. The design of the projects is based on its insolubility in common solvents, high thermal stability, chemical stability, and symmetrical structure of CB[n]. The details are summarized as follows:1. Four types of palladium nanoparticles, CB[n]-Pd NPs (n=5, 6, 7, 8), were prepared using four different kinds of CB[n]. Pd nanoparticles can be stabilized by the electrostatic interactions between the surface atoms of the nanoparticles and the carbonyl-laced portals of CB[n]. CB[n] also acts as the support for the nanocatalysts due to its insolubility in common solvents. The morphologies of different CB[n]-Pd NPs (n=5-8) studied. The investigation concerning the differences of appearance, dispersity, and particle diameter were also carried out. Pd NPs with controlled shapes and size were prepared by changing the molar ratio of CB[6] to metal precursor. Additionally, many reduction methods were utilized to attain CB[n]-Pd NPs with different shapes and rich twinned planes.2. The catalytic performances of CB[n]-Pd NPs (n=6, 7) for C-C coupling reactions were investigated. With ethanol/water as solvent, Suzuki reactions proceeded smoothly under mild conditions. The conditions for the Heck reactions were also tested. Up to 99% yield was obtained employing aryl halides and chain olefins as the coupling partners in the presence of CB[6]-Pd NPs.3. Four different CB[6]-Pt NPs were fabricated using different reduction methods, and their morphologies were studied based on TEM and XRD. In addition, four Pt NPs with novel morphologies were synthesized via simple procedure: 1) Pt nanoflowers with 3D complicated surface structures and high surface area; 2) Pt nanoparticles with rich twinned planes and stacking faults; 3) Pt nanoparticles with branch; 4) Pt nanoparticles with good dispersion and with particles size less than 2 nm. The growth mechanisms of CB[6]-Pt NPs with different morphologies were proposed, which further demonstrated the unique merits of CB[n] in the fabrication of nanoparticles.. 4. The electrochemical performance of CB[6]-Pt NPs were studied. Such nanoparticles showed low onset potential, high current density, and high If / Ib value for methanol oxidation, which indicates that the CB[6]-Pt NPs exhibit excellent catalytic properties and good anti-poisoning abilities for methanol MORs. Then, the catalytic performances of CB[6]-Pd NPs for electrooxidation of formic acid were studied, which shows good electrocatalytic activities. These results further certified that CB[n]-M NPs (M= Pd, Pt) have excellent catalytic performances because the active sites on surface of these nanoparticles are fully exposed.5. An organic-inorganic hybrid compound which is composed of CB[6] and polyoxometalate (POMs) was prepared by using in-situ method. Supramolecules were formed via abundant hydrogen bonding interaction of organic and inorganic building blocks. Under visible light irradiation, the organic building block could act as a sensitizer and transfer electrons to the LUMO of POMs via the hydrogen bonding network, thereby, inducing the formation of radicals that are responsible for the degradation of dye molecules. As photocatalysts, CB[6]-POMs is superior to the POMs, owing to its utilization of visible light and insolubility in common solvents. Thess studies also show the great potential of CB[6] in environmental protection.更多还原