贵金属基核壳结构多功能复合纳米材料的构筑及其性能研究

The core-shell nanocomposites containing noble metal cores have been attracting much scientists' interest due to their broad applications in optics, electronics, magnetism, biology, sensing and catalysis. Though different strategies have been developed to fabricate these core-shell nanocomposites, most of the obtained shell materials are limited to several typical metal oxides, leading to few types of functionalities. As a result, the core-shell nanocomposites possess the limited capacity to tailor the properties of noble metal nanoparticles. Aimming at extending the types of the shells and improving their functionalities, this proposal suggests to design and fabricate the multifunctional nanocomposites containing noble-metal cores by controlling the nucleation and growth process of the shell materials in the solution. Such composites can realize the function synergy of varying materials in single nanostructure. In this proposal, the mechanism of heterogeneous nucleation and growth of the shells on the surface of noble metal nanoparticle cores will be studied in detail, and the interfacial structures between the cores and the shells will be disclosed. By using different types of characterization methods and density functional theory (DFT), the structural effect of the core-shell nanocomposites on their catalytic performance will be also explored. The results in this proposal are expected to benefit us understanding the relationship between the structure and catalytic activity of the core-shell nanocomposites.

贵金属基核壳结构纳米材料在光学、电学、磁学、生物、传感和催化等诸多方面具有广泛的应用价值，引起了科学家的广泛关注。虽然，文献报道了利用不同的策略构筑贵金属基核壳结构纳米材料，但是获得的壳层材料主要集中于几类典型的金属氧化物，种类较少，功能单一，对贵金属胶体粒子性能的调控能力有限。本项目拟以拓展壳层的种类和增强其功能性为出发点，通过调控溶液中壳层材料的成核和增长过程，构建以贵金属胶体粒子为核、复合金属氧化物和功能性金属-有机骨架材料为壳的核壳结构多功能复合纳米材料，实现不同类型材料的性能协同。本项目将重点探讨壳层材料在贵金属胶体粒子表面的异相成核和生长机理，阐明贵金属胶体粒子与壳层材料间界面的微观结构特征。借助于典型的催化反应体系，结合多种表征手段和密度泛函理论，揭示核壳型纳米材料的微观结构对其催化性能的调控规律。

本项目以研究典型催化反应为出发点，以贵金属基核壳结构纳米催化剂的设计和可控制备为突破口，系统研究了贵金属纳米粒子与金属氧化物以及金属-有机骨架材料（MOFs）间的异相成核和生长机理，并对其进行结构调控，从而实现贵金属纳米粒子与壳层间的功能协同。同时结合密度泛函数理论，阐明两者间的协同催化原理。研究成果可归结为3个方面：（1）利用壳层保护内核组分提高其稳定性。发展了一种简单通用的方法制备以贵金属纳米粒子（Au、Pt、Pd）为夹层和以金属氧化物（TiO2、ZrO2）为壳层的三明治空心结构，可以有效地防止纳米粒子的迁移和烧结，在催化CO氧化、光解水制氢以及硝基苯还原中展示出较好的活性和稳定性。（2）壳层与内核用于催化串联反应，且壳层孔道可限域底物分子，促进内核选择性催化特定官能团。采用双溶剂热法制备了以单一Pd纳米粒子为内核和以IRMOF-3为壳层的核壳结构催化剂，在以4-硝基苯甲醛和丙二腈为底物经串联催化反应（碱性IRMOF-3催化两者发生缩合反应，然后内核Pd催化选择性加氢）制备医药中间体2-（4-氨基亚苄基）丙二腈中展现出很好的活性、选择性和稳定性。（3）利用内核与壳层间的协同效应实现α，β-不饱和醛中热力学不优越的C=O双键选择性加氢。肉桂醛中含有共轭的C=C和C=O双键，热力学上易于C=C双键加氢，因而不利于医药中间体肉桂醇的生成。针对这一问题，设计和合成了以Pt纳米粒子为夹层和以MIL-101为壳层的三明治结构，利用壳层中配位不饱和金属位点Fe和Cr与肉桂醛中C=O双键接触并对其活化；同时Pt用于活化H2，实现了热力学不优越的C=O双键选择性加氢，大大提高了肉桂醇的收率。同时，引入不同MOFs作为壳层以及不同α，β-不饱和醛作为底物分子，都展现出了较好α，β-不饱和醇选择性。上述工作的开展可为新型多功能催化剂的设计和制备提供新思路，同时也可为具有重要工业应用和挑战性催化难题的解决提供重要借鉴。