磁性纳米团簇表面贵金属纳米粒子的分散稳定机制和催化性能研究

There are many drawbacks such as complicated synthesis process, aggregation and deactivation of noble metal nanoparticles during the catalytic transformations for noble metal based magnetic nanocomposites. Therefore, one simple method will be developed to synthesize simultaneously functional polymers and noble metal nanoparticles on the surface of magnetic nanoclusters, with amphiphilic polymer as structure-directing agent, on the basis of the oxidation / reduction reaction between functional monomers and noble metal precursors. Confinement of dispersed highly noble metal nanoparticles within functional polymer structures, could endow nanocatalysts with excellent activity and high stability, resulting from chemical immobilization of polymer functional groups and migration-limited effect of polymer chains on metal nanoparticles. In other words, it will be achieved to establish dispersion mechanism of noble metal nanoparticles on the surface of magnetic nanoclusters. Meanwhile, the nucleation and growth rates of noble metal nanoparticles and functional polymers, determining the size, morphorlogy and distribution of noble metal nanoparticles into polymer, will be controlled by tuning reaction parameters such as the kind and ammount of amphiphilic polymer, the feed ratio of monomer and noble metal precursor, the polarity of solvents, temperature and so on. As well as stabilizing noble metal nanoparticles on the surface of magnetic nanoclusters, the key goal in this study is just to synthesize the novel magnetic nanocomposite catalysts with excellent activity and high stability via a facile method, to explore structure-activity relationship between nanocoposite catalysts and catalytic performance, and to lay the practical and theoretical foundation of further controllable synthesis and catalytic application of this kind of nanocomposite catalysts.

针对贵金属基磁性纳米复合材料存在合成过程相对复杂和催化过程中贵金属纳米粒子易于团聚、失活等问题，本项目提出以两亲性高分子为导向剂，借助功能聚合物单体和贵金属源之间的氧化还原作用，在磁性纳米团簇表面同步合成功能聚合物和贵金属纳米粒子的方法。利用聚合物链官能团的锚固作用和聚合物链缠绕的限域作用，使弥散分布于聚合物结构中的贵金属纳米粒子，在催化反应过程中保持其高分散性、高活性和高稳定性，从而建立磁性纳米团簇表面贵金属纳米粒子的分散稳定机制。同时，本项目通过改变两亲高分子种类、用量，单体与贵金属源的投料比，溶剂极性，反应温度等参数调控聚合物和贵金属纳米粒子的成核和生长速率，优化贵金属纳米粒子在聚合物结构中的尺寸、形态和分布，利用简单方法实现新型高效、稳定的磁性纳米复合催化材料的可控合成，并探究纳米复合材料与催化性能间的构效关系，为拓展此类复合材料的可控合成和催化应用提供实验基础和理论依据。

针对贵金属基磁性纳米复合材料存在合成过程相对复杂和催化过程中贵金属纳米粒子易于团聚、失活等问题，本项目以开发高效贵金属基磁性限域催化剂，建立磁性纳米团簇表面贵金属纳米粒子的限域稳定机制为目标，进行了深入研究。首先，基于导电聚合物单体和贵金属源之间的同步还原氧化还原反应，在四氧化三铁纳米团簇表面一步构建了导电聚合物和贵金属纳米粒子，合成了“核-卫星”结构Fe3O4@Ppy/Pd磁性空间限域催化剂和核壳结构Fe3O4@PEDOT/Pt/Pd双金属磁性空间限域催化剂，表现出良好活性和稳定性，简化了磁性限域催化剂的合成工艺，基于功能聚合物对贵金属纳米粒子的配位作用和缠绕限域作用，初步建立了磁性纳米团簇表面贵金属纳米粒子的限域稳定机制。其次，考虑到聚合物载体在催化过程中可能被强溶剂或强碱所破坏，从而降低磁性限域催化剂的稳定性，本项目进而提出将聚合物载体热解实现其热交联或者部分碳化，提升其耐溶剂和耐碱性。基于导电聚合物PEDOT和氨基酚醛树脂的热解过程，分别得到了“摇铃”结构Fe3O4@Void@Thermally crosslinked PEDOT/Pt磁性空间限域催化剂和 “摇铃”结构Fe3O4@Void@N-Carbon@Au@N-Carbon，进一步增强了磁性限域催化剂的稳定性，拓展了其应用范围。再次，将贵金属纳米粒子空间限域于载体中有利于增强其稳定性，却降低了反应底物与活性中心的碰撞几率，降低了其催化活性，本项目进而提出构建“摇铃”结构磁性空间限域催化剂，如“摇铃”结构Fe3O4@Void@P(4VP-DVB)/Au、Fe3O4@Void@Thermally crosslinked PEDOT/Pt、Fe3O4@Void@N-Carbon@Au@N-Carbon，“摇铃”型级次结构Fe@SiO2/Ni等磁性空间限域催化剂等，反应底物可通过中空壳层双向扩散向弥散分布于壳层结构中的金属纳米粒子，提高反应底物与催化活性位点的碰撞几率，从而增强其催化活性。这为磁性空间限域催化剂的可控合成和催化应用提供了实验基础和理论依据。