氧化鐵/鈀奈米觸媒之合成及於偶合反應之應用

Abstract

本篇論文主要是利用水熱法（hydrothermal method）合成之氧化鐵奈米環（iron oxide nanorings）當作載體，將具有高催化活性的鈀奈米粒子成長於其表面，形成氧化鐵/鈀複合奈米觸媒，並應用於鹵素芳香環碳-碳鍵偶合反應（homocoupling reaction）的催化。首先利用多巴胺（dopamine）分子的鄰位氫氧基與氧化鐵產生螯合作用（chelation）修飾氧化鐵表面，再利用其多巴胺分子外露的胺基來與鈀離子形成錯合物，進而將鈀離子吸附於氧化鐵奈米環表面，最後加入還原劑抗壞血酸（L-ascorbic acid）還原鈀離子，形成氧化鐵/鈀複合奈米觸媒，此製程完全在水溶液中進行，避免有機溶劑的使用，符合綠色化學的概念。我們利用穿透式電子顯微鏡（Transmission Electron Microscopy, TEM）檢測所形成奈米材料的形狀及大小，能量散射光譜儀（Energy Dispersive Spectrometer, EDX）與X光粉末繞射儀（X-ray Powder Diffractometer, XRD）來鑑定其組成與晶型，以及X射線光電子能譜儀（X-ray Photoelectron Spectroscopy, XPS）來分析其觸媒特性。 在觸媒催化偶合反應的部分，我們利用氫氧化四丁基銨（tetrabutylammonium hydroxide）當作相轉換試劑及抗壞血酸當作還原劑，在水溶液中對溴苯（bromobenzene）進行偶合反應，結果顯示產物聯苯（biphenyl）的產率高達86%，證明此氧化鐵/鈀複合奈米觸媒具備良好的催化性質，推測因具中空結構的鐵奈米環提供了高的表面積/體積比（surface-to-volume ratio）來成長高密度的鈀奈米粒子，同時載體本身亦幫助鈀奈米粒子保持分散特性，產生高催化產率；最後我們也利用氧化鐵的磁特性，輕易的對此複合奈米觸媒進行了快速分離、回收、再利用。因此我們相信此方法合成之異相觸媒於水溶液相進行催化偶合反應具有極高的應用潛力。

The thesis focused on developing facile synthetic approaches to fabricate highly efficient and reusable Fe3O4/Pd nanocatalysts and applying them in the homocoupling reaction of aryl halides. Firstly, Fe3O4 nanorings were synthesized by the hydrothermal method, which were used as a support for the growth of Pd nanoparticles. Then, via chelating on the Fe3O4 surface, the dopamine residual amine groups were used to assemble Pd4+ ions onto the surface. Finally, the addition of reducing agent (L-ascorbic acid) induced the growth of Pd nanoparticles onto the Fe3O4 surface leading to the gradual formation of composite nanocatalysts. Transmission electron microscope (TEM), energy dispersive spectrometer (EDX), X-ray powder diffractometer (XRD), and X-ray photoelectron spectrometer (XPS) were used to characterize the composition and structure of Fe3O4/Pd nanocatalysts. The catalytic efficiency of Fe3O4/Pd nanocatalysts for homocoupling reaction was tested in aqueous solution. In the presence of the phase transfer agent (tetrabutylammonium hydroxide), the yield of the product, biphenyl, was as high as 86%. The high catalytic performance could be due to a large surface-to-volume ratio provided by the Fe3O4 nanorings, which had the chance to grow denser but still well-dispersed Pd nanoparticles on Fe3O4 nanorings’ surface. The Fe3O4/Pd nanocatalysts were easily and rapidly separated and reused by applying a magnetic force. These attempts in synthesizing Fe3O4/Pd nanocatalysts and the application of coupling reaction were done with the central concepts of “green” and “sustainability”. We believe that the as-prepared Fe3O4/Pd nanocatalysts have great potential in organic coupling reactions in aqueous solution with high efficiency, recyclable ability while being less harmful towards our environment.