混合金屬沸石咪唑骨架薄膜合成、分析與應用於氫氣/二氧化碳的分離之研究

Abstract

在本研究中，提出了利用添加了第二種金屬元素進入沸石咪唑骨架中，形成混合金屬沸石咪唑骨架薄膜應用於氫氣與二氧化碳之氣體分離。第一部分為利用二次生長方式進行薄膜的生長，必須製備出奈米等級之粒子用於塗佈於基板上，以取代原位生長的成核階段。本研究利用調控溶液中鹼液之比例，接著以XRD和FTIR驗證其特徵結構及鍵結，再利用氮氣等溫吸脫附測量其比表面積、孔體積及孔洞大小，最後搭配SEM觀察表面形貌和微結構。由硝酸鋅(ZIF-8)和硝酸鈷(ZIF-67)並加入鹼液三乙胺即可室溫合成出混合金屬沸石咪唑骨架(ZIF-8-67)，隨著三乙胺莫耳濃度的增加，比表面積顯著的提高，並且從表面形貌可以觀察晶體顆粒隨之減小，竟而達到晶體顆粒約為100nm左右之粉體，已利於均勻緻密塗佈於基板上。第二部分為利用微波水熱法進行二次生長成功合成出混合金屬沸石咪唑薄膜(ZIF-8-67)，合成之二次生長水溶液利用UV-Vis鑑定鈷離子配位為四配位，並且調控配位鍵與鹼液濃度搭配XRD和SEM觀察薄膜生長最優化條件，最後以GPA測試混合金屬沸石咪唑骨架薄膜氣體分離特性。由於成功的將鋅金屬及鈷金屬引入沸石咪唑骨架結構中，其鈷金屬對於二氧化碳氣體具有較強作用力，故其在氣體分離試驗中呈現較低的二氧化碳穿透能力，增加了氫氣/二氧化碳分離率。同時由於結構中亦含有鋅金屬，因此在氣體分離變溫測試呈現相當穩定，並可以保持一定的分離率。

In this study, we proposed that the impregnation of two metal ions in the node of structure of ZIF, formation of mixed metal ZIF is applied to gas separation for hydrogen and carbon dioxide. In the first part, we prepare the nanoparticles for coating on the substrate to act as the nuclei for the secondary growth. The ZIF structures have been characterized by XRD and FTIR. The surface area was determined by N2 adsorption-desorption isotherms and SEM was used to observe the surface morphology and microstructure. The ZIF-8-67 containing both zinc ions (ZIF-8) and cobalt ions (ZIF-67) were synthesized at room temperature under triethylamine (TEA) base aqueous conditions. With increasing mole concentration of triethylamine, the surface area increased significantly, and the particles size obviously decreased. The nanoparticles (100nm) can be uniformly and densely coated on the substrate support for subsequent film growth. In the second stage, the hybrid mixed metal ZIF-8-67 membrane was synthesized on the nanoparticle-seeded substrate by microwave hydrothermal method. We used the UV-Vis to identify cobalt ion in the tetrahedral coordination and changed the mole ratio of the ligand and base to optimize the membrane structure and morphology by XRD and SEM. Finally, the gas separation property of hybrid mixed metal ZIF-8-67 membrane was determined by GPA. This study has successfully introduced zinc ion and cobalt ion into the zeolitic imidazolate framework structure where cobalt has a strong interaction for the carbon dioxide. Therefore, the gas separation test displays lower permeation for carbon dioxide but higher hydrogen/ carbon dioxide separation factor. The permeation of ZIF-8-67 membrane was also examined at different temperatures and demonstrated the stable gas separation factor.