層狀水滑石之合成與對二氧化碳吸附之研究

Abstract

本實驗利用共沈法合成不同比例的M(II)-Al-CO3 層狀水滑石(LDH)，其中M(II) = Mg、Ca、Sr、Ba。接著利用X光繞射儀(XRD)與傅立葉紅外光譜儀(FT-IR)進行結構鑑定。經由不同合成溫度的水熱法處理層狀水滑石後，可以獲得不同的顆粒大小，藉由掃描式電子顯微鏡(SEM)可以觀察到顆粒分佈大小隨著合成溫度的提高而變大。LDH的結晶特性利用高解析度穿透式電子顯微鏡(HRTEM)觀察。燒結溫度會改變LDH的結構而形成非晶相金屬氧化物，因此結構坍塌後會造成比表面積與孔隙度的不同，利用氮氣等溫吸附(BET)可以測量在400oC時，Ca-Al-CO3 3:1 LDH具有最大的孔隙度。熱重分析儀(TGA)在此被用來量測二氧化碳的吸附行為，在200-600oC的溫度範圍內進行吸附，以Ca-Al-CO3 Ca/Al = 3:1 LDH具有最佳的二氧化碳吸附能力，而Ca-Al-CO3 Ca/Al = 1:1 LDH則具有較好的吸/脫附迴圈的可逆性。 本實驗進ㄧ步利用spin coating方式製備層狀水滑石薄膜於陽極氧化鋁基板(AAO)上，以0.5 wt% PVA增強其鍵結力，利用XRD、SEM鑑定其結構與表面形貌，最後進行TGA二氧化碳吸附的測試，由於LDH之特性其薄膜應用在中高溫合成氣體淨化程序中二氧化碳捕集/分離上將扮演重要的角色。

M(II)-Al-CO3 layered double hydroxides (LDHs) with different M(II)/Al ratio was synthesized by coprecipitation in this study (where M(II) = Mg, Ca, Sr, and Ba). Its structure characterization and thermal evolution was investigated using X-ray diffraction (XRD) and FT-IR spectroscopy. In this work, the monodispersed layered double hydroxide with different morphologies including spherical nanoparticles and nanosheets were synthesized by hydrothermal method, where the scanning electron microscopy (SEM) images show that the particle size was larger by increasing annealing temperature. The crystallinity of LDH was investigated by high-resolution transmission electron microscope (HRTEM). Nitrogen adsorption isotherm (BET) have been applied to study the surface area and pore volume, which shows Ca-Al-CO3 3:1 LDH at 400oC with the largest pore size because of phase transformation to yield amorphous Ca-Al metal oxides. Thermogravimetric analysis (TGA) was used to analyze CO2 sorption from 200 to 600oC and Ca-Al-CO3 Ca/Al = 3:1 LDH revealed a highest CO2 adsorption capacity. Ca-Al-CO3 Ca/Al = 1:1 LDH have a better reversibility of adsorption/desorption cycles. Uniform thin film of layered double hydroxide on anodic alumina oxide (AAO) template was further formed by direct spin coating process using a homogeneous suspension containing monodispersed Ca-Al LDH. Also the structure characterization, morphologies, and CO2 adsorption will be discussed in this work. The LDHs unique properties for membrane can be particularly for application in high temperature CO2 separation and hydrogen production.