金屬有機架構物儲氫材料之合成及鑑定

Synthesis and Characterization of Metal Organic Frameworks for Hydrogen Storage

歐里(Abhijit Krishna Adhikari)

指導教授 ： 林錕松

元智大學/工程學院/化學工程與材料科學學系/碩士(2009年)

摘要

氫是一種乾淨的能量來源，並且不會產生任何的污染。對於氫的使用上，儲存氫氣是相當重要的課題。近年來，微孔有機金屬之架構(MOFs)，共價
組成擁有高孔隙度組成並由強金屬-氧-碳鍵結合在一起，且擁有相當大的表面積、熱穩定度和高儲氫程度特性。更深一層來說，氫氣吸附之能力與微孔
結晶材料的表面積有密切的關係。另外，能源的產生，會釋放大量CO2，進而改變天候狀況，為此，CO2 的捕獲和儲存即變的相當重要。然而MOFs 顯示對CO2 也會有好的吸附能力。好的吸附能力，主要取決於MOFs表面積和MOFs 中吸附的分子與金屬簇的交互反應。因此，本論文之主要研究目的為製備新的MOFs 方法及儲氫能力測試，以利作為後續儲氫的優質材料。MOFs 的結構特性並進一步由XRD、SEM、TEM、 BET、 TGA、 ESCA、 EPR 和 XANES/EXAFS 等技術作測試。
在實驗中，利用不同的金屬結合不同的化合物在不同的溶劑中合成。由FE-SEM可知不同粒徑大小的MOFs，MIL-47、 MIL-100、 MIL-101、MIL-102 和MOF-177，尺寸分別為2~15、 1~3、 1~5、10~15 及 2~5 μm。從先前製備之MOFs 包含了很多不純物，將會導致較低的孔隙度，為了改善表面積及孔隙度，將使用高溫煅燒方法處理。MOFs 比起其他材料在275~400℃擁有很好的熱穩定性。使用XANES/EXAFS spectroscopy 可測試出MOFs 精細結構及配位關係。XANES spectra 顯示出釩離子在MIL-47 中之價數為V(III)，鉻的價數在MIL-100、MIL-101 和 MIL-102 中為Cr(III)。EXAFS 的數據顯示出MIL-47 有第一個V−O 鍵結在1.8467 和 1.9761 Å，MIL-100、MIL-101 和MIL-102 有Cr−O 鍵結在2.1949、 2.1934 和 2.1956 Å。

關鍵字

金屬有機架構物，氫氣儲存，多孔洞性物質，MIL-47，MIL-100， MIL-101， MIL-102

並列摘要

Hydrogen is a clean power source, it provides energy without producing any pollutions. For the utilization of hydrogen, hydrogen storage technology is quite important. Recently, microporous metal-organic frameworks (MOFs), the crystalline compounds, so called inorganic-organic covalent compound has shown highly porous frameworks held together by strong metal–oxygen–carbon bonds and with exceptionally large surface area, thermal stability, and high capacity for hydrogen storage. Furthermore, the hydrogen uptake is correlated with the specific surface area for crystalline microporous materials. On the other hand, initiated by climate change concerns and the need to reduce CO2 (greenhouse gas) emissions by the power industries. CO2 capture and storage is very important issue due to environment safety. Recently, MOFs showed their good adsorption capacity for CO2 also. The adsorption capacity greatly depends on the surface area, the interactions between adsorbed molecule and the metal clusters of the MOFs. Therefore, the main objective of the present study is to develop new synthetic routes for MOFs as hydrogen storage materials. The fine structural characterization of MOFs has been performed by XRD, FE-SEM, TEM, BET, TGA, ESCA, EPR and XANES/EXAFS technique.
Experimentally, MOFs were synthesized with different metal clusters combined with different organic linkers into different solvents. The particle size of these MOFs named MIL-47, MIL-100, MIL-101, MIL-102 (MIL stands for Material of the Lavoisier Institute) and MOF-177 were 2~15, 1~3, 1~5, 10~15 and 2~5 μm, respectively revealed by FE-SEM micrographs. Since as-synthesized MOFs contain many impurities that may cause low porosity, to improve the specific surface area and porosity the samples were calcined at high temperature. The MOFs were thermally well stable around 275~400oC than other organic compounds. XANES/EXAFS spectroscopy was performed to identify the fine structures of MOFs. The XANES spectra indicated that the valency of Vanadium ion in MIL-47 was VIII, and the valency of chromium was CrIII in MIL-100, MIL-101 and MIL-102. The EXAFS data also revealed that MIL-47 had first shell of V−O bonding with 1.8467 and 1.9761 Å and MIL-100, MIL-101 and MIL-102 had Cr−O first shell with 2.1949, 2.1934 and 2.1956 Å respectively.

並列關鍵字

Metal-organic Framework, Hydrogen Storage, Porous material, MIL-47, MIL-100, MIL-101, MIL-102.

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