新穎金屬-有機架構物之特性鑑定及成長機制之研究

Structural Characterization and Growth Mechanism of Novel Metal-organic Frameworks

張朝順(Chao-Shuen Chang)

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)

https://doi.org/10.6838/YZU.2009.00333

摘要

由於全球暖化及地球石油儲藏量即將告竭，世界各研究單位正在積極開發新型乾淨之氫能源，以代替石化燃料，但因儲存的問題，使得氫氣的應用性受到相當大的限制。金屬有機架構物(MOFs)是將無機金屬與有機配基搭配鍵結而成的多孔性化合物，具有低密度、高熱穩定性、高比表面積等特性，故具有高氫氣儲存的潛力。因此，本研究之主要目的乃探討MOFs之合成方法、微細結構特性鑑定及其儲氫量之大小，亦藉由XRD、FE-SEM/EDS、TEM、BET、TGA、ESCA或XANES/EXAFS等貴重儀器來進一步的分析確認其成長過程及機制。
實驗部份主要包括利用不同的金屬(Al、Ni或Cr)硝酸鹽類作為合成原料，提供金屬配位中心，並可以連接不同之有機配基；合成反應溫度範圍在120~210℃，於不同的溶劑狀態下反應。所合成之MOFs共六種，分別為MIL-96-Al、MIL-96-In、MIL-96-Ga、MIL-100-Cr、MIL-100-Fe及Ni(HBTC)(4,4’-bipy)•3DMF。由FE-SEM分析結果顯示，MIL-96-Al、MIL-96-In、MIL-96-Ga隨著不同的合成方式，而出現不同的構形，大多以六角型或六角柱為主，且隨著反應物濃度變化，具有不同結晶形狀，分別具有7~20、1~15及20~225 μm的大小；但MIL-100-Cr和MIL-100-Fe的結晶較小，大約為200~600 nm；Ni(HBTC)(4,4’-bipy)•3DMF大小約4~20 μm。最初合成之產物會因含有不純物而不具孔洞性，為了使其產生孔洞性及高比表面積，必須經過高溫煅燒或溶劑清洗之處理程序，以清除孔洞中之有機物雜質而形成孔洞。經過上述處理之MIL-96-Al、MIL-100-Cr、MIL-100-Fe及Ni(HBTC)(4,4’-bipy)•3DMF，可測量出其比表面積分別為782、1960、1400及1155 m2/g；並由吸脫附曲線可知MOFs大多為Types Ι和ΙV，表示孔洞直徑為中孔和微孔的分布。XRD圖譜亦表示MOFs經過化學處理後具有良好之結晶性；EDS分析指出，MOFs成分中含有C、O以及不同金屬的成份；FTIR光譜得知MOFs於波長1400~1700 cm-1之C-O官能基，而在1866~1933 cm-1處會具有一微小波峰，為1,3,5三取代苯基之官能基，及因為水氣造成3000~3500 cm-1處，而有譜線加寬之現象；由TGA分析結果顯示MOFs具有較一般之有機化合物優異之熱穩定性，並可達到200~400℃。此外，亦利用X光吸收邊緣結構光譜(XANES)及延伸X光吸收細微結構光譜(EXAFS)，來進一步分析MIL-96-In的精細結構，由XANES分析指出MIL-96-In主要為In(III)的成份；EXAFS數據結果顯示MIL-96-In第一層之In-O鍵結之鍵長為2.13 Å，配位數為2。另以高壓熱重分析儀測量MIL-100-Cr、MIL-100-Fe及Ni(HBTC)(4,4’-bipy)•3DMF在室溫及450 psig下儲氫量分別為0.36 、0.11和0.08 wt%。

關鍵字

金屬-有機架構物 ； MILs ； 儲氫量 ； 高比表面積 ； 成長機制 ； 孔洞材料 ； 燃料電池

並列摘要

Both from the point of view of global warming and from that of the inevitable exhaustion of Earth’s oil reserve, worldwide interest is focused on using a clean burning substitute such as hydrogen in place of fossil fuels. However the storage of hydrogen is one of the most important challenges impeding its practical application. Metal–organic frameworks (MOFs) are a new emerging class of crystalline porous materials, displaying very low density, significant thermal stability and very high surface area. They offer significant opportunities for hydrogen storage. Therefore, the main objectives of present study were to develop and investigate the synthesis methods, fine structural characterization, and capacity of hydrogen storage of MOFs using XRD, FE-SEM/EDS, TEM, BET, TGA, ESCA, and XANES/EXAFS techniques.
Experimentally, MOFs were synthesized with different metal nitrates and in the presence of different solvents combined with different organic linkers, with the reaction temperatures range from 120 to 210℃. These MOFs were named as MIL-96-Al, MIL-96-In, MIL-96-Ga, MIL-100-Cr, MIL-100-Fe, and Ni(HBTC)(4,4’-bipy)•3DMF. The shapes of MIL-96-Al, MIL-96-In, and MIL-96-Ga were hexagon or hexagonal pillar with different reactant concentrations and the particle sizes were 7~20, 1~15, and 20~225 μm, respectively using FE-SEM. MIL-100-Cr and MIL-100-Fe had smaller crystal particles around 200~600 nm. Ni(HBTC)(4,4’-bipy)•3DMF had particle sizes were around 4~20 μm. Since as-synthesized MOFs having many impurities, it may cause low porosity. Therefore the cleaning methods, such as higher calcination temperatures or washing several times with different solvents at warm temperatures, were effective and approved to improve higher specific surface area and porosity. The specific surface area of MIL-96-Al, MIL-100-Cr, MIL-100-Fe, and Ni(HBTC)(4,4’-bipy)•3DMF were 595, 1960, 1400, and 1155 m2/g, respectively. Isothermal adsorption/desorption curves of MOFs were types I and IV, the distribution of pore diameter curves revealed that MOFs were microporous and mesopores materials. The XRD patterns represented that MOFs had well crystallinity after chemical treatment. EDS data indicated that MOFs consist of C, O elements and different kinds of metals. FTIR spectra exhibited vibrational bands in the usual region of 1400~1700 cm-1 for the carboxylic function, 1866~1933 cm-1 for benzene-1,3,5-tricarboxylic acid and 3000~3500 cm-1 for OH- group of these MOFs. TGA curves showed that these MOFs were more stable around 200~400℃ than other organic compounds. XANES/EXAFS spectroscopy was performed to identify the fine structures of MIL-96-In. The XANES spectra indicated that the valence of MIL-96-In was In(III). The EXAFS data also revealed that MIL-96-In had a first shell of In-O bonding with bond distance of 2.13 Å, respectively. The coordination number of MIL-96-In was 2. The hydrogen storage capacity of MIL-100(Cr), MIL-100(Fe), and Ni(HBTC)(4,4’-bipy)•3DMF were 0.36, 0.11, and 0.08 wt% at 450 psig and room temperature by using high-pressure thermogravimetric analysis.

並列關鍵字

Metal-organic Framework ； MILs ； Capacity of Hydrogen Storage ； High Specific Surface Area ； Growth Mechanism ； Porous Material ； Fuel Cell

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