Structural Evolution of Metal-Organic Frameworks - From Primary Crystals to Spherical Agglomerates

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题名:	Structural Evolution of Metal-Organic Frameworks - From Primary Crystals to Spherical Agglomerates
作者:	蔡宜蓁;Tsai,Yee-Chen
贡献者:	化學工程與材料工程學系
关键词:	動力學;金屬有機結構材料;球晶;Kinetics;Metal-Organic Frameworks;Spherical Agglomeration
日期:	2014-07-24
上传时间:	2014-10-15 14:37:21 (UTC+8)
出版者:	國立中央大學
摘要:	此篇論文展示了金屬有機結構材料[In(OH)bdc]n從分子合成到結晶，及聚集成球狀顆粒的結構演化。此材料於三種溫度下合成，並比較其產物的分子結構、化學鍵結、顆粒分佈、孔洞大小、吸附能力及感測特性，在結晶成長曲線中我們發現了在金屬有機結構材料中從未報導過的二次結晶，儘管三個溫度的結晶曲線皆擁有相似的第二階段結晶機制和二次結晶，但80oC第一階段中，擴散控制帶走非晶相分子，而導致在80oC合成的金屬有機結構材料擁有最佳的結晶度。在吸脫附曲線上，只有在60oC合成的金屬有機結構材料有明顯的遲滯現象，代表了同時存在的微孔及中孔結構，而80oC的材料因有著微孔結構和最佳的結晶度，所以擁有最高的吸附比表面積。另外在光激光感測上三種溫度合成的樣品皆展現了相同的吸附性質，由於合成參數僅影響產品顆粒大小分布、吸附行為及孔洞結構，不太影響材料結晶結構及氣體分子感測性質，有利於參數最佳化的調整。此結晶成長曲線可作為合成參數和最終產品性質的關係依據，搭配監控設備可達到於反應過程中調整參數以獲得所需產品性質。另一方面，金屬有機結構材料的球狀聚合在正庚烷/乙醇/聚乙二醇的系統中進行，且材料結晶結構不受樣品負載量影響。但較低的活化溫度(150oC)無法完全去除孔洞中的正庚烷分子，氣體吸附量大大降低，聚乙二醇的包覆更加降低其吸附量，但感測功能依然不變。大幅降低的卡爾指數代表其增加的粉體流動性，有利於未來填充、壓錠等製程。 ;The aim of this thesis was to show the structural evolution of [In(OH)bdc]n crystals from molecular synthesis to primary crystals, which then aggregated into spherical agglomerates. The synthesis of [In(OH)bdc]n crystals were conducted at three different temperatures 60o, 80o and 100oC. The crystal growth curves can be deduced by UV/vis spectroscopy. The crystallite structure, chemical bonding, agglomerate size distribution, pore size, adsorptive capability, and sensing characteristics were illustrated and compared among the products synthesized at three different temperatures. From the crystal growth curves, the secondary crystallization of MOFs was discovered which had not been reported before. The [In(OH)bdc]n crystals synthesized at 80oC were the best based on their superior adsorption surface areas and crystallinity. It was because the diffusion control taking place during the initial period of nucleation had removed the amorphous molecules and led to the best crystallinity. Only [In(OH)bdc]n crystals synthesized at 60oC showed clear hysteresis indicating the existence of both micro- and mesopores. The micropores and high crystallinity led to the highest adsorption surface area of [In(OH)bdc]n crystals synthesized at 80oC. The PL sensing characteristics were consistent between the three products synthesized at 60o, 80o and 100oC individually. The process-history independence of PL allowed [In(OH)bdc]n crystals to be synthesized in various conditions. The crystal growth curve can be served as a relationship between the synthetic parameters and the final product properties. Combined with the in situ monitoring instruments, we could control the conditions during synthesis and attained products with the desired properties. On the other hand, the spherical agglomeration of [In(OH)bdc]n crystals was carried out in a n-heptane/ethanol/PEG system. Different amounts of MOF crystals (i.e. 1g and 5g) were used to compare the effect of sample loading. After the agglomeration process, the structure of MOF crystals remained integrity. But the lower desolvation temperature at 150oC could not eliminate the trapped n-heptane entirely, which led to the reduction in the amount of N2 adsorbed. The micropores were covered by PEG which worsened the situation and the adsorption volume decreased to 3.5 cm3/g. Although the spherical agglomerates lost the gas storage capability, the PL sensing characteristics were still remained. The improvement of flowability was indicated from the reduction in the Carr’s index which would benefit the powder handling for sensor fabrication.
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