Formation Mechanism of Secondary Building Units and Process-Structure-Property Relationships of Metal-Organic Frameworks: The Reproducibility Study of UiO-66 and In-MIL-68

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题名:	Formation Mechanism of Secondary Building Units and Process-Structure-Property Relationships of Metal-Organic Frameworks: The Reproducibility Study of UiO-66 and In-MIL-68
作者:	張芸瑄;Chang,Yun-Hsuan
贡献者:	化學工程與材料工程學系
关键词:	金屬有機結構材料;其次級結構單元;UiO-66;In-MIL-68;高壓反應器合成法;水熱合成法;不同的反應物添加速率;metal-organic frameworks;secondary building units;UiO-66;In-MIL-68;autoclave synthesis;solvothermal synthesis;cubic addition method
日期:	2016-06-16
上传时间:	2016-10-13 12:38:45 (UTC+8)
出版者:	國立中央大學
摘要:	金屬有機結構材料(MOF)，又稱多孔洞配位聚合物，其複雜的網狀結構及優異的性質吸引了許多注意。透過高壓反應器及水熱合成法是一種文獻中最常見的合成方法，其產物約為毫克規模。透過放大合成規模及不同的添加方法，金屬有機架構材料的再現性並未被仔細探討。因此，此篇研究的重點在透過不同尺度(毫克至克規模)的合成及不同種的合成添加方法來探討其在性質上的影響，進而預測其次級結構單元(SBUs)的形成及性質的再現性。在這篇論文裡我們將討論兩種MOF，UiO-66及In-MIL-68，及透過四種不同的合成添加方法來合成。不同的合成方法會影響MOF之SBUs的形成機制，進而影響SBUs的形成速率及MOF的成核速率。方法一的高壓反應器會使溶解度增加，進而降低反應器內的超飽和濃度，再加上反應並沒有攪拌，因此晶體的成核速率下降且成核數量少，故合成出來的UiO-66有最佳的結晶度、最大的顆粒大小、最高的比表面積，且配位基與金屬之間有較完整的鍵節數量。方法二是在大氣壓下進行合成，容器內的濃度與方法一相同。但大氣壓下的溶解度較低，因此方法二的超飽和濃度較方法一高，且反應有攪拌使晶體的成核速率快，故此方法合成出來的UiO-66結晶度差且晶體顆粒小，從TGA檢測可以得知有機配位基與金屬基團之間鍵結上的缺陷會使比表面積下降。而方法三、四的反應條件與方法二相似，唯一的差別是反應物的添加速率。在反應一開始時，緩慢添加反應物會使濃度降低，但溶解度與方法二同，故超飽和濃度會降低並限制金屬有機結構材料的成核速率並使晶體有序的成長，因此其性質會介於方法一、二之間。此外，方法一、三、四合成出來的UiO-66其光致發光波長皆接近320nm，相對於方法二則是385nm，此結果也可以從XPS的C1s圖譜的束縛能得到呼應。但對於另一種金屬有機結構材料In-MIL-68，不同的合成方法並不太會影響到其性質，因此不同合成方法得到的In-MIL-68有相似的結晶度、化學鍵結、有機配位基數量、光致發光波長、比表面積及原子束縛能。在In-MIL-68唯一的差異僅是顆粒大小，方法一的低成核速率會降低成核數目，使產物的顆粒最大約100μm，但因為合成沒有攪拌而顆粒大小分布較廣。方法三的成核速率快而成長速率慢，因此其顆粒大小最小約5μm。我們可以由以上的實驗結果得知，UiO-66的次級結構單元的形成機制及步驟較複雜，故UiO-66是一種對製程敏感的金屬有機架構材料，其物理性質會受到不同的合成方法影響；而In-MIL-68的次級結構單元形成機制相對簡單，其性質對不同的製程方法不敏感，擁有較佳的性質再現性。;Metal-organic frameworks (MOFs), also known as porous coordination polymers, have attracted tremendous interests due to its complicated structures and outstanding properties. The solvothermal synthetic method without stirring in an autoclave was most commonly used for the milligram scale synthesis. The reproducibility of MOFs’ properties under the different scale and addition rate have been overlooked. Therefore, the aim of this thesis was to understand the reproducibility of MOFs from different scale and synthetic methods. In this thesis, two well-known MOFs, UiO-66 and In-MIL-68 were taken into account, and four kinds of synthetic methods were fully investigated. The different synthetic methods would affect the formation mechanism of MOF’s secondary building units (SBUs), hence altering the formation rate of SBUs and nucleation rate of MOFs. Mode I was synthesized in an autoclave with no agitation and under high pressure. Therefore, the solubility of solutes was increased. However the concentration of solution did not change. The degree of supersaturation decreased. The nucleation rate was lower, and resulted in the larger crystal sizes and better crystallinity of MOF. Mode II was synthesized under the atmospheric pressure and with agitation. The concentration was the same as mode I but the solubility was lower than the one of mode I, it resulted in the higher degree of supersaturation than the one of mode I. Therefore, mode II had the higher nucleation rate, and gave the smaller crystal sizes, less crystallinity and more defects of MOF. Modes III and IV were similar to mode II, the only difference was the addition rate of ligand and precursor solution. In modes III and IV, the concentration for the added ligand and precursor were both lower than the one in mode II, but the solubility here was the same with mode II. Therefore, the degree of supersaturation for them were lower than the one of mode II. From the above results, we concluded that in UiO-66, mode I would produce the largest crystal size, crystallinity, surface area, and the coordination amount between ligands and Zr-based SBUs. Mode II would give the opposite results for UiO-66. Besides, the photoluminescence emission signals were similar for both modes I, III, and IV at around 320 nm while 385 nm for mode II, and those results also corresponded to the C1s core-level spectra from XPS. But for another kind of MOF, In-MIL-68, the properties such as crystallinity, chemical bonding, ligand amount, PL emission signal, surface area, and binding energy would not be affected too much by different synthetic processes. The only difference was shown in mode III for In-MIL-68 that cubic addition method would give the smaller crystal size at around 5 μm. As a result, we concluded that the physical properties of UiO-66 were process-dependent because the formation steps of SBUs were more complex. On the contrary, In-MIL-68 showed more uniform properties due to the simple formation mechanism of SBUs. Therefore, we concluded that In-MIL-68 was process-independent.
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