含缺陷鋯金屬有機框架之氣體吸附機制模擬計算探討;Computational Investigation of Gas Adsorption Mechanism in Defective Zirconium-Based Metal-Organic Frameworks

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題名:	含缺陷鋯金屬有機框架之氣體吸附機制模擬計算探討;Computational Investigation of Gas Adsorption Mechanism in Defective Zirconium-Based Metal-Organic Frameworks
作者:	黃鈞平;Huang, Chun-Ping
貢獻者:	化學工程與材料工程學系
關鍵詞:	缺陷鋯金屬有機框架;蒙地卡羅;氣體吸附機制;Defective zirconium-based metal-organic frameworks;Monte Carlo simulations;gas adsorption mechanism
日期:	2019-07-26
上傳時間:	2019-09-03 12:30:56 (UTC+8)
出版者:	國立中央大學
摘要:	UiO-66是一種孔洞材料其結構由鋯金屬離子簇和配位基(對苯二甲酸)所組成的鋯金屬有機框架結構，因為此鋯金屬有機框架結構具有出色的熱穩定性、化學穩定性，和較大孔洞體積所以是一直以來在氣體捕捉和分離的應用上是非常熱門的材料。因為在高缺陷程度的鋯金屬有機框架可以維持其穩定性所以適合用缺陷工程方法來調整不同的物理和化學特性。研究顯示在UiO-66製程中加入不同的改質劑(modulators)可以產生具有缺陷(missing-linker defect)的晶體結構，此缺陷和缺陷處的補償基團(defect compensating groups)的存在會改變孔洞性(porosity)、表面積(surface area)和氣體與MOF之間的作用力，進而改變其氣體吸附機制。有關於MOF的缺陷和配位基官能化改質的研究一直發展中，然而目前尚未發現有關於探討具有不同補償基團的缺陷UiO-66在不同壓力下是如何影響氣體吸附機制的決定因子和氣體分佈的變化，在此研究中我們使用蒙地卡羅法(Monte Carlo simulations)來進行二氧化碳和氮氣吸附並依照其結果來探討氣體在具有不同補償基團的缺陷UiO-66中的吸附機制，此外我們也探討不同補償基團對於氣體分離的影響。我們根據不同的compensated groups把缺陷UiO-66分成二類進行分析:鹵素官能基系列(Halogen groups series)和碳氫官能基系列(Hydrocarbon groups series)，結果顯示高壓下，二氧化碳在碳氫官能基缺陷模型中的氣體吸附量主導因素是自由體積分率(fractional free volume),而在鹵素官能基缺陷模型的高壓吸附中，自由體積分率(fractional free volume)和等溫吸附熱(isosteric heat)二者對於氣體吸附量都是重要的影響因素。高壓下的氮氣在碳氫官能基缺陷模型的吸附量主導因素是自由體積分率，在鹵素官能基缺陷模型吸附量的主導因素是表面積(surface area)，然而低壓下二氧化碳和氮氣在全部的缺陷模型中的吸附量的主導因素都是等溫吸附熱(isosteric heat)。在分析氣體分佈時我們根據配位基(BDC)的密度把缺陷模型內的吸附位置分成二類High BDC density (HBD) sites and low BDC density (LBD) sites,而對於二氧化碳和氮氧在缺陷模型的氣體分佈，大多數情況下HBD sites是主要吸附位置，除了在LBD位置具有大自由體積的模型例如channel models的高壓氮氧吸附以及在具有CF3官能基模型的低壓二氧化碳吸附會出現在LBD位置。 ;UiO-66 is kind of zirconium-based metal-organic frameworks (Zr-MOFs) which is consisted of zirconium metal cluster and benzene-1,4-dicarboxylic acid (BDC) as its ligands, and it is a popular material for gas adsorption and separation application due to its excellent chemical stability, thermal stability and large free volume. Zr-MOFs are candidate which are suitable to tune different physical and chemical properties by defect engineering because Zr-MOFs can retain stability at high defect concentration. Studies have shown that the missing-linker defect can be created in the UiO-66 crystal structure by adding different modulators in the synthesis step. The existence of defect and compensate groups at defect sites can change the porosity, surface and the interaction between gas and MOF lead the gas mechanism to change. There are many studies concerning defect and ligand functionality, however, we have not found the study concerning about compensating groups of defective UiO-66 affecting the dominant factor in adsorption mechanism and changing of adsorption distribution with varied pressure. In this study, we use Monte Carlo (MC) simulations to execute the CO2 and N2 adsorption and investigate the gas adsorption mechanism in defective UiO-66 with different compensating groups. In addition, we also investigated the influence of different compensating groups to defective UiO-66 be used for gas separation. We classified defective UiO-66 into two series to do analysis based on different compensating groups, one is hydrocarbon-series and the other is halogen-series. The results indicate that fractional free volume is key factor for CO2 uptakes in hydrocarbon-series defective models at high pressure, and both of fractional free volume (FFV) and isosteric heat are important factors for CO2 uptakes in halogen-series at high pressure. For N2 uptakes at high pressure, FFV is key factor for hydrocarbon-series defective models, and surface area is key factor for halogen-series defective models, however the isosteric heat is key factor for CO2 and N2 uptakes in all defective models at low pressure. We classified the adsorption sites into high BDC density (HBD) sites and low BDC density (LBD) sites based on the BDC ligands density, and in most instances the HBD sites is main adsorption sites for CO2 and N2 except N2 adsorption in channel models under high pressure and CO2 adsorption in TriF model under low pressure.
顯示於類別:	[化學工程與材料工程研究所] 博碩士論文

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