金屬有機骨架:金屬、配位基種類於萃取多環芳香烴之影響

Metal-Organic Frameworks: the Effect of the Types of Metal and Ligand on the Extraction of Polycyclic Aromatic Hydrocarbons

蕭舒映(Shu-Ying Hsiao)

指導教授 ： 黃悉雅

中原大學/理學院/化學研究所/碩士(2016年)

https://doi.org/10.6840/cycu201600367

摘要

本論文探討以金屬有機骨架(metal-organic frameworks, MOFs)材料，製備金屬有機骨架-高分子(MOF-polymer)管柱，作為固相微萃取(solid phase microextraction, SPME)之吸附劑，進行9種多環芳香烴(polycyclic aromatic hydrocarbons, PAHs)萃取，探討MOF之配位基及金屬種類對於萃取之效果。
　　第一部分研究，比較不同配位基1,4-benzenedicarboxylate (BDC)、4, 4'-biphenyldicarboxylate (BPDC)及2,6-naphthalenedicarboxylate (2,6-NDC)所合成之MOF。實驗首先以BDC合成的MOF，MIL-101-(Cr)及MIL-53-(Al)，進行PAHs之萃取，由於PAHs結構是由二個或以上芳香環相互鍵結形成之碳氫化合物，可藉由MOF中配位基與PAHs間形成的π-π作用力達到吸附目的。結果顯示MIL-101-(Cr) 與MIL-53-(Al)對PAHs的萃取回收率分別為23.61%~66.87%與56.32%~78.84%，推測BDC結構為單苯環，因此π-π作用力較弱，但MIL-53-(Al)具呼吸效應，能有效增益對PAHs之吸附，而有較好的回收率。
　　以BPDC、2,6-NDC合成的MOF，DUT-5及DUT-4，對PAHs之萃取回收率分別為21.53%~69.35%及25.51~70.93%，說明具雙苯環結構的MOF相較於MIL-101-(Cr)有較好的萃取能力，此外，由於DUT-5之雙苯環配位基(BPDC)為單鍵可旋轉之結構，導致PAHs在吸附過程可能因DUT-5配位基之雙苯環間單鍵旋轉而不共平面，較不容易產生π-π作用力，造成吸附效果不佳。而DUT-4配位基為共平面之雙苯環結構，有利於PAHs以平面的方式進行吸附，產生較強之π-π作用力故得更好之吸附效果。
　　第二部分研究，為以相同配位基1,4-naphthalenedicarboxylate (1,4-NDC)，但不同金屬來源所合成一系列構型相同之1,4-NDC系列的MOF，討論不同金屬之MOF對於PAHs萃取之差異，分成不同過渡金屬元素及不同硼族金屬元素作比較。在所測試過渡金屬元素(Ｖ、Cr、Fe)中，依據原子半徑大小排列V為最大，Cr次之，Fe為最小，對PAHs之萃取回收率分別為，60.56%~100.05%、28.31~95.14%及19.39%~89.28%，說明當金屬原子半徑越大回收率越好，所建構的孔洞也相對較大，較有利於9種PAHs進入孔洞中，與配位基上的雙苯環形成更有利的π-π作用力，且藉由理論計算了解PAHs在不同過渡金屬元素之MOFs中之吸附行為，計算後的吸附能量趨勢能符合實際萃取中的回收率結果，搭配電子密度圖對於MOF吸附PAHs前後之變化，成功發現吸附PAHs後，金屬V電子密度改變最為明顯Cr次之，Fe為最小。
　　以不同硼族金屬元素(Al、Ga、In)討論，依據原子半徑大小排列In為最大，Ga次之，Al為最小，對PAHs之萃取回收率分別為，16.78%~76.85%、23.15~79.81%及61.82%~78.11%，說明當金屬原子半徑越大所建構的孔洞也相對較大，較有利於大尺寸(五環)PAHs進入孔洞中，與配位基上的雙苯環形成更有利的π-π作用力，並發現當中心金屬的電子親和力越大時(Al > Ga > In)，可大幅度的提升前六個尺寸小的PAHs回收率，藉由理論計算了解PAHs在不同硼族元素之MOFs中之吸附行為，計算後的吸附能量趨勢也符合實際萃取中的回收率結果，搭配電子密度圖對於MOF吸附PAHs前後之變化，成功發現吸附PAHs後，金屬Al電子密度改變最為明顯Ga次之，In為最小。

關鍵字

金屬有機骨架 ； 多環芳香烴 ； 配位基效應 ； 金屬效應 ； 萃取

並列摘要

In this study, metal organic frameworks-polymer (MOF-polymer) columns, which were synthesized with metal-organic frameworks (MOFs) materials and used as adsorbent in solid-phase microextraction of nine polycyclic aomatic hydrocarbons (PAHs). The extraction of PAHs was investigated based on the effect of ligand and metal types.
For the first part of the study, the MOFs were synthesized with different ligands, 1,4-benzenedicarboxylate (BDC), 4,4'-biphenyldicarboxylate (BPDC) and 2,6-naphthalenedicarboxylate (2,6-NDC), were discussed. Firstly, the PAHs were extracted using BDC-based MOFs, MIL-101- (Cr) and MIL-53- (Al). Due to the structure of PAHs, which composed of two or more aromatic hydrocarbon rings, the adsorption is based on the π-π interactions between the ligand of MOFs and PAHs. The results showed that the extraction recoveries of PAHs for MIL-101- (Cr) and MIL-53-(Al) are in the range of 23.61-66.87% and 78.84-56.32%, respectively. It suggests that the BDC structure is a monocyclic benzene ring. Therefore, the π-π interaction is rather weak whereas the breathing effect of MIL-53-(Al) can effectively enhance the adsorption ability of PAHs with extraction higher recoveries. Meanwhile, the extraction recoveries of PAHs were in the range of 21.53-69.35% and 25.51 - 70.93% for the MOF synthesized with BPDC (DUT-5) and 2,6-NDC (DUT-4), respectively. The MOFs with bicyclic benzene ring structure demonstrated better extraction efficiency compared to that of the MIL-101-(Cr). Furthermore, due to the rotatable single bond structure of bicyclic benzene ring ligand (BPDC) of DUT-5, the rotation occurs at non-co-plannar position causing its difficulty to form a π-π interaction during the adsorption process. In contrast, the ligand of DUT-4, which is co-planar bicyclic benzene ring structure, favors the adsorption at co-planar position to form a stronger π-π interaction, which improves the adsorption efficiency.
The second part of the study involve several MOFs, which were built using the same ligand, 1,4-naphthalenedicarboxylate (1,4-NDC), but with different central metal were utilized to extract PAHs. Transition metal elements and Boron group elements were separately compared. For transition metal elements (V, Cr, Fe), in which the largest atomic radius is V followed by Cr and Fe as the smallest, the extraction recoveries of PAHs were in the range of 60.56-100.05%, 28.31-95.14% and 19.39-89.28%, respectively. The results showed that better recoveries could be obtained when larger atomic radius is utilized. Besides, the constructed pore sizes are relatively larger, which favors the nine PAHs to pass through the pore of MOFs and form a stronger π-π interaction between the bicyclic benzene ring and the PAHs. Based on theoretical calculation, the adsorption behavior of PAHs with different transition metal element of MOFs showed similar trends of adsorption energy and matched with the results of actual extraction recoveries. Furthermore, the change of electron density maps of MOFs before and after PAHs extraction showed that the electron density of V demonstrated an obvious change followed by Cr and Fe. Different boron metal elements (Al, Ga, In), which were discussed based on the size of the atomic radius in which the largest was In followed by Ga and Al as the smallest, showed that extraction recoveries of PAHs were in the range of 16.78-76.85%, 23.15-79.81% and 61.82-78.11%, respectively. The results depict that the greater the metal atom radius the larger the constructed pore size, thereby favoring the nine PAHs to pass through the pore and form a stronger π-π interaction with the ligand. Furthermore, we found that the small size six PAHs recoveries could largely be enhanced when the central metal has greater electron affinity (Al> Ga> In). Based on theoretical calculation, we found that the adsorption behavior of PAHs with different transition metal element of MOFs afforded similar results with that of the adsorption energy after calculation and matched with the actual extraction recoveries. Furthermore, the change of electron density maps of MOFs before and after PAHs extractions showed an obvious change for Al followed by Ga and In.

並列關鍵字

Metal-Organic Frameworks ； Polycyclic Aromatic Hydrocarbons

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