金屬有機骨架複合材吸附揮發性有機化合物之研究與軟性X-ray巨觀結構鑑定技術

Abstract

本論文主要使用金屬有機骨架(Metal-Organic Frameworks, MOFs)與高分子複合進行揮發性有機汙染物的吸附移除，其中探討了靜態和動態等不同種類的吸附方式，並以理論計算來模擬和佐證實驗結果。後面的部分展現一種新型態的穿透式軟性X-ray成像方式，來建構非均相材料在巨觀結構的實際構形。論文第一部分為了能符合工業化的需求，我們針對MIL-68(Al)的製備做了改良，與先前報導相比，選用了更為環境友善的異丙醇(IPA)作為合成的主要溶劑，同時藉由晶種的預添加，成功地將製程的產能擴大至原先的500倍，並且在三次的溶劑回收重複合成實驗中，也取得優異的成果，在X-ray繞射圖譜以及N2表面積孔徑分析儀的結果表明，放大製成的產品效能與小量製程的效能一致，甚至更為優異。針對新製備方式的MIL-68(Al)，示範了其對乙酸(AA) 吸附能力，即使在100 ppm 的低起始濃度下，也顯示出良好的AA 去除率(100% 去除率)，表現出比市售活性碳和沸石更好的吸附效能。論文的第二部分同樣進行VOCs的吸附實驗，首先將多種MOFs進行對氣相的甲苯氣體的吸附實驗，進一步將MOFs與聚乙烯醇(PVA)複合生成MOF@PVA的複合粒材，並製備了不同比例的 MOF@PVA 珠複合材料，找出孔隙率最佳的比例進行揮發性有機物的吸附測試。結果成功製備出10%、20%、30% PVA/MOF混摻比例的高分子顆粒，且10% MIL-68@PVA有著高達0.7 g/g的甲苯氣體吸附量，與市售活性碳和沸石吸附劑相比有著1.5~3倍的吸附優越性。而在低濃度的甲苯動態吸附測試結果中，10% HKUST-1@PVA顆粒卻有著比10% MIL-68@PVA顆粒更好的甲苯吸附效率，總吸附量接近3倍差距，並且透過動力學模型的模擬成功找出了較適合解釋在低濃度動態下微孔MOFs對甲苯的吸附機理，表明在高濃度甲苯環境如工廠中更適合以MIL-68@PVA顆粒作為吸附劑，而低濃度工業及家庭廢氣則更適合小孔徑的HKUST-1@PVA。論文的第三部分介紹了一種新型態巨觀結構的鑑定技術，利用軟X射線斷層掃描技術透過目視觀察不同激發能量在不同能帶中的相應圖像來檢查金屬有機骨架的多維結構，例如核殼和空心骨架，或是不同的金屬元素。結果表明，利用軟X射線斷層掃描（SXT）可以更為直觀的觀察結構中金屬的分佈，以及觀察MOFs所具有的中空孔類型。這項透過 SXT 對 MOF 進行的開創性評估顯示了多維金屬有機框架結構識別的出色性能。

This thesis primarily explores the adsorption and removal of Volatile organic compounds (VOCs) using Metal-Organic Frameworks (MOFs) in conjunction with polymer composites. It investigates different adsorption methods, including static and dynamic, and employs theoretical calculations to simulate and corroborate experimental results. The latter part presents a novel form of transmission soft X-ray imaging technique to construct the actual configuration of heterogeneous materials at a macroscopic scale.The first part of the thesis focuses on the enhancement of MIL-68(Al) synthesis to meet industrial demands. Compared to previous reports, a more environmentally friendly solvent, isopropanol (IPA), was utilized in the synthesis. Additionally, by pre-adding seed crystals, the production capacity was successfully increased by 500 times. Excellent results were achieved in three cycles of solvent recovery and repeat synthesis experiments, as evidenced by X-ray diffraction patterns and N2 surface pore size distribution analysis, indicating consistent or even superior performance of the upscaled product compared to small-scale synthesis. Demonstrations of the adsorption capacity of the newly prepared MIL-68(Al) for acetic acid (AA) showed remarkable removal efficiency (100% removal rate) even at low initial concentrations of 100 ppm, outperforming commercially available activated carbon and zeolite in adsorption efficiency.The second part of the thesis also conducted adsorption experiments of VOCs. Various MOFs were first tested for the adsorption of toluene gas in the vapor phase. Subsequently, MOFs were combined with polyvinyl alcohol (PVA) to form composite beads (MOF@PVA), and different ratios of MOF@PVA composite beads were prepared to determine the optimal pore volume for adsorption of volatile organic compounds. Results showed successful preparation of polymer beads with 10%, 20%, and 30% PVA/MOF hybrid ratios, with 10% MIL-68@PVA exhibiting a high toluene gas adsorption capacity of up to 0.7 g/g, representing 1.5 to 3 times higher adsorption superiority compared to commercially available activated carbon and zeolite adsorbents. Interestingly, in dynamic adsorption tests at low toluene concentrations, 10% HKUST-1@PVA beads exhibited better toluene adsorption efficiency than 10% MIL-68@PVA beads, with nearly a 3-fold difference in total adsorption, and the simulation of kinetic models successfully identified a mechanism better suited to explain the adsorption of toluene by microporous MOFs at low concentrations, indicating that MIL-68@PVA beads are more suitable as adsorbents in environments with high toluene concentrations such as factories, while HKUST-1@PVA with smaller pore size is more suitable for industrial and household waste gases with low concentrations.The third part of the thesis introduces a novel technique for identifying macroscopic structures, utilizing soft X-ray tomography to visually observe the multidimensional structures of metal-organic frameworks, such as core-shell and hollow frameworks, or different metal elements. The results demonstrate that soft X-ray tomography (SXT) provides a more intuitive means of observing the distribution of metals within the structure and identifying the types of hollow pores present in MOFs. This pioneering evaluation of MOFs via SXT showcases its outstanding performance in identifying multidimensional metal-organic framework structures.