| 摘要: | 隨著全球氣候變遷與碳排放議題越來越受到關注，開發高效且永續性的二氧化碳捕捉技術已成為當前需研究的方向。金屬有機框架擁有高的比表面積、可調控孔徑與官能化潛力，成為次世代 CO₂ 吸附材料的研究重點。ZIF-7及胺基衍生物 NH₂-ZIF-7，兼具微孔結構與熱穩定性，具良好的吸附潛力。
然而，純ZIF-7對於CO₂吸附能力有限。本研究利用深共熔溶劑(DES)作為表面修飾劑，進一步去提升材料對 CO₂ 的吸附量。DES 為一種由氫鍵供受體組合而成的低成本綠色溶劑，具有製備簡易、環境友善及官能基可調性等優勢，能有效引入極性官能基，改善材料表面化學性質並增強 CO₂ 吸附能力。研究中選用氯化膽鹼作為氫鍵的接受體，再分別與尿素及乙醇胺作為氫鍵的提供體，兩者混合形成DES，將DES修飾於ZIF-7與NH₂-ZIF-7的表面。透過 FTIR、SEM、EDS、XRD、BET、TGA等分析來去探討修飾對材料結構與孔性變化的影響，最後進行使用HPTGA來去測試材料的 CO₂ 吸附等溫線測試以評估吸附性能。
首先從FTIR及DSC的結果證明了，我們成功的合成出DES (Urea)及DES (MEA)，接著從FTIR、XRD、SEM、EDS、TGA等結果證實了DES有成功修飾於MOF表面，同時也證實了經胺基化後的ZIF-7衍生物NH2-ZIF-7，可以使DES更好的去修飾於MOF的表面。從BET的結果觀察到，經DES修飾後樣品的比表面積與微孔體積均明顯下降，尤其在DES (MEA)中的表現更為明顯，顯示部分孔道可能因DES分子尺寸過大而導致阻塞的現象。用目前已停產之儀器HPTGA來去測試二氧化碳的吸附性能，在298K、1atm下，未修飾ZIF-7和NH₂-ZIF-7吸附量分別為2.08 mmol/g及1.03 mmol/g，而DES@ZIF-7(Urea)與(MEA)分別下降至1.47 mmol/g和1.86 mmol/g DES@NH₂-ZIF-7(Urea)與(MEA)分別下降至0.68 mmol/g和0.86 mmol/g。這結果判斷在超微孔框架中，DES雖然提供了表面極性，但因空間佔據效應可能反而抑制氣體進入孔道，降低吸附性能。
本研究證實了DES與MOF的相容性對CO₂吸附表現有著關鍵影響。未來應針對更小分子的氫鍵提供體或孔徑較大的MOF架構進行設計優化，以發揮DES功能化的最大潛力，提供碳捕捉應用的新策略與參考方向。
;With increasing attention to global climate change and carbon emissions, pursuing sustainable and high-performance carbon capture methods is now a key priority in scientific research. Metal organic frameworks (MOFs), it has functionalization potential, tunable pore sizes, and high surface areas, have emerged as promising next generation CO₂ adsorbents. Among them, ZIF-7 and its amino-functionalized derivative, NH₂-ZIF-7, possess microporous structures and thermal stability, showing good CO₂ adsorption potential.
However, the CO₂ uptake capacity of pristine ZIF-7 remains limited. In this study, Deep eutectic solvents (DESs) were utilized as surface-functionalizing agents to enhance the CO₂ adsorption. DES is a low-cost and green solvent composed of hydrogen bond donors and acceptors. It offers advantages such as simple preparation, environmental friendliness, and tunable functional groups. These features allow for the effective introduction of polar functionalities, which improve the surface chemistry of the material and enhance its CO₂ adsorption capacity. Choline chloride was selected to be the hydrogen bond acceptor, while urea and monoethanolamine (MEA) were used as hydrogen bond donors to construct DESs. Surface modification of ZIF-7 and NH₂-ZIF-7 was carried out using the synthesized DESs. Textural and structural changes resulting from the modification were using FTIR, SEM, EDS, XRD, BET, TGA analyses. CO₂ adsorption performance was assessed through isothermal measurements conducted using High Pressure Thermogravimetric Analyzer (HPTGA).
FTIR and DSC results confirmed the successful synthesis of DES (Urea) and DES (MEA). Further FTIR, XRD, SEM, EDS, and TGA characterizations verified that the DESs were successfully loaded onto the MOF surfaces. It was also confirmed that the amino-functionalized NH₂-ZIF-7 enhanced the DES dispersion on the MOF surface. According to BET analysis, both the surface area and micropore volume of the samples were reduced following DES modification, with DES (MEA) modified samples showing the most pronounced effect, indicating potential pore blockage due to the large molecular size of MEA. CO₂ adsorption performance was measured by using the HPTGA, a now-discontinued instrument. At the temperature of 298 K and pressure of 1 atm, the CO₂ capacities of pristine ZIF-7 and NH₂-ZIF-7 were 2.08 and 1.03 mmol/g, respectively. After modification, the uptake of DES@ZIF-7 (Urea) and (MEA) decreased to 1.47 and 1.86 mmol/g, respectively, while DES@NH₂-ZIF-7 (Urea) and (MEA) decreased to 0.68 and 0.86 mmol/g. These results suggest that although DESs introduce surface polarity, the steric hindrance caused by their molecular size may hinder gas diffusion into the ultra-micropores, thereby reducing adsorption efficiency.
The findings highlight that DESs and MOF compatibility a key factor influencing CO₂ adsorption behavior. Future research should explore smaller hydrogen bond donors or MOFs with larger pore apertures to maximize the benefits of DES functionalization and provide a novel strategy for advanced carbon capture applications. |
