Optimized Acetylene/Carbon Dioxide Sorption in a Dynamic Porous Crystal

The low compression limit of acetylene (C2H2) and its similarity to carbon dioxide (CO2) challenge the development of novel adsorbents. We illustrate in this report that the unique static and dynamic pore characteristics of a metal azolate framework, [Cu(etz)]n (MAF-2, Hetz = 3,5-diethyl-1,2,4-triazole), can combine to show extraordinary C2H2/CO2 sorption behaviors, which have been elucidated by a combination of gas sorption measurements and single-crystal structure analyses of the sorption complexes of both C2H2 and CO2. As demonstrated by single-crystal X-ray crystallography, C2H2/CO2 hexamers are confined inside the nanocages of MAF-2 in different configurations. The subtle difference between C2H2 and CO2 is magnified by consequent framework dynamics, which produce sigmoid isotherms that are optimized for practical adsorptive applications. Large C2H2 uptake (70 cm3 g−1) and high C2H2/CO2 uptake ratio (3.7) at 298 K, 1 atm as well as facile gas desorption are revealed. Since the C2H2 uptake at 298 K, 1 atm is far from saturation (119 cm3 g−1), MAF-2 permits a usable C2H2 storage capacity 20 times higher than its volume or 40 times higher than that of a gas cylinder working between practical limits of 1.0−1.5 atm.

乙炔（acetylene, C₂H₂）的低压缩极限及其与二氧化碳（carbon dioxide, CO₂）的理化相似性，给新型吸附剂的开发带来了显著挑战。本研究表明，一种金属唑酸盐骨架（metal azolate framework）材料[Cu(etz)]ₙ（MAF-2，其中Hetz=3,5-二乙基-1,2,4-三唑）所具备的独特静态与动态孔道特性，可协同展现出优异的乙炔/二氧化碳吸附分离性能；该性能通过气体吸附测试以及乙炔、二氧化碳吸附复合物的单晶结构分析得到了系统阐明。单晶X射线晶体学（single-crystal X-ray crystallography）表征结果显示，乙炔与二氧化碳的六聚体分别以不同构型被限域在MAF-2的纳米笼中。二者之间的细微性质差异被后续的骨架动态效应放大，从而形成了适配实际吸附应用的S型吸附等温线（sigmoid isotherms）。实验结果表明，在298 K、1 atm条件下，该材料具备较高的乙炔吸附量（70 cm³ g⁻¹）、优异的乙炔/二氧化碳吸附量比（3.7），且气体脱附过程简便易行。由于298 K、1 atm下的乙炔吸附量远未达到饱和吸附容量（119 cm³ g⁻¹），MAF-2的可用乙炔存储容量可达其自身体积的20倍，或是在1.0~1.5 atm实用压力范围内工作的钢瓶存储容量的40倍。