Abstract: Permeation and separation properties for CO₂/N₂ mixtures with high quality, thin (～8.8 μm) zeolitic imidazolate framework-8 (ZIF-8) membranes prepared by the secondary growth method were studied at different temperatures and feed pressures. The crystal structure, surface coverage, uniformity of the prepared ZIF-8 seeding layers and membranes were characterized by using SEM and XRD. The low concentration of the seed suspension and subsequent dip-coating method helped to obtain a more uniform, continuous and ultrathin ZIF-8 seeds layer of support; the synthesized ZIF-8 membranes offered selective permeation for CO₂ over N₂ with CO₂/N₂ mixture feed under the experimental conditions studied. The separation factor of CO₂/N₂ mixed gas through a ZIF-8 film decreased with increasing temperature, but increased with increasing feed pressure. Its separation factor of CO₂ over N₂ could reach 6 at 298 K, 406 kPa, and CO₂ content of 50%, exceeding the Knudsen diffusion selectivity.

Key words: ZIF-8 membrane, secondary growth, gas permeation, CO₂/N₂ mixture gases, separation performance

摘要： 采用二次生长法在α-Al₂O₃载体上制备超薄型ZIF-8膜，研究了多种轻分子气体以及混合气体CO₂/N₂的渗透分离性能。通过SEM和XRD表征了ZIF-8晶种层的晶种涂布状态，以及ZIF-8晶体膜的生长覆盖度和晶膜厚度。研究结果表明：采用低浓度的晶种悬浮液通过浸润式连续多次涂布法，有利于获得晶种层厚度均匀且覆盖度高的超薄均匀ZIF-8晶种层，经过二次生长后所得ZIF-8膜的覆盖度高、厚度均匀且较薄，仅约为8.8 μm；在所测试范围内的CO₂/N₂混合气体中，此ZIF-8膜对CO₂具有优先选择透过性，其对CO₂/N₂的渗透分离因子随温度的升高而降低，随渗透压力的增加而增加，在298 K、406 kPa和CO₂组分含量为50%时，该分离因子能达到6，显著超过Knudsen扩散的分离系数。

关键词: ZIF-8膜, 二次生长法, 气体渗透扩散行为, CO₂/N₂混合气, 分离性能