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.