Seeded growth of high-performance ZIF-8 membranes in thick wall autoclaves assisted by modulator.

The preparation of thin metal-organic framework (MOF) membranes by seeded secondary growth method is still a challenge. In this study, relatively thin ZIF-8 membranes with high gas separation performance on alumina hollow fibers are prepared in autoclaves with thick-walled Teflon-liners by the seeded secondary growth method under the modulation of sodium formate. The ZIF-8 membrane thickness can be greatly decreased and the cracks in the membrane layer can be avoided by using thick-walled Teflon-liner (e.g., 7.5 mm) during secondary growth mainly due to the slow heating and cooling of the synthesis solution, which can control the nucleation rate and growth rate of crystals, leading to an appropriate membrane formation rate. A certain amount of sodium formate can introduce ZnO particles in the seed layer to improve the formation of dense ZIF-8 membrane layer and control the growth rate of membrane layer. The suitable amount of sodium formate and thick-walled Teflon-liner are crucial in ensuring the well-intergrowth of relatively thin ZIF-8 membranes. Owing to reduced grain boundary defects, the prepared ZIF-8 membranes show an ideal H 2 /N 2 separation selectivity of 30.9 ± 1.8, which is at least twice the highest value reported in the literature under similar separation conditions. Image 1 • Thin and dense ZIF-8 membranes obtained in a thick-walled Teflon-liner. • Thin and dense ZIF-8 membranes obtained by slow-heating up. • Appropriate sodium formate content, thickness of liner and seeds are important. • The highest H 2 /N 2 separation selectivity for ZIF-8 membranes reported so far. [ABSTRACT FROM AUTHOR]