(733c) A General Method for the Preparation of ZIF Membranes: Effect of Surface Modification and Growth Conditions
Zeolitic imidazolate frameworks (ZIFs), a subset of metal-organic frameworks (MOFs), exhibit zeolitic topologies and drastically increased chemical and thermal stability compared to other MOFs1-3. This stability of ZIFs enables the materials to be useful for many applications, in particular, for gas storages and separations 4. For examples, several ZIFs have shown high CO2 selectivity and sorption capacity. It infers that a membrane made from these materials could be of great interest for CO2 separations. Bux et al5 has recently reported the first ZIF membrane by growing in situ on porous titania supports using microwave irradiation. More recently more ZIF membranes were prepared by either in situ6 or secondary growth7. However, each synthesis method is for specific type of ZIFs. In order to advance the applications of ZIF films and membranes in practical purposes including membrane-based gas separation, it would be desirable to develop a general technique to fabricate continuous ZIF thin films and membranes. Here we report a novel general method to fabricate ZIF membranes. The key idea is to modify porous supports (á-alumina) with organic ligands (i.e., imidazolate and its derivatives) prior to the crystallization. It was found that the linkers attached on the á-alumina surface induce in situ crystallization of ZIF crystals during solvothermal treatment in the presence of sodium formate, a deprotonator. It turns out that in the absence of sodium formate ZIF films are poorly-intergrown even though they are uniform throughout the supports. We will present the role of sodium formate in determining ZIF membrane microstructure and propose a mechanism to explain the effect of sodium formate on the membrane microsture. We will compare our results to those in the recent literature. Surface modification with organic linker proved to be general for other ZIFs. Finally, the gas permeation properties of ZIF-8 and ZIF-7 membranes will be discussed.
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