(668a) Preparation of Mesh-Adjustable Molecular Sieve (MAMS) Thin Films and Membranes

Membrane-based gas separations are an energetically attractive alternative to traditional gas separation methods used to separate industrially important gas mixtures (such as cryogenic distillation).¹ Despite this sizeable advantage in energy consumption, membrane technology still occupies only a fraction of the current separations market. This is mainly due to the lack of new materials and processing methods.¹ Further, there are certain commercially important gas mixtures, such as propane/propene and nitrogen/methane, for which no membrane-based separation method is currently available. The main difficulty in using membranes to separate these mixtures is finding a material with a pore size that falls between their (unfortunately very similar) kinetic diameters.

Mesh-adjustable molecular sieves (hereafter MAMS) are a new material first developed and reported by Zhou and his coworkers.² They are a member of a class of materials known as metal-organic frameworks (hereafter MOFs).³ Like all MOFs, these MAMS consist of metal atoms bonded with flexible organic ligands in a regular, porous framework. However, MAMS are unique in that their organic ligands also act as temperature sensitive gates at the pores. This makes them capable of continuously adjusting their pore size in the range of 2.9 ? 5 Å.² Here we report for the first time the fabrication of thin films and membranes of one of these materials (MAMS-6) on porous supports (α-Al2O3) using microwave seeding and secondary growth. These films and membranes are made of continuous layers of randomly oriented, intergrown MAMS-6 crystals. This work is the first step toward developing membranes with controllable pore size to kinetically separate very similar gases.

[1] Baker, R.W. Ind. Eng. Chem. Res. 2002, 41, 1393-1411.

[2] Ma, S. Q.; Sun, D. F.; Wang, X. S.; Zhou, H. C. Angew. Chem., Int. Ed. 2007, 46, 2458-2462.

[3] Zacher, D.; Shekhah, O.; Woll, C.; Fischer, R. A. Chem. Soc. Rev. 2009, 38, 1418-1429.