(40c) Mesh-Adjustable Molecular Sieve (MAMS) Membranes for Gas Separation

Mesh adjustable molecular sieves (MAMS) are a new class of hybrid organic-inorganic microporous materials which exhibit temperature tunable molecular gates within their pores (1, 2). These gates afford control over the gases absorbed into the material by discriminating based on molecular size; a property that is of particular interest for membrane-based gas separation. A membrane capable of continuously adjusting its pore size would be applicable not only for separation of very similar gases (i.e. olefin/paraffin or butane isomers) but would be useful for its market flexibility (a single membrane could be used to achieve separation of many different gas mixtures). Another important feature of MAMS is that although the molecular gates within the structure open and close with temperature, the lattice constants do not change. This means that, unlike previously reported titanosilicate molecular sieves, the MAMS unit cell is unaffected by the molecular gating effect (2, 3). Recent reports describe the properties of MAMS in powder form, however no reports exist describing MAMS films or membranes. Here we discuss our progress developing MAMS membranes. A recently reported film fabrication technique, thermal seeding, was used to fabricate continuous MAMS membranes (4). Thermal seeding consists of seeding porous supports at high temperature with pre-synthesized crystals followed by solvothermal secondary growth to fabricate intergrown polycrystalline films. This technique was varied from the original report and the effect of this variation on the mechanical adhesion of MAMS membranes to porous supports was investigated. The molecular structure of MAMS-4 and MAMS-6 consists of metal clusters (copper paddlewheels) connected in a rigid hexagonal lattice by organic ligands. It was found that seeding porous supports with either copper only, organic ligands only, or pre-synthesized MAMS crystals all result in well-intergrown films after solvothermal growth in strong contrast to reported HKUST-1 membranes by thermal seeding (4). The ultimate goal of this work is to develop MAMS membranes with controllable permeability for gas separations.

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