Metal-Organic Framework UiO-66 Layer: A Highly Oriented Membrane with Good Selectivity and Hydrogen Permeance

The 3D metal organic framework (MOF) structure UiO-66 [Zr6O4(OH)(4)(bdc)(6)], featuring triangular pores of approximately 6 angstrom, has been successfully prepared as a thin supported membrane layer with high crystallo-graphic orientation on ceramic alpha-Al2O3 supports. The adhesion of the MOF layer to the ceramic support was investigated in different taxing conditions. Furthermore, by coating this UiO-66 membrane with a thin polyimide (Matrimid) top layer, we prepared a multilayer composite. Said membranes have been evaluated in the separation of hydrogen (H-2) from different binary mixtures at room temperature. H-2 as the smallest molecule (2.9 angstrom) should pass the UiO-66 membrane preferably since the kinetic diameters of all the other gases under study are larger. The gas mixture separation factors for the neat UiO-66 membrane were indeed found to be H-2/CO2 = 5.1, H-2/N-2 = 4.7, H-2/CH4 = 12.9, H-2/C2H6 = 22.4, and H-2/C3H8 = 28.5. The coating with Matrimid led to a sharp cutoff for gases with kinetic diameters greater than 3.7 angstrom, resulting in increased separation performance.