Ordered mesoporous membranes: Effects of support and surfactant removal conditions on membrane quality

Ordered mesoporous MCM-48 membranes with cubic pore structure were prepared by solution growth method and characterized by XRD, SEM/EDS and unsteady-state gas permeation. The membranes were fabricated on symmetric α-alumina supports of different pore sizes under hydrothermal conditions using cetyltrimethylamonium bromide (CTAB) as a surfactant. The surfactant was removed by calcination and Soxhlet extraction at 100 °C using ethanol/HCl mixture. The X-ray diffraction showed that these membranes possessed a cubic MCM-48 pore structure. The N₂ adsorption studies at 77 K indicated high pore volumes and pore size distribution in the mesoporous regime with an average pore diameter of ∼2.6 nm. The membranes prepared on the A15 α-alumina support (0.3 μm average pore size) exhibited the presence of pinhole defects. The single gas N₂ and CO₂ permeation experiments showed that the best quality membranes were synthesized on the α-A16 alumina supports (average pore size ∼0.2 μm) when the surfactant was removed by Soxhlet extraction. For these membranes the N₂ and CO₂ permeation was found to be governed by Knudsen diffusion. The permeance was independent of the feed pressure, indicating the absence of viscous flow contribution to gas transport.