Seed-free synthesis of highly permeable zeolite NaA membranes through deposition of APTES-functionalized alumina particles on macroporous supports

Abstract

A new strategy through deposition of 3-aminopropyltriethoxysilane (APTES) functionalized Al2O3 particles on a coarse macrosporous tube with big defect holes was reported for seed-free synthesis of zeolite NaA membranes. Prior to the deposition of Al2O3 particles onto the macroporous support, APTES was covalently functionalized onto the surface of Al2O3 particles, aiming at providing heterogeneous sites for the growth of NaA zeolites on the support surface by serving as linker between the support and the silica and aluminum sources. Large APTES-Al2O3 particles were firstly deposited on the support surface to reduce the surface roughness and the effective pore sizes, subsequently the small APTES-Al2O3 particles were deposited on the support to provide plenty of heterogeneous nucleation sites for the growth of zeolite NaA crystals. In this way, a thin and continuous APTES-Al2O3 layer was formed on the support. After one single hydrothermal synthesis, a thin and compact zeolite NaA membrane with thickness of 2μm was achieved. The synthesized NaA membranes showed high fluxes of 3.7–3.9kgm−2h−1 with separation factors over 5000 in dehydrating the 90wt% ethanol/10wt% water mixtures at 75°C. The strategy presented in this study was expected to extend for preparation of other types of thin zeolite membranes on such coarse symmetric macroporous supports.