Synthesis of multi-layer zeolite LTA membranes with enhanced gas separation performance by using 3-aminopropyltriethoxysilane as interlayer

A facile strategy for the layer-by-layer synthesis of sandwich-like zeolite LTA membranes by using 3-aminopropyltriethoxysilane (APTES) as modifier is reported. APTES reacts with surface hydroxyls and forms a covalently bonded siloxane interlayer. APTES treatment is helpful to promote nucleation and growth of the zeolite LTA layer on solid surfaces. Further, the covalently bonded self-assembled siloxane film can protect the already formed LTA layer from dissolution and transformation during the next hydrothermal LTA synthesis step, thus facilitating the formation of well intergrown and phase-pure multi-layer zeolite LTA membranes. The multi-layer zeolite LTA membranes display molecular sieving performance, and each additional LTA layer improves the selectivity of the sandwich-like LTA layer stack. In mixed gas separation at 100 °C, the mixture separation factors for equimolar mixtures of H2/CO2, H2/N2, H2/CH4 and H2/C3H8, on the single/multi-layer LTA zeolite membranes in the Na+ state are found to be 6.3, 5.6, 4.3 and 6.5 (single-layer), 8.8, 7.2, 5.8 and 12.6 (double-layer), and 12.5, 8.6, 6.5 and 19.3 (triple-layer).

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► Sandwich-shaped multi-layer LTA membranes with shape-selectivity were prepared.
► With increasing number of the LTA layers, the mixed gas selectivities increase.
► Subsequent layers show an increasing (2 2 2) orientation relative to the first layer.