Effect of sol–gel-based silica buffer layer on the formation of NaA zeolite membrane

The support substrates were modified with sol–gel-based silica coating as intermediate buffer layer followed by NaA zeolite seed (prepared hydrothermally at 85 °C for 3 h) coating with 2 wt% aqueous dispersion. The secondary crystallization of NaA zeolite in the silica-seed-coated supports was carried out hydrothermally through crystal growth process at 65 °C for 4 and 8 h (single-stage each), (6 + 4) and (6 + 6) h (double-stage each), and (6 + 4 + 2) and (6 + 4 + 4) h (triple-stage each). The crystallization behaviours of the prepared NaA membranes were studied by X-ray diffraction, and the microstructures of the same films were observed by field emission scanning electron microscope. The efficiency of the membranes was tested with gas permeation study. The double-stage secondary crystallization at 65 °C for (6 + 4) h showed highly interlocked NaA grains in the membrane and it rendered the permeance values of 3.7 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and 15.9 × 10⁻⁸ for single gas, nitrogen (N₂) and hydrogen (H₂) respectively with the ideal selectivity of 4.3.