Facile synthesis of zeolite FAU molecular sieve membranes on bio-adhesive polydopamine modified Al₂O₃ tubes

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite FAU membranes through mussel-inspired polydopamine (PDA) modification of porous Al₂O₃ tubes. Zeolite FAU nutrients can be attracted and bound to the support surface via the formation of strong non-covalent and covalent chemical bonds, thus promoting the nucleation and growth of uniform, well-intergrown and phase-pure zeolite FAU membranes. The SEM and XRD characterizations demonstrate that a relative thin but dense and pure-phase zeolite FAU membrane with a thickness of about 2.3μm can be obtained on the PDA-modified Al₂O₃ tube after crystallization at 75°C for 24h, and no visible cracks, pinholes or other defects are observed on the membrane layer. The zeolite FAU membrane prepared at 75°C for 24h was evaluated in single gas permeation and mixed gas separation. For binary mixtures at 50°C and 1bar, the mixture separation factors of H₂/CH₄ and H₂/C₃H₈ are 9.9 and 127.7, respectively, which are much higher than the corresponding Knudsen coefficients. And relative high H₂ permeance of about 1.9×10^-7molm^-2s^-1Pa^-1 can be obtained through the FAU membrane due to the thin layer and the relative wide pore size of 0.74nm, demonstrating a viable direction for promising application of FAU membranes in hydrogen purification and separation.