Template-Free Synthesis of Highly b-Oriented MFI-Type Zeolite Thin Films by Seeded Secondary Growth.

Highly b-oriented, closely packed, MFI zeolite films are prepared on seeded stainless-steel plates using organic template-free, secondary growth solutions, containing aluminum sulfate as a crystallization agent. The number of a-oriented twin crystals is significantly reduced, and even eliminated, simply by restricting the pH value of the secondary growth solution to the narrow range of 11.1-11.3. Values of pH can be adjusted through the controlled addition of (NH4 )2 SO4 or H2 SO4 to secondary growth solutions of the composition (1 SiO2 :0.57 NaOH:137.5 H2 O:0.0050 (Al2 (SO4 )3 ⋅18 H2 O)) or by simply decreasing the molar composition of NaOH with no extra additives.