The syntheses of high quality zeolite thin films often involve arrangement of preformed zeolite seed nanocrystals onto a surface followed by crystallisation. The quality of the resulting films depends on the properties of the seed layer and efforts have focused on developing techniques for depositing improved seed layers. Methods such as dip/spin-coating, electrostatic, electrophoretic and ultrasonic deposition have been reported in the literature. Here, we report on the arrangement of preformed Silicalite-1 crystals on silicon wafers by the Langmuir-Blodgett method.

Silicalite-1 crystals with a size of about 100 nm were prepared from clear synthesis solutions containing tertaethoxysilane, tetrapropylammonium hydroxide and distilled water by hydrothermal treatment at 100ºC for 24 h. The zeolite suspension (ca. 1 wt.% concentration) was used after purification by three-time centrifugation and redispersion in distilled water. A film of cationic surfactant was prepared in a Langmuir-Blodgett trough by spreading a solution of octadecylamine (ODA) in chloroform on water subphase containing NaCl. Silicalite-1 suspension was then spread directly onto the subphase covered with a layer of octadecylamine. The influence of Silicalite-1 amount, equilibrium time of interaction between Silicalite-1 and ODA, subphase pH and ionic strength was studied by recording the pressure-area isotherms. Langmuir-Blodgett films were transferred to silicon wafers precleaned in piranha bath under different surface pressures. Denser Silicalite-1 films were prepared by steaming the seeded silicon wafers in autoclaves at 150ºC. The Langmuir-Blodgett seed films and the films after steaming were studied by scanning electron microscopy, atomic force microscopy, X-ray diffraction and attenuated total reflection.

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