Direct synthesis of ZSM-5 crystals on gold modified by zirconium-phosphonate multilayers

Thin zeolite films are of interest in selective membranes and in dilute gas sensors. The effect of composition, pH, aging, and duration of synthesis on integrity of thin ZSM-5 films on Au surfaces was evaluated. Substrates were prepared by sputtering Au onto mica supports, followed by modification of these Au surfaces by zirconium-phosphonate multilayers to help induce nucleation. These substrates were then immersed into synthesis solutions. When high pH (∼13) solutions were used, crystallization on the substrate surface could not be achieved due to peeling off the Au layer from the support. Low pH (∼7.5) solutions resulted in large ZSM-5 crystals on the substrate surface, but without formation of a continuous film. Crystal growth was monitored by visually evaluating substrates after different periods of time during synthesis. Small crystals were observed on the surface at the earlier stages of crystallization. It was also observed that fully-grown crystals were formed on the substrate surface in half of the time required for the completion of crystallization (all gel consumed) in the bulk solution, and that there were more crystals on the surface earlier in the synthesis compared to when synthesis was complete. In all cases studied, crystals grew in isolated "islands"; never as a continuous film. Aging gels at room temperature had no effect on the films formed.