Zeolite crystal layers coupled to piezoelectric sensors

Abstract

Microporous zeolite crystals were successfully coupled onto the gold electrodes of quartz crystal microbalances (QCM). A self-assembled monolayer of thiol-alkoxysilane coupling agent on the gold surface was used as the interfacial layer to promote adhesion of the zeolite crystals to the QCM. The resulting, densely packed single layers of zeolite crystals were stable to at least 625 K. Transient sorption behavior of organic vapor pulses, dynamic vapor sorption isotherms and nitrogen sorption isotherms at liquid nitrogen temperature were examined to characterize the zeolite-coated QCMs. Depending on the type of zeolite coating, the resonance frequency response to vapor pulses could be increased up to 500-fold compared to the bare QCM. The regular micropores (0.3-0.8 nm) of the QCM-attached zeolite crystals were found to control molecular access into the extensive intrazeolite volume. Selectivity of the frequency response in excess of 100:1 toward molecules of different size and/or shape could be demonstrated. An additional recognition mechanism based upon intrazeolite diffusion rates was also established.