Nanosized zeolite films for vapor-sensing applications

Colloidal zeolites LTA and BEA sized below 100 nm were synthesized as building blocks for the controlled growth of thin microporous films on piezoelectric sensor devices (quartz crystal microbalance, QCM). The zeolite films were prepared on pre-seeded gold substrates on QCM devices. Initially, a layer of colloidal particles was deposited on the support through chemical bonding with a silane coupling agent, followed by hydrothermal growth. BEA- and LTA-type zeolite films with thicknesses of 250 and 450 nm, respectively, were prepared by optimizing the synthesis conditions. The application of these zeolite films in microsensors for water and organic compounds is presented. The importance of the zeolite structure type with respect to the sensitivity towards different organic and water vapors at various concentrations is discussed. Both zeolites are thermally stable and show reproducible responses during long-term experiments. Based on these results, it was concluded that both zeolite films could be used effectively as humidity sensor materials for water vapor sensing purposes. High sensitivity, good reversibility and long life were demonstrated for this type of zeolite film at low water concentrations. In comparison to LTA, the BEA films show a higher sorption capacity towards water vapor and no rejection of pentane, hexane and cyclohexane, due to the larger pore size of the BEA structure.