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Darga, Alex (2007): Sorption isotherms of volatile molecules on micro- and mesoporous nanosized siliceous materials based on acoustic wave devices.: Determination of corresponding isosteric heats of adsorption. Dissertation, LMU München: Faculty of Chemistry and Pharmacy
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Abstract

Microporous zeolites and mesoporous periodically silicious materials offer interesting features, like porosity in general, host-guest interactions and among others, sorption phenomena. The application of addressable individual material pixels, pin-printed onto adequate pre-treated supporting surfaces for gas-sensor systems was evaluated. The contact pin-printing technique, well known in bio-science, was adopted and optimized. The successful deposition of colloidal suspensions of zeolite materials on Au-covered glass slides with chemically attached intermediate anchoring molecules was demonstrated on a 100 μm scale (chapter 3). In a collaboration with the physical department of the LMU Munich (Prof. Kotthaus) a gas sensor system, based on surface acoustic wave devices was developed. Thin layers of porous material in the sub-microgram range were applied, in order to record adsorption isotherms and to determine the released heat of adsorption of specific analyte gases. Related to very small sample amounts and short diffusion times the necessary experimental measurement time could be reduced down to several minutes (chapter 9). An existing rudimentary quartz crystal microbalance (QCM) was enhanced and an automated intelligent equilibrium system was developed. Furthermore, the system was equipped with liquid mass controllers in order to measure the sorption properties together with vaporized liquid solvents (chapter 4). The developed QCM measurement setup was applied as advanced research tool in order to investigate sorption properties of various porous samples and to obtain the thermodynamic parameter, the isosteric heat of adsorption. The incorporation of organic moieties into siliceous frameworks leads to a wide variety of adsorbate–adsorbent interactions including weak Van-der-Waals attractions as well as strong interactions such as Coulomb forces. Depending on the desired properties of such substituted highly porous matrix materials, optimized synthesis routes can be established to enhance the desired internal pore surface–affinity towards certain volatile compounds. Based on a fundamental knowledge of the host–guest system, sorption related applications may benefit from individually fine-tuned and modified sample materials. The sorption isotherms and isosteric heat of adsorption for non-modified, phenyl- Summary IIIIIIIII modified, cyano-modified, vinyl-modified and mercapto-functionalized mesoporous material for ethanol and 1-butanol sorption were determined. Additionally, nanosized zeolites, like ZSM-5, Sil-1 and zeolite beta were investigated (chapter 6). Furthermore, sorption isotherms of vaporized toluene on non-modified and phenyl-functionalized mesoporous silica samples were determined using the gravimetric QCM technique at different temperatures. The mesoporous silica was modified by in situ via co-condensation and via post-synthesis grafting approaches, respectively. All samples were thoroughly characterized by several standard techniques and additionally with toluene sorption experiments on the automated QCM setup. The different heats of adsorption of toluene on the various modified silica surfaces obtained by the sorption data made it possible to gain additional information about the degree and type of surface functionalization. It is thus demonstrated that QCM studies can be a powerful and convenient tool for efficient investigations of functionalized mesoporous silica particles that yield valuable quantitative information on molecule-surface interactions (chapter 8).