Sorption isotherms of volatile molecules on micro- and mesoporous nanosized siliceous materials based on acoustic wave devices.

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).