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Adsorptive characterization and applications of carbon-­silica composite materials

Wednesday, 4 July, 2012 - 10:30
Campus: Brussels Humanities, Sciences & Engineering campus
Alexios Harkiolakis
phd defence

Recently proposed carbon-silica composite materials (CSM) were expected to
bridge a gap between mesoporous and microporous materials by using properties
of both structured mesoporous silica and broadly applicable carbonaceous
materials. CSM were prepared from mesoporous silica MCM-41 impregnated with
furfuryl alcohol, subsequently polymerized and pyrolyzed inside the pores at
elevated temperatures of around 1073K. Synthesis parameters were varied
systematically and the CSM studied with various adsorptive characterization
techniques. In the low coverage region, the enthalpies and entropies were more
comparable to those for a MFI microporous zeolite and very different from those
of mesoporous materials (MCM-41, MCM-48). Unexpected shape selectivity was
demonstrated at low coverage, but also breakthrough experiments as well as
vapor phase gravimetry showed an increased shape selectivity of linear versus
branched alkanes at high carbon loadings and high pyrolysis temperatures.
Polarity was investigated by water vapor phase adsorption isotherms and
adsorption isotherms of heptanol from heptanes in the liquid phase and indicated
the presence of polar surface groups. Clearly not all silica surface was covered
with carbon resulting in mixed behavior of carbon nano-particles inside the silica
pores. Ammonia treated and nitrogen plasma treated materials were investigated
for their carbon dioxide adsorption and carbon dioxide/methane separation
properties. The resulting carbon dioxide capacity is stable around 1 mmol/g but
the separation factor varies from 1 up to more than 11 depending on the
synthesis conditions, which is high in comparison to many adsorbent materials.
HPLC grade particles were synthesized by the pseudomorphic transformation of
uniform silica particles and pulse liquid chromatography of homologous series of
alkylbenzenes, polyaromatic hydrocarbons showed that the stationary phase
retention resembles a normal phase behavior with high interaction towards
phenyl groups and shape selective effects. Given their unique shape selectivity
and carbon nature, CSM could be applied in applications in catalytic reactions as
well as in adsorptive separations.