Surface Properties of Silica-Based Biomaterials: CaSpecies at the Surface of Amorphous Silica As Model Sites
Articolo
Data di Pubblicazione:
2008
Abstract:
The adsorption of CH3OH vapor at the surface of Ca-modified silica was studied by means of the combined
use of an experimental and a theoretical approach. Parallel IR spectroscopic and microcalorimetric experiments
were performed to describe quantitatively and energetically the surface features of nanosized Ca-modified
specimens (A200/Cax, activated in mild conditions) as a function of Ca loading and in comparison with the
unmodified parent silica (Aerosil 200). The presence of Ca species at the surface enhances the adsorption
capacity with respect to the unmodified parent silica and creates a rather complex reactivity. Ab initio simulation
provided microscopic information on the energetic of coordinated CH3OH adducts formed at the Ca sites
(BE ) 104 kJ/mol vs qdiff ∼ 100 kJ/mol) and on the possible reaction path toward products. The methoxylation
of the surface, yielding Si-OCH3 and Ca-OH species (and not Ca-OCH3 and Si-OH) occurs only to a
limited extent (30-40% of the total methanol uptake) and depends on both CH3OH pressure and time contact,
according to the activated reaction pathway, as provided by ab initio simulation. Data from both
volumetric-calorimetric and IR spectroscopic experiments indicated, in good agreement with ab initio
simulation results, that the overall interaction involves both chemical and physical adsorption processes which,
to a large extent, occur simultaneously, the relevant energy transfers being very similar.
Tipologia CRIS:
03A-Articolo su Rivista
Elenco autori:
Vera Bolis; Claudia Busco; Valentina Aina; Claudio Morterra; Piero Ugliengo
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