title: Elucidating the Sorption Mechanism of Dibromomethane in Disordered Mesoporous Silica Adsorbents.
abstract: The mechanism of dibromomethane (DBM) sorption in mesoporous silica was investigated by in situ small-angle X-ray scattering (SAXS). Six different samples of commercial porous silica particles used for liquid chromatography were studied, featuring a disordered mesoporous structure, with some of the samples being functionalized with alkyl chains. SAXS curves were recorded at room temperature at various relative pressures P/P0 during adsorption of DBM. The in situ SAXS experiment is based on contrast matching between silica and condensed DBM with regard to X-ray scattering. One alkyl-modified silica sample was evaluated in detail by extraction of the chord-length distribution (CLD) from SAXS data obtained for several P/P0. On the basis of this analytical approach and by comparison with ex situ obtained data of nitrogen and DBM adsorption, the mechanism of DBM uptake was studied. Results of average mesopore sizes obtained with the CLD method were compared with pore size analysis using nitrogen physisorption (77 K) with advanced state-of-the-art nonlocal density functional theory (NLDFT) evaluation. The dual SAXS/physisorption study indicates that microporosity is negligible in all silica samples and that surface functionalization with a hydrophobic ligand has a major influence upon the process of DBM adsorption. Also, all of the mesopores are accessible as evidenced by in situ SAXS. The data suggest that no multilayer adsorption occurs on C18-(octadecyl-)modified silica surfaces using DBM as adsorptive, and it is possibly also negligible on bare silica surfaces.
authors.affiliation: †Institute of Physical Chemistry, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 58, 35392 Gießen, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Stoeckel
authors.affiliation: ‡Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Wallacher
authors.affiliation: §Institute of Mechanics, Montanuniversität Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria.
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Zickler
authors.affiliation: ∥Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, Florida 33426, United States.
authors.forename: Matthias
authors.initials: M
authors.lastname: Thommes
authors.affiliation: †Institute of Physical Chemistry, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 58, 35392 Gießen, Germany.
authors.forename: Bernd M
authors.initials: BM
authors.lastname: Smarsly