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CO 2 sorption of a thin silica layer determined by spectroscopic ellipsometry
Author(s) -
Benes Nieck E.,
Spijksma Gerald,
Verweij Henk,
Wormeester Herbert,
Poelsema Bene
Publication year - 2001
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690470527
Subject(s) - sorption , ellipsometry , porosity , materials science , adsorption , layer (electronics) , arrhenius equation , langmuir , amorphous solid , analytical chemistry (journal) , chemical engineering , silica gel , thin film , composite material , chemistry , chromatography , crystallography , nanotechnology , activation energy , engineering
Optical properties of a thin amorphous silica membrane and the supported γ‐alumina layer on which it was coated were obtained from spectroscopic ellipsometry. The thicknesses of γ‐alumina and silica layers from ellipsometric spectra were 1.654 μm and 73 nm, respectively. The porosity of the γ‐alumina layer was 51%. The porosity of the silica layer (15–25%), appeared to be smaller than that of unsupported silica material prepared by a similar method. Determination of the porosity of the silica layer, however, was quite inaccurate, because optical properties of the pure material were not exactly known. Ellipsometry was also used to determine the sorption behavior of CO 2 in the γ‐alumina and silica layers. For both layers the observed sorption behavior could be described by a Langmuir isotherm (c CO 2 , max= 0.84 and 2.8–3.0 mmol·g −1 , respectively), with Arrhenius‐type temperature dependence (sorption heat 24.6±1.0 and 27.0±1.3 kJ·mol −1 , respectively). The adsorption behavior of supported and unsupported γ‐alumina appeared to be similar. The heat of sorption was larger for supported thin silica layers than for unsupported bulk silica, suggesting smaller pores in the thin layer.