Orientation and electronic structure of ion exchanged dye molecules on mica: An X-ray absorption study

Journal Article · Sun Feb 15 04:00:00 EST 1998 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1997.5296· OSTI ID:616326

Fischer, D; Caseri, W R; Haehner, G ^[1]

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1. ETH Zuerich (Switzerland)

Dye molecules are frequently used to determine the specific surface area and the ion exchange capacity of high-surface-area materials such as mica. The organic molecules are often considered to be planar and to adsorb in a flat orientation. In the present study the authors have investigated the orientation and electronic structure of crystal violet (CV) and malachite green (MG) on muscovite mica, prepared by immersing the substrates for extended periods into aqueous solutions of the dyes of various concentrations. The K{sup +} ions of the mica surface are replaced by the organic cations via ion exchange. X-ray photoelectron spectroscopy reveals that only one amino group is involved in the interaction of CV and MG with the muscovite surface, i.e., certain resonance structures are abolished upon adsorption. With near edge X-ray absorption fine structure spectroscopy a significant tilt angle with respect to the surface was found for all investigated species. A flat orientation, as has often been proposed before, can effectively be ruled out. Hence, results are in marked contrast to the often quoted orientation and suggest that the specific surface areas determined with dyes may, in general, be overestimated.

• Sponsoring Organization: Swiss National Science Foundation, Bern (Switzerland); USDOE, Washington, DC (United States)
• OSTI ID: 616326
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 198; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DYES
ELECTRONIC STRUCTURE
ION EXCHANGE
MUSCOVITE
ORIENTATION
POTASSIUM
SORPTIVE PROPERTIES
SURFACE AREA