Orientation and Electronic Structure of Ion Exchanged Dye Molecules on Mica: An X-Ray Absorption Study

Dorothee Fischer, Walter R Caseri, Georg Hähner

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37 Citations (Scopus)

Abstract

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 we 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+ 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, our 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. (C) 1998 Academic Press.

Original languageEnglish
Pages (from-to)337-346
Number of pages10
JournalJournal of Colloid and Interface Science
Volume198
Issue number2
Publication statusPublished - 15 Feb 1998

Keywords

  • silicates
  • muscovite mica
  • specific surface area
  • ion exchange
  • triphenylmethane dyes
  • crystal violet
  • malachite green
  • orientation
  • X-ray spectroscopy
  • NEXAFS
  • XPS
  • FINE-STRUCTURE SPECTROSCOPY
  • METHYLENE BLUE ABSORPTION
  • CRYSTAL VIOLET
  • FILLED POLYPROPYLENE
  • CATION-EXCHANGE
  • CLAY-MINERALS
  • SURFACE AREAS
  • LAYERS
  • MONTMORILLONITE
  • CAPACITIES

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