pH dependence of the crystal violet adsorption isotherm at the silica-water interface.
J Phys Chem B
; 109(30): 14475-80, 2005 Aug 04.
Article
em En
| MEDLINE
| ID: mdl-16852824
ABSTRACT
The pH-dependent adsorption isotherms for the charged chromophore crystal violet, CV(+), have been measured with three different bases by a free-running cavity implementation of evanescent wave cavity ring-down spectroscopy. The ratio of the maximal absorbance measurements at pH 5.10 and 9.05 is consistent with a Q2Q3 silanol site ratio of 72.827.2. The adsorption isotherms have been interpreted in terms a cooperative binding adsorption allowing more than one ionic species to bind to each silanol group. The surface concentration is consistent with a silanol charge density of 1.92 +/- 0.55 nm(-2) and a total neutralized interface layer structure extending 9 nm from the surface. Binding constants and stoichiometric coefficients are derived for CV(+) to both the Q2 and Q3 sites. A variation of the adsorption isotherm with base is observed so that the isotherm at pH 9.05 adjusted with ammonium hydroxide sets up a competitive acid-base equilibrium with the SiOH groups with only 49% of the surface silanol sites dissociated. The implications for functionalized surfaces in chromatography are discussed.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Água
/
Dióxido de Silício
/
Violeta Genciana
Idioma:
En
Revista:
J Phys Chem B
Assunto da revista:
QUIMICA
Ano de publicação:
2005
Tipo de documento:
Article
País de afiliação:
Reino Unido