pH Dependence of the Crystal Violet Adsorption Isotherm at the Silica−Water Interface

Fisk, Jonathan D., Batten, Robin, Jones, Glenn , O'Reilly, Josephine P. and Shaw, Andrew M. (2005) pH Dependence of the Crystal Violet Adsorption Isotherm at the Silica−Water Interface. The Journal of Physical Chemistry B, 109 (30). pp. 14475-14480. ISSN 1520-6106

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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 Q2:Q3 silanol site ratio of 72.8:27.2. 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.

Keywords:Interfaces, Adsorption isotherms, Isotherms, Absorption, Layers
Subjects:F Physical Sciences > F170 Physical Chemistry
F Physical Sciences > F360 Optical Physics
F Physical Sciences > F110 Applied Chemistry
F Physical Sciences > F361 Laser Physics
F Physical Sciences > F100 Chemistry
F Physical Sciences > F180 Analytical Chemistry
Divisions:College of Science > School of Geography
ID Code:47603
Deposited On:26 Jan 2022 15:48

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