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
Full content URL: https://doi.org/10.1021/jp051211z
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Item Type: | Article |
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Item Status: | Live Archive |
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 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 |
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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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