Issue 27, 2013

pH-dependent electronic surface spectra of chromophore species in the charged silica–water interface

Abstract

The structure of the pH-dependent silica–water interface has been probed with two charged counter-ion chromophores Crystal Violet (CV) and Malachite Green (MG) by evanescent wave cavity ring-down electronic spectroscopy. The electronic spectra of these species in the charged interface have been measured directly over the wavelength range 570–680 nm. The effective CV interfacial counter-ion concentration is 185-fold larger than the bulk with a fully charged silica surface at pH 9, corresponding to a surface concentration of 0.26 molecules nm−2. The chromophoresilica surface association and dissociation kinetics indicate a binding energy at pH 9 >28 kJ mol−1 for each chromophore: a loosely bound molecular layer. The electronic spectrum of CV in the interface shows two maxima: one feature is blue-shifted 2 nm from the solution-phase maximum at 583 nm, and the second feature is red-shifted 24 nm. A Lorentzian deconstruction of the spectra indicates that they are consistent with two molecular environments: one closely associated with the surface sharing delocalised electrons and a second confined to the interface but randomly oriented.

Graphical abstract: pH-dependent electronic surface spectra of chromophore species in the charged silica–water interface

Article information

Article type
Paper
Submitted
22 Feb 2013
Accepted
10 May 2013
First published
10 May 2013

RSC Adv., 2013,3, 10927-10933

pH-dependent electronic surface spectra of chromophore species in the charged silica–water interface

N. D. L. Walker, R. V. Olkhov and A. M. Shaw, RSC Adv., 2013, 3, 10927 DOI: 10.1039/C3RA40925B

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