A resonance Raman spectroscopic study of the protonation of Disperse Orange 25 in solution and adsorbed on oxide surfaces

The protonation of Disperse Orange 25 (DO25) in aqueous solution, and upon adsorption on oxide surfaces, was studied by resonance Raman (RR) spectroscopy. The neutral and protonated forms of DO25 were modelled by DFT calculations of the isolated molecules in the gas phase at the B3‐LYP/DZ level, ena...

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Bibliographic Details
Published in:Journal of Raman spectroscopy 2007-07, Vol.38 (7), p.832-840
Main Authors: Dines, Trevor J., MacGregor, Louise D., Rochester, Colin H.
Format: Article
Language:English
Subjects:
Adsorption
DFT calculations
Disperse
Mathematical models
Oranges
Oxides
Protonation
resonance Raman spectroscopy
Spectroscopy
surface acidity
Surface chemistry
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Summary:The protonation of Disperse Orange 25 (DO25) in aqueous solution, and upon adsorption on oxide surfaces, was studied by resonance Raman (RR) spectroscopy. The neutral and protonated forms of DO25 were modelled by DFT calculations of the isolated molecules in the gas phase at the B3‐LYP/DZ level, enabling calculation of the vibrational spectra of these species, together with vibrational assignments. RR spectra show that DO25 is physisorbed on the SiO2 surface, but its adsorption on SiO2Al2O3 or H‐mordenite results in protonation. This observation indicates the presence of Brønsted acidic sites on these oxide surfaces with pKa values ⩽2.5. RR studies of the adsorption of DO25 can therefore provide useful information on the nature of surface acidity on oxides, which is complementary to that obtained from other probe molecules. Copyright © 2007 John Wiley & Sons, Ltd.
ISSN:0377-0486
1097-4555
DOI:10.1002/jrs.1710