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A resonance Raman spectroscopic study of the protonation of Disperse Orange 25 in solution and adsorbed on oxide surfaces
Author(s) -
Dines Trevor J.,
MacGregor Louise D.,
Rochester Colin H.
Publication year - 2007
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1710
Subject(s) - protonation , raman spectroscopy , chemistry , adsorption , molecule , oxide , aqueous solution , resonance (particle physics) , photochemistry , analytical chemistry (journal) , inorganic chemistry , organic chemistry , atomic physics , ion , physics , optics
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 SiO 2 surface, but its adsorption on SiO 2 Al 2 O 3 or H‐mordenite results in protonation. This observation indicates the presence of Brønsted acidic sites on these oxide surfaces with p K a 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.