Surface analysis of magnetite nanoparticles in cyclohexane solutions of oleic acid and oleylamine

The surface of magnetite (Fe 3O 4, d = 6.3 ± 0.7  nm) nanoparticles dispersed in cyclohexane was studied in the presence of oleic acid and oleylamine using in situ FTIR spectroscopy. Equimolar mixtures of these surfactants are widely used in the chemical synthesis of nanoparticles with a low polydis...

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Bibliographic Details
Published in:Vibrational spectroscopy 2007-01, Vol.43 (1), p.243-248
Main Authors: Klokkenburg, M., Hilhorst, J., Erné, B.H.
Format: Article
Language:English
Subjects:
Adsorption
In situ FTIR
Magnetite
Nanoparticles
Oleic acid
Oleylamine
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Summary:The surface of magnetite (Fe 3O 4, d = 6.3 ± 0.7  nm) nanoparticles dispersed in cyclohexane was studied in the presence of oleic acid and oleylamine using in situ FTIR spectroscopy. Equimolar mixtures of these surfactants are widely used in the chemical synthesis of nanoparticles with a low polydispersity. Here, the IR spectra indicate that oleic acid molecules adsorb to the magnetite surface as a carboxylate. Measurements as a function of surfactant concentration yield an adsorption isotherm, with about two surfactant molecules adsorbed per nm 2 of magnetite at 1 mM surfactant concentration and about 3.5 molecules per nm 2 at 310 mM, of the order expected for full monolayer coverage. No spectral indication is found of oleylamine molecules at the surface of magnetite. In solution, however, almost every oleylamine molecule combines with an oleic acid molecule to form an acid–base complex, with an association constant of 3.5 × 1 0 4 dm 3 mol − 1 .
ISSN:0924-2031
1873-3697
DOI:10.1016/j.vibspec.2006.09.008