A procedure to obtain monodisperse nanoparticles of cobalt(II)
hexacyanoferrate(III) was investigated. To prevent a reaction with
[Fe(CN)6]3–, Co2+ was stored
in the form of a citrate complex at pH 7.8. By lowering the pH to
3.4 by the addition of acid, part of the Co2+ was released
and reacted with [Fe(CN)6]3– to form
nuclei, followed by their growth via mass-transfer of Co2+ from the citrate complex to the solid. Here, gelatin was employed
as a protective colloid. The particles obtained were cubic and fairly
monodisperse. The mean particle size was typically 160 nm and varied
from 30 to 450 nm, depending on the reactant contents. The formation
mechanism associated with equilibrium shifts was supported by a calculated
estimation of free Co2+ on the basis of the equilibrium
relationships involved in the preparation system.
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