Formation mechanisms of hollow manganese hexacyanoferrate particles and construction of a multiple-shell structure

Abstract

Formation mechanisms of hollow manganese hexacyanoferrate (Mn-HCF) particles have been investigated. Mn-HCF particles, which were precipitated by mixing an aqueous solution of K₃[Fe(CN)₆] with MnCl₂ in the presence of sodium citrate, could be converted into a hollow structure just by washing with distilled water. The powder X-ray diffractometry suggested that the as-prepared particle has a core/shell morphology with different crystal structures: cubic-core and monoclinic-shell. The time evolutions of the particle size and shell thickness indicated that the core was rapidly (but not instantaneously) formed at the initial stage of the precipitation process, followed by a slower shell growth. In addition, the solubility of the cubic core was estimated to be about 2.5 times higher than that of the monoclinic shell, resulting in the preferential dissolution of the interior of the particle by the washing process. The formation procedure has been used to construct multiple-shell hollow Mn-HCF particles containing up to quadruple separated nesting shells by associating an additional growth technique.