Iron(III) Oxide Nanoparticles in the Thermally Induced Oxidative Decomposition of Prussian Blue, Fe₄[Fe(CN)₆]₃

Abstract

The thermally induced decomposition of Prussian Blue, Fe 4 [Fe(CN) 6 ] 3 (PB), was studied in air at 250 and 350 °C. Amorphous Fe 2 O 3 nanoparticles, cubic bixbyite β- and cubic spinel γ-Fe 2 O 3 (maghemite) polymorphs, have been identified as the products of the decomposition under different reaction conditions. 57 Fe Mössbauer spectroscopy, XRD, AFM, TEM, quasielastic light scattering method (QELS) of particle size analysis, BET surface area, and magnetization measurements were used to understand the influence of the PB particle size and oxidation conditions on the decomposition mechanism at 250 and 350 °C. At a minimum decomposition temperature of 250 °C, amorphous Fe 2 O 3 nanoparticles were formed with the size ranging from 1 to 4 nm and large surface area of 400−200 m 2 /g in dependence on the PB particle size. Such small amorphous Fe 2 O 3 nanoparticles were obtained by the solid-state route for the first time. At 350 °C, cubic β-Fe 2 O 3 and γ-Fe 2 O 3 polymorphs were identified and their contents were found to be strongly dependent on the initial PB particle size and oxidation−diffusion conditions. Generally, the higher relative content of γ-Fe 2 O 3 was obtained for larger PB particles and in air-limited conditions.