Synthesis of Nano-Dimensional Iron–Cobalt Spinel Mixed Oxides from Layered-Type Carbonate Hydroxide Precursors

Pyroaurite-like carbonate hydroxide precursors Co1−xFex(CO3)x/2(OH)2·nH2O, where x varies in the range 0.25 ≤ x ≤ 0.75, yield cation deficient mixed oxides with particle dimensions in the nano-scale range. The thermal decomposition and spinel structure formation processes have been studied by thermal analysis and IR spectroscopy, revealing an intermediate of hydroxide oxide type. Mesoporous mixed oxides with cubic spinel structure were synthesised at 300—400 °C with significant contribution of small pores of radii <200 A. Oxygen desorption from cobalt ferrite, synthesised at 350 °C, suggests the existence of a high content of extraframework oxygen. The temperature-programmed reduction (TPR) with hydrogen occurs in one stage for all cobalt/iron compositions. The peak maxima shift to higher temperatures and a broadening is observed with increasing the iron content. Partly inverse cation distributions of the spinel ferrites are deduced from the Moessbauer spectra.

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