Cobalt-iron hydroxycarbonates and their evolution to mixed oxides with spinel structure

Cobalt(II)-iron(III) mixed hydroxides with hydrotalcite-like structure have been synthesized. Depending on the experimental conditions during synthesis, Co-II becomes partially oxidized to Co-III. The solids have been characterized by X-ray diffraction, FTIR spectroscopy, temperature-programmed reduction and nitrogen adsorption at low temperature for specific surface area assessment. Reduction of Fe-III takes place at lower temperatures than that of bulk Fe3O4. Thermal treatment in air leads to oxidation of Co-II to Co-III, in the same temperature range where collapsing of the layered structure by decarbonation is observed. The nature of the spinel phases formed upon calcination at high temperature depends both on the calcination temperature and the calcination time.