Characterisation of cobalt-zinc hydroxycarbonates and their products of decomposition

A series of cobalt-zinc hydroxycarbonate precursors with nominal Co/Zn atomic ratios of 0/100, 10/90, 20/80, 30/70, 40/60, 50/50, 70/30, 90/10 and 100/0 have been synthesized from their mixed metal nitrates and ammonium carbonate by a coprecipitation route. X-Ray and electron diffraction studies of the precursors revealed that hydrozincite, Zn-5(CO3)(2)(OH)(6), was the major phase at Co/Zn ratios less than or equal to 30/70 and spherocobaltite, Co(CO3), predominated at Co/Zn ratios of 50/50 to 90/10. The Co/Zn 100/0 precursor formed only the metastable basic carbonate Co(CO3)(0.5)(OH)(1.0). 0.1H(2)O. UV-VIS-NIR diffuse reflectance spectroscopy revealed that the cobalt was present in the 2+ oxidation state in an octahedral environment in all the precursors. Decomposition of the Co/Zn precursors at 350 degrees C resulted in the formation of ZnO as the major phase at low Co loadings and Co3O4 as the major phase at high loadings. The highest surface areas were attained from the decomposition of basic cobalt carbonate or spherocobaltite containing little or no zinc in solid solution. XPS studies of the oxides revealed that only Co3+ and Zn2+ ions were present at the surface at Co/Zn ratios less than or equal to 30/70 indicating the presence of the 'surface spinel', ZnCo2O4. Co2+ was detected at higher Co loadings.