The structure and stability of CaFe layered double hydroxides with various Ca:Fe ratios studied by Mossbauer spectroscopy, X-ray diffractometry and microscopic analysis

The effects of the Ca(II)/Fe(III) ratios on the structure and Fe microenvironments have been studied in layered double hydroxides comprising of Ca(II) and Fe(III) (CaFe-LDH) prepared by the co-precipitation method. The Ca(II)/Fe(III) ratios were varied systematically from 2 to 6 and for characterisation Fe-57 Mossbauer spectroscopy, powder X-ray diffractometry and scanning electron microscopy were applied. XRD patterns of the samples at all Ca(II)/Fe(III) ratios exhibited reflections corresponding to CaFe-LDH and Fe-57 Mossbauer measurements revealed that Fe(III) was in a high-spin, somewhat disordered octahedral environment. Above the Ca(II)/Fe(III) ratio of 2 the reflections of Ca(OH)(2) also appeared. This phase was found to stabilise the LDH phase, while the phase-pure LDH decomposed on ageing. (C) 2012 Elsevier B.V. All rights reserved.