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

摘要

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 ~(57)Fe M?ssbauer 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 ~(57)Fe M?ssbauer 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.