Synthesis and Characterization of Cobalt(II)-Iron(III) Hydroxide Carbonate, a Layered Double Hydroxide Belonging to the Pyroaurite Group
✍ Scribed by Hans Christian Bruun Hansen; Christian Bender Koch; Reginald Morton Taylor
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 775 KB
- Volume
- 113
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
A pure pyroaurite-type compound (PTC) with the composition (\left.\left[\mathrm{Co}{5.42}^{\mathrm{II}} \mathrm{Fe}{2.47}^{\text {III }}(\mathrm{OH}){16}\right]\left(\mathrm{CO}{3}\right){1.12} x \mathrm{H}{2} \mathrm{O}\right](x=5-6)) has been synthesized by air oxidation of (\mathrm{Fe}(\mathrm{II})) in a solution of (\mathrm{Co}\left(\mathrm{NO}{3}\right){2}) at (\mathrm{pH} 6.60) and has been characterized by powder (X)-ray diffraction, electron microscopy, Fourier transform infrared spectroscopy, Mössbauer spectroscopy, and differential thermal analysis. This reddishbrown compound consists of mostly hexagonally shaped crystals (diam. 0.1-0.4 (\boldsymbol{\mu \mathrm { m }}) ) apparently more or less intergrown and forming spherical aggregates (diam. 3-5 (\mu \mathrm{m}) ). The hexagonal unit-cell parameters are (a=0.312) and (c=2.278 \mathrm{~nm}), and there is an ordered stacking of consecutive hydroxide layers. On heating in a nitrogen atmosphere, two DTA endothermic peaks are observed at 195 and (260^{\circ} \mathrm{C}), respectively; the low-temperature peak is due to desorption of interlayer water, whereas decomposition of carbonate and dehydroxylation of the structure causes the high-temperature peak. Mössbauer parameters ( (\delta=0.35 \mathrm{~mm} \mathrm{~s}^{-1}) and (\Delta E_{Q}=0.49) (\mathrm{mm} \mathrm{s}{ }^{-1}) at (298 \mathrm{~K}) ) are consistent with ferric ions in the high spin state. From the IR spectrum, the (D_{3 h}) symmetry of the interlayer (\mathrm{CO}_{3}^{2-}) appears unperturbed. of 1994 ^eadenic Press, Irc.