Soft Chemical Design of Transition-Metal-Oxide/Clay Layered Nanocomposites
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The authors have developed a new oxidation method with using NaC10 as the oxidative
reagent. Here, the structure of the product will be examined by XRD associated with onedimensional Fourier analysis as well as magnetic susceptibility measurement. The structure determined was found to be essentially the same for Co, Ni and Mn species. Thus we will mainly describe on the case of Co, then the other cases will be mentioned as well. PROCESSING The cobalt hydroxide intercalated smectite compounds were prepared by the titration method [2,3,4]. Sodium fluoride tetrasilicic mica of 2.0 g ( Somacif provided by Coop Chemical Co. Ltd.; ideal chemical formula: Na 2Si8 Mg5 F4OanH 20; Chemcal analysis data: SiO 2 58.73%; MgO 27.58%; Na 2O 4.96%; F 8.02%; CaO 0.16%; Fe 20 3 0.07%; A120 3 0.48%; CEC: 115meq/100g-clay ) was dispersed into 150 ml of 0.1 M CoC12 aqueous solution. 300 ml of 0.1 M NaOH aqueous solution was added slowly with a drop rate of 1 ml/hour. The titration was carried out under nitrogen flow to avoid formation of cobalt carbonate throughout the procedure. The obtained powder was rinsed with 0.01 N HCI aqueous solution to remove the excess Co(OH) 2 precipitated on the outer surface of the clay and further washed with deionized water. The oxidation was performed in aqueous suspension system at room temperature. About 1.0 g of the cobalt hydroxide intercalation compound prepared above was dispersed in 50 ml of 1.5 M NaCIO aqueous solution and was vigorously stirred. The color of the 441 Mat. Res. Soc. Symp. Proc. Vol. 581 ©2000 Materials Research Society
sample immediately turned from original light pink to black, indicating the oxidation of cobalt hydroxide into electronically conductive phase. For equilibrium, the suspension was further stirred for 24 hours. The powder sample was washed with deionized water and separated centrifugally, then dried in vacuo at 313 K.
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STRUCTURAL STUDY 0
The first change via the oxidation was observed in the basal spacing of the sample. The XRD patterns were recorded
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Figure 1. Powder x-ray diffraction patterns for Co
on a rotating-anode type high power X-ray hydroxide / fluoride teterasilicic mica intercalation diffractometer, Rigaku RINT-2000 with compounds before and after oxidation. The monochlomated Cu Kct radiation in step numbers presented on the lines stand for the index scan measuring mode of a 0.02' step in 20. I of (001) reflections. The intensities of 001 reflections were The determined by film technique. powder XRD patterns as well as possible indices for the samples before and after oxidation are compared in Fig. 1. From the results, it is clear that the basal spacing expands from 1.48 to 1.96 nm via oxidation. The pattern of the before oxidation sample was quite similar to that reported by Ohtsuka et.al [2]. For the after oxidation sample, in the figure, at least 16 basal reflections can be distinguished from the noise level. The observed
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