Co hydroxide polymorphs (green alpha-Co(OH)(2), red beta-Co(OH)(2) and brown beta-Co(OH)(3)) formed at separate positions in a test-tube. Diffusion of hydrazine hydrate downward in agar gel facilitated the reaction between hydrazine and Co2+ leading a dilatational wave of reactant concentration. The resulting periodic Liesegang bands of alpha-Co(OH)(2) were observed due to the diffusion hindrance of reactants. It can be deduced that the high concentration of Co2+ causes formation of alpha-Co(OH)(2) while the low concentrations produce beta-Co(OH)(2 center dot)beta-Co(OH)(2) is oxidized readily to form brown beta-Co(OH)(3) at the upper area of agar gel with high alkali condition and O-2 distribution. This study is helpful to learn the formation of more than one product and prepare multiple materials in single chemical reaction system. In addition, the obtained alpha-Co(OH)(2) has been stabilized in the gel medium for at least 3 months. It may facilitate its application in many areas especially in electrochemical area since alpha-Co(OH)(2) typically exhibits higher conductivity and electrocatalysis than beta-Co(OH)(2) while in the past its application often is limited by thermodynamically instability. (C) 2019 Elsevier B.V. All rights reserved.
[1]Univ Shanghai Sci & Technol, Inst Bismuth Sci, Shanghai 200093, Peoples R China.
[2]Shanghai Univ Med & Hlth Sci, Shanghai Key Lab Mol Imaging, Shanghai 201318, Peoples R China.
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