Inorganic Dendrites

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Science  14 Oct 2005:
Vol. 310, Issue 5746, pp. 197
DOI: 10.1126/science.310.5746.197a

Manganese oxides are used in batteries, chemical separation, and catalysis because of their porosity, acidity, and ion exchange properties. Organic templates have been used to make complex architectures but require subsequent purification of the end product with the risk of residual organic material remaining as impurities. Manganese oxides have previously been fabricated into octahedral molecular sieves that possess microporous tunnel structures, but the particles have not possessed uniform shapes or any sort of three-dimensional ordering. Yuan et al. have now developed a synthesis protocol that mixes potassium dichromate and manganese sulfate monohydrate under mild hydrothermal conditions to generate defined three-dimensional structures. Control of the resulting structures is achieved solely by varying the autoclave temperature from 120° to 180°C. Smaller crystals form at the higher temperature, creating a dendritic structure with finer and denser needlelike branches. The key to the control comes from the fact that the redox potential of Cr2O7,2−/Cr3+ is only slightly larger than that of Mn4+/Mn2+, so that the reaction is slow. This gives precise control over the nucleation and growth processes leading to highly uniform dendritic structures. — MSL

J. Am. Chem. Soc. 10.1021/ja053463j (2005).

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