Strategies for the synthesis of open vase-like microcapsule ordered arrays with transition metal oxyhydroxide walls...

This review outlines the basic principles of a chemical strategy for obtaining arrays of open vase-like microcapsules (VLMs) with walls made of metal oxyhydroxides on the surface of substrates. This strategy typically involves the following steps: synthesizing an array of homogeneous microcapsules on the surface of an aqueous alkali solution by spraying a metal salt solution, then removing excess reagents by rinsing the array with water and transferring it to a substrate. The conditions for the formation of such microcapsules and their arrays at various stages of the process are analyzed, and the conditions for obtaining VLM arrays with walls made from Ni_xFeOH, Mn₃O₄, Cu(OH)₂/CuO, CeO₂, and CeO₂:Eu_x nanocrystals are considered. The unique morphology of these open microcapsules is noted, as a rule, to possess a special rim around the hole serving as a kind of "foundation" when they are fixed to the substrate surface during the transfer stage. Attention is drawn to the possibility of using this approach to create VLMs with walls from a wide range of difficult-to-dissolve complex metal oxyhydroxides and their possible practical application as photonic materials, photothermal catalysts with the properties of "nano-greenhouses", various kinds of electrode materials for electrochemical energy and sensors, microreactors and micromotors, etc. The prospects for further development of this methodology are also outlined.