Three‐Dimensional Magnesia‐Based Nanocrystal Assemblies Via Low‐Temperature Magnesiothermic Reaction of Diatom Microshells

Abstract

A low‐temperature (≤700°C) magnesiothermic reaction has been used for the first time to convert three‐dimensional (3‐D) silica‐based diatom microshells into nanocrystalline magnesia‐based replicas. Exposure of diatom microshells to Mg( g ) at only 650°–700°C resulted in the initial (direct) formation of MgO and Si nanocrystals (≤5 nm), that is, no intermediate magnesium silicate compounds were detected. Further reaction of Si with Mg( g ) led to the formation of Mg 2 Si, and then a Mg–Si liquid that sweated away to yield free‐standing, nanocrystalline MgO‐based replicas. Such direct low‐temperature magnesiothermic conversion of diatom microshells enables the synthesis of large numbers of 3‐D nanocrystal assemblies with well‐controlled morphologies for catalytic/chemical, biological, optical, and other applications.