Synthesis and characterization of Mn–FeOx aerogels with magnetic properties

In an adaptation of sol–gel methods recently described for preparing iron oxide (FeOx) aerogels, we use epichlorohydrin as a proton scavenger to generate mixed metal oxides from ethanol solutions of Mn- and Fe-chloride salts. This reaction forms monolithic gels, which can be processed with supercritical CO2 extraction to form high-surface-area, highly porous Mn–FeOx aerogels. The amorphous as-prepared Mn–FeOx aerogel is transformed into a nanocrystalline form by heating in argon to 300 °C. Elemental analysis shows that a Fe:Mn ratio of 2:1 is attained, and the X-ray diffraction pattern for the nanocrystalline aerogel is consistent with that for spinel MnFe2O4, confirming that Mn(II) from the initial sol–gel mixture is incorporated into the crystal structure of the resulting oxide. The nanocrystalline Mn–FeOx aerogel exhibits magnetic properties consistent with a superparamagnetic material, while still retaining the characteristic morphology of an aerogel nanoarchitecture.