Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures

We have developed crystalline nanoarchitectures of iron oxide that exhibit superpararnagne behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous. high-surface-area loan. by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerocals into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment lamp temerature and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe3O4 (magnetite) or gamma-Fe2O3 (maghemite) phases, as verified by electron microscopy, X-ray am electron. diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution oil the Raman-active bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe3O4 and gamma-Fe2O3 components. which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)) through-connected porosity concentrated in the mesopore size range (2-50 rim), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured material with effective control of the pore-solid architecture, the nanocrystalline phase. and subsequent magnetic properties.