title: Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures.
abstract: We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic 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 form, 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 aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) 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 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties.
authors.affiliation: Surface Chemistry (Code 6170) and Materials and Sensors (Code 6360) Branches, Naval Research Laboratory, Washington, D.C. 20375, USA. jwlong@ccs.nrl.navy.mil
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Long
authors.forename: Michael S
authors.initials: MS
authors.lastname: Logan
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Rhodes
authors.forename: Everett E
authors.initials: EE
authors.lastname: Carpenter
authors.forename: Rhonda M
authors.initials: RM
authors.lastname: Stroud
authors.forename: Debra R
authors.initials: DR
authors.lastname: Rolison