Strong Akaganeite Aerogel Monoliths Using Epoxides:  Synthesis and Characterization

Abstract

The synthesis of iron(III) oxide aerogel monoliths was performed by adding any one of several different 1,2- and 1,3-epoxides to ethanolic Fe(III) salt solutions at room temperature. While all of the epoxides examined resulted in gel formation, robust low-density (∼30−40 kg/m3; 99% porous), high-surface-area (∼250−300 m2/g), aerogel monoliths were prepared by the addition of 1,3-epoxide derivatives to solutions of FeCl3·6H2O, followed by drying with supercritical CO2. Both types of iron(III) oxide aerogels (those made with 1,2- and 1,3-epoxides respectively) were characterized using elemental analysis, X-ray diffraction, thermal analysis, acoustic measurements, transmission electron microscopy, scanning electron microscopy, and N2 adsorption desorption analysis. Elemental analyses and powder X-ray diffraction indicated that the strong aerogel monoliths made with the 1,3-epoxides are made up predominately of polycrystalline β-FeOOH, akaganeite, and those made with the 1,2-epoxides are amorphous. To our knowledge, this is first known report of synthesis and characterization of akaganeite aerogel materials. Transmission electron microscopy analysis indicates that aerogels derived using 1,3-epoxides have a microstructure made up of a highly reticulated network of fibers with diameters from ∼5 to 35 nm and lengths several times that, whereas those resulting from the use of 1,2-epoxides consist of interconnected spherical particles, whose diameters are 5−15 nm. The difference in microstructure results in each type of aerogel displaying very distinct physical and mechanical properties. In particular, the stiffness of the β-FeOOH aerogels is remarkable for a transition metal oxide aerogel. Monolithic cylinders of β-FeOOH aerogel can be sintered at 515 °C, transforming to α-Fe2O3 without shattering.

Structure of Low-Density Nanoporous Dielectrics Revealed by Low-Vacuum Electron Microscopy and Small-Angle X-ray Scattering

“…18) and β-FeOOH (Ref. 19). Interestingly, the exterior surfaces of all these AGs (i.e., the monolith skin layers) contain cracks, which are not observed in images of cross-sections.…”

Iron oxyhydroxide aerogels and xerogels by controlled hydrolysis of FeCl3·6H2O in organic solvents: stages of formation

“…trimethylene oxide) has also been reported. 21 The syntheses of xero-and aerogels are similar, except the very nal step, the removal of solvents aer gelation. For obtaining aerogels, supercritical CO 2 extraction should be applied 8,22 otherwise dense xerogels form.…”

Sources X : du multi-keV-ns au multi-MeV-ps

“…La première d'entre elles consiste à se servir de cibles solides initialement sous-denses, constituées d'aérogels à dopant métallique [1,2] ou d'oxydes métalliques [3]. Une seconde voie est d'utiliser une partie, si possible faible, de l'énergie laser disponible pour créer un plasma sous-dense.…”

“…Le laser ionise la cible et génère des électrons suprathermiques de plusieurs dizaines de keV. Ces électrons 01007-p. 3 …”