Synthesis of Monolithic Hierarchically Porous Iron-Based Xerogels from Iron(III) Salts via an Epoxide-Mediated Sol–Gel Process

Abstract

Various iron-based polycrystalline monoliths, Fe3O4, iron, and Fe3C, with hierarchically distributed pores have been synthesized from ionic precursors using a sol–gel process accompanied by phase separation. Propylene oxide acts as a proton scavenger to increase pH moderately and uniformly in a reaction solution, which leads to homogeneous gelation. On the other hand, poly(acrylamide) works as a phase separation inducer as well as a precipitation inhibitor. Appropriate choice of iron precursor, solvent, polymer, and epoxide allowed the formation of iron(III)-based xerogels with cocontinuous macroporous structures. The dried gels were amorphous, whereas heating in air above 300 °C led to the formation of α-Fe2O3. Calcination under an inert condition above 400 °C formed Fe3O4, iron, and Fe3C without collapse of macrostructures. Examination has been carried out using SEM, TG-DTA, FT-IR, Hg intrusion, pH measurement, X-ray diffraction, and N2 adsorption–desorption.