Sol–gel synthesis of zinc ferrite-based xerogel monoliths with well-defined macropores

Abstract

Starting from an aqueous solution, porous zinc ferrite-based xerogel monoliths have been prepared via a sol–gel route accompanied by phase separation mediated by propylene oxide in the presence of poly(acrylamide). The xerogels possess well-defined macropores, and the macroporous morphologies could be easily controlled (macropore size ranges from 0.55 to 1.29 μm) by simply changing the starting composition. As-dried xerogel samples were amorphous under X-ray diffraction, while heat-treatment in air brought about the formation of spinel type ferrite phase, ZnFe₂O₄. Calcination under Ar atmosphere allowed the crystallization of various iron-based phases/carbon composites (Fe₃O₄, Fe_1-δO, Fe₃N, Fe₄N, Fe₃C, and Fe). Samples heated under Ar flow exhibited hierarchical pore structures, including continuous macropores, in addition to mesopores and micropores embedded in the carbon-containing composite matrices.