Characterization of mixed Fe-Al oxyhydroxides and oxides obtained by hydrothermal synthesis of nitrates, chlorides and urea as precursors

Abstract

Materials based on mixed aluminum and iron (III) and oxyhydroxides were prepared by the hydrothermal synthesis using urea, nitrates, or chlorides salts in different Al³⁺:Fe³⁺ molar ratios. The structural, morphological, and thermal properties of the materials were evaluated. The mixtures of Al³⁺ and Fe³⁺ nitrates led to the formation of hematite whereas, for the materials obtained from chlorides, different crystalline phases of Fe³⁺ were identified. For the thermal behavior, it was observed that, regardless of the anion of the precursors’ salts, the samples with composition 30%:70% (Al³⁺:Fe³⁺) stood out from the others. After calcination, the hematite phase was identified in all samples. The precursor salts and the Al³⁺:Fe³⁺ ratios reflected in differences between the samples in the evaluated properties. From the observed results, the occurrence of isomorphic substitutions of Fe³⁺ by Al³⁺ in the hematite phase was observed, which provided changes in the evaluated properties in relation to the material without the presence of Al³⁺.

Keywords:
hydrothermal synthesis; aluminum; iron; mixed oxyhydroxides; mixed oxides