Influence of Al3+ ions on the direct hydrothermal formation and properties of hematite (α-Fe2O3) nanorods

Aluminium can often be found in natural hematite (α-Fe2O3) where it partially replaces iron, while a partial Al-for-Fe substitution in synthetic hematite can greatly affect its properties and performances in different applications. In this work, the influence of Al3+ ions on the hydrothermal formation of hematite nanorods, as well as on different properties and photocatalytic activity of the obtained Al-doped hematite nanoparticles, was investigated. A direct hydrothermal method with iron(III) chloride and 1,2-diaminopropane was used for the synthesis of uniform hematite nanorods. The influence of the presence of various molar fractions of Al3+ ions during this hydrothermal process on the formation mechanism and physico-chemical properties (structural, morphological, vibrational, optical, electrical, magnetic) of obtained hematite nanoparticles was investigated. The presence of Al3+ ions in the reaction mixture prevented the formation of goethite phase during the hydrothermal synthesis of hematite. A gradual change in the shape of the formed hematite particles from long and thin hexagonal nanorods to shorter and thicker hexagonal nanorods, nanoprisms and nanoplates with increased molar fractions of Al3+ ions was observed. Incorporation of Al3+ ions into the crystal structure of hematite by Al3+-for-Fe3+ substitution caused a gradual decrease in the unit cell size, hyperfine magnetic field, Morin transition temperature and electrical conductivity, as well as a gradual increase in the crystallite size and optical band gap. Significant changes in magnetic and vibrational properties were also observed. Prepared samples were evaluated as photocatalysts for the degradation of RhB dye by the heterogeneous photo-Fenton process and very good photocatalytic activities of all samples (pure and doped) were observed.