Hydrothermal precipitation of β-FeOOH nanostructure(s) in mixed solvent: study of their morphological and structural evolution

This paper describes the homogeneous precipitation of β-FeOOH nanorods (±5 nm dia.) in alcohol—water mixed solvents. Four alcohols, butanol (BuOH), propanol (PrOH), ethanol (EtOH) and methanol (MeOH), were mixed with water as the solvents to evaluate the effect of alcohols on the β-FeOOH particle characteristics under different hydrothermal process parameters. Crystal splitting was achieved at 0.7 M [FeCl₃] in BuOH, and β-FeOOH nanoribbons were obtained in MeOH. Replacing Cl− with SO₄ ²⁻ in a controlled pH (2) environment results a 98 % reduction in the synthesis time of hydronium iron jarosite, H₃O.Fe₃(SO₄)₂(OH)₆, regardless of the nature of the alcohol. Single phase hydronium iron jarosite could not be synthesised without the presence of alcohol. Alcohol-to-water ratio played a critical role in controlling particle nucleation and growth. Spherical α-Fe₂O₃ (haematite) was obtained in pure alcohol, whereas an addition of 2 % (v/v) alcohol resulted in the precipitation of β-FeOOH nanofibrillar. Nanosize spherical α-Fe₂O₃ (average dia. 95 ± 19 nm) was achieved by altering solution pH in selective solvent. Required temperature for β-FeOOH to α-Fe₂O₃ transformation is solvent dependent and increases with the increasing carbon chain length in the linear alkyl chain of the solvent. The choice of solvent did not affect the Raman spectrum of the synthesised sample when compared to the standard Raman peaks. The synthesised β-FeOOH nanorods do not show ferromagnetism at any temperature down to 4 K and have a magnetic moment per unit mass of 1–1.5 Am²/kg at 5T.