Synthesis and Properties of Ni-doped Goethite and Ni-doped Hematite Nanorods

Abstract

Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate solutions with various Ni/(Ni+Fe) ratios (0, 5, 10, 20, 33 and 50 mol % Ni) by hydrothermal precipitation in a highly alkaline medium using the strong organic alkali, tetramethylammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni-doped goethite nanorods at 400 °C. The Ni 2+ -for-Fe 3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe 3+ and Ni 2+ ) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe 3+ and Ni 2+ ) using Mössbauer spectroscopy. Single-phase goethite nanorods were found in samples containing 0 or 5 mol % Ni. A higher Ni content in the precipitation system (10 mol % or more) resulted in a higher Ni 2+ -for-Fe 3+ substitution in goethite, and larger Ni-doped goethite nanorods, though with the presence of low crystalline Ni-containing ferrihydrite and Ni ferrite (NiFe2O4) as additional phases. Significant changes in FT-IR and UV-Vis-NIR spectra of prepared samples were observed with increasing Ni content. Electrochemical measurements of samples showed a strong increase in oxygen evolution reaction (OER) electrocatalytic activity with increasing Ni content. © 2018 Croatian Chemical Society. All Rights Reserved.