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

Tao Zhang,Mira Ristić,Xuning Li,Gongquan Sun,Svetozar Musić,Marija Perović,Bratislav Antić,Ivana Mitar,Luhua Jiang,Junhu Wang,Marko Bošković,Chuchu Wu

doi:10.5562/cca3402

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, tetramethyl¬ammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni- doped goethite nanorods at 400 °C. The Ni2+- for-Fe3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe3+ and Ni2+) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe3+ and Ni2+) using Mossbauer 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 Ni2+-for-Fe3+ 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.

Highlights

The XRPD patterns of the samples Ni0 to Ni50 are shown in Figure 2, along with the positions and intensities of diffraction lines of goethite (α-FeOOH) given in the ICDD PDF card No 29-0713
XRPD patterns of the samples with 10 mol % Ni or higher indicate the presence of small amounts of Ni ferrite (NiFe2O4, ICDD PDF card No 54-0964) as an additional phase in these samples
Ni-doped goethite nanorods of good uniformity were synthesized by hydrothermal precipitation in the presence of tetramethylammonium hydroxide

Summary

Introduction

Cations into its crystal structure (Figure 1a) by substitution for Fe3+ ions at octahedral sites.[1] The M-for-Fe substitution can significantly change the properties of goethite. Nidoped goethite (with up to 4 mol % Ni) is a major component of nickel laterite ores (the most important source of nickel).[16,17,18,19] Incorporation of Ni in synthetic goethite has been reported in several publications.[20,21,22,23,24] Ni2+-for-Fe3+ substitution in goethite was confirmed by determination of a slight increase in unit cell volume due the different ionic radii of Ni2+ (0.69 Å) and Fe3+ (0.645 Å).[25] Substitution increases with increased Ni content in the initial precursor and is higher in the surface layer of Nidoped goethite particles than in the inner layers.[21,22] Ni doping in goethite causes a decrease in the hyperfine

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Conclusion