The effect of the starting solution on the physico-chemical properties of zinc ferrite synthesized at low temperature

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Abstract

Fine particle zinc ferrite powders (ZnFe2O4) were synthesized by co-precipitation of a bi-ionic Fe3+/Zn2+ solution with 1 M n-butylamine at low temperature. Ferric nitrate and ferrous sulphate solutions were used as the starting material to investigate the effect of the source of iron on particle size, morphology, thermal behaviour and surface area of the final products. ZnFe2O4. In both cases, Zn2+ ions were provided by ZnO. The ferrous ions of the sulphate solution were previously oxidized with H2O2 in sulphuric medium. The cubic spinel-type structure of the ferrite product was obtained at a lower temperature when nitrate solution was used. Zinc ferrite of smaller particle size and higher surface area was obtained when ferrous sulphate was used as the starting solution. The ferrite precursors produced at room temperature and final products were characterized by X-ray powder diffraction, Fourier transformed infrared spectroscopy, thermal analyses, scanning and transmission electron microscopy and nitrogen adsorption volumetry.

Introduction

Ferrite spinels may be described by the general formula MFe2O4, where M is a divalent cation. The unit cell contains eight formula units and is usually referred to as space group Fd3m (Oh7) with cations occupying special positions 8a and 16d. The ideal structure consists of cubic close packing of oxygen atoms (32e) in which one-eighth of the tetrahedral and half of the octahedral interstices are occupied. In the case of zinc ferrite, Zn2+ cations occupy the tetrahedral sites and Fe3+ cations the octahedral sites in ZnFe2O4 as in a ‘normal’ spinel [1], [2].

Zinc ferrite, like all spinel-type materials, is rather sensitive to conditions of synthesis, which may affect its morphological and structural properties. When the spinel is synthesised at low temperature, highly reactive materials of small particle size and high surface area are produced [3], [4]. These materials play an important role in many industrial applications such catalysis, photocatalysis and adsorption [5], [6], [7] and pigment technologies [8], [9]. Most applications are extremely sensitive to the surface-related properties of ferrites. Traditionally, the ceramic method involving very high reaction temperatures was used for their synthesis. In contrast, current research efforts are focused towards the development of low temperature synthesis methods in order to prepare materials of easily designed and controlled surface area and particle size [10], [11], [12], [13], [14].

Recently, a pure and nanocrystalline zinc ferrite spinel, ZnFe2O4, was obtained, by the present authors, from a steel industry wastewater [15]. The low temperature method employed consisted of the co-precipitation of Zn2+ and Fe3+ cations at a molar ratio of Zn2+/Fe3+=1/2 using a 1 M solution of n-butylamine up to pH 10.5. This method allowed the total recovery of the iron content from the industrial waste as zinc ferrite, a material of highly added value.

The present investigation describes the application of the above procedure to the synthesis of ZnFe2O4 spinel-type material from different ferric solutions. Evaluation was made of the effect of the starting solution on the physical and chemical characteristics of the ferrite. Zinc ferrite was prepared from Fe(NO3)3·9H2O or FeSO4·7H2O (oxidised with H2O2 in sulphuric medium) solutions. The results were compared to those obtained using industrial wastewater as the starting material [15].

Section snippets

Synthesis

Reagent grade Fe(NO3)3·9H2O and FeSO4·7H2O were dissolved separately in distilled water (200 ml) to obtain 0.07 mol iron solutions. The ferrous iron of the sulphate solution was oxidised to ferric iron by the addition of H2O2 in sulphuric medium. Solutions containing Fe3+ and Zn2+ were prepared by the addition of ZnO at a constant molar ratio Fe3+/Zn2+ of 2.0. The resulting solutions were, then gelified by slow addition (1 ml min−1) of 1 M n-butylamine solution with a continuous and vigorous

Precursor characterisation and spinel-phase formation

Fig. 1 shows the X-ray powder diffraction pattern recorded for the product obtained from ferric nitrate solution, hereafter named nitrate precursor. The XRD pattern obtained was consistent with that of a ‘two lines’ ferrihydrite [3]. Only two, very broad diffraction bands may be seen at 2.55 and 1.51 Å. The high temperature heating chamber was used to determine the thermal evolution of the precursor at temperatures up to 1100°C. The XRD patterns of samples obtained at different temperatures are

Conclusions

Small crystallites of zinc ferrite ZnFe2O4 were synthesised using a low temperature method. Ferrite precursors were obtained by the co-precipitation of zinc and iron cations from solutions with molar ratio Fe3+/Zn2+=2.0, using a 1 M aqueous solution of n-butylamine as the precipitation agent. The iron compounds were obtained from two different sources, ferric nitrate and ferrous sulphate, to evaluate the effect on the physico-chemical properties of the zinc ferrite obtained. Precursors of zinc

References (16)

  • J.J. Liu et al.

    Mater. Res. Bull.

    (1996)
  • X. Li et al.

    J. Alloys Compd.

    (1996)
  • J.L. Martı́n De Vidales et al.

    Mater. Res. Bull.

    (1994)
  • F.A. López et al.

    J. Alloys Compd.

    (1998)
  • R.J. Hill et al.

    Phys. Chem. Miner.

    (1979)
  • T. Kamillama et al.

    Solid State Commun.

    (1992)
  • M. Ueda et al.

    J. Mater. Chem.

    (1993)
  • T. Sato et al.

    Appl. Phys.

    (1990)
There are more references available in the full text version of this article.

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