Elsevier

Superlattices and Microstructures

Volume 77, January 2015, Pages 134-151
Superlattices and Microstructures

Mg–Co–Zn magnetic nanoferrites: Characterization and their use for remediation of textile wastewater

https://doi.org/10.1016/j.spmi.2014.11.013Get rights and content

Highlights

  • Mg-doped Co–Zn ferrites synthesized using sol–gel auto combustion method.

  • Investigation of structural, magnetic and electrical properties of ferrites.

  • The applications of ferrites for the photo degradation of methyl orange dye.

  • Resistivity regularly decreased with temperature reflecting semiconductor behavior.

  • The photocatalytic degradation was enhanced with Mg ion increased from 0.2 to 1.0.

Abstract

Highly active and magnetically separable Mg substituted cobalt zinc nanoferrites having formula (Co0.6Zn0.4MgxFe2xO4, x = 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized using sol–gel auto combustion method. The photo-catalytic activity of all the nanoferrites samples annealed at 1000 °C under visible light was evaluated by the degradation of Methyl orange (MO) dye. All the heterogeneous catalysts were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction patterns and vibrating sample magnetometer. FT-IR absorption spectra exhibited two absorption bands in the range of 400–600 cm−1 which were characteristic feature of spinel ferrites. Powder X-ray diffraction patterns at room temperature confirmed the formation of single-phase cubic spinel (FCC) structure with Fd3m space group in all the nanoferrites. Lattice parameter was found to decrease from 8.390 to 8.360 Å with increase in Mg concentration. Semiconductor behavior of all the prepared samples was confirmed by performing electrical measurements. Saturation magnetization (Ms) was observed to decrease from 55.13 to 24.14 (emu/g) with increase in magnesium concentration. All the samples were catalytically active and photo catalytic efficiency was enhanced as the concentration of magnesium ion increased from 0.2 to 1.0. Complete degradation of the MO dye was achieved along with easy magnetic separation of the catalyst from the solution, thereby exhibiting its potential use in organic pollutant removal from wastewater.

Graphical abstract

Mechanism of photodegradation of methyl orange in the presence of prepared ferrites.

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Introduction

Magnetic nano spinel ferrites have grabbed attention due to their fascinating size dependent optical, electronic, magnetic, thermal, mechanical and chemical properties [1], [2]. The properties of such nano-structured materials are deeply influenced by their chemical composition and microstructure, which are sensitive to the manufacturing process [3]. Spinel ferrites have the general formula AFe2O4 (where A2+ = Co, Ni, Zn, Mg, etc.) and the unit cell contains 32 oxygen atoms in cubic close packing with 8 tetrahedral (Td) and 16 octahedral (Oh) occupied sites. By changing the type of divalent cation, it is possible to obtain a wide range of different physical and magnetic properties [4].

Magnesium subsituted Co–Zn ferrite is a mixed spinel in which tetrahedral, Td (A), sites are occupied by Zn2+ and Fe3+ ions and the octahedral, Oh (B), sites are occupied by Mg2+ and Fe3+ in the cubic spinel lattice [5]. Terrific work has been reported on magnetic and electrical properties of magnesium substituted ferrites [6], [7], [8], [9], [10], [11].

Ferrites have practical application in information storage systems, ferro-fluid technology, magneto-caloric refrigeration and magnetic diagnostics [12]. They can even act as catalyst under visible light for the degradation of dyes. In literature, various authors [13], [14], [15], [16] have reported degradation of different types of dyes in the presence of ferrites. Wei et al. [13] employed spherical bismuth ferrite (BiFeO3) microcrystals for degradation of rhodamine B under visible light. Sun et al. [14] synthesized sponge like ZnFe2O4 by solution combustion method and compared photocatalytic activity with ZnFe2O4 prepared by conventional solid state reaction. The sponge like ZnFe2O4 showed better photocatalytic activity for rhodamine B degradation under visible light. A study on magnetic property and photocatalytic activity for degradation of methyl orange dye in the presence of lanthanum ferrite (LaFeO3) and manganese substituted lanthanum ferrite (LaFe0.5Mn0.5O3) was carried out by Wei et al. [15]. The samples were ferromagnetic in nature and higher photocatalytic activity for substituted ferrite was observed as compared to pure lanthanum ferrite. 1-D ZnFe2O4 nanorods of diameter 100–200 nm were synthesized by Jia et al. [16]. The as prepared ZnFe2O4 nanorods exhibited good photocatalytic decomposition activity for methylene blue under solar light irradiation. Shen et al. [17] investigated the degradation of benzene on Mg-ferrite/hematite/PANI nanospheres and concluded that photo catalytic degradation of benzene was increased under visible-light irradiation. Borhan et al. [18] studied the effect of Al3+ substituted zinc ferrite on photo catalytic degradation of orange I azo dye and reported that the best performances were observed when the Al3+ and Fe3+ are presents in equimolar amounts. Borhan et al. [19] explored the photo catalytic activity of spinel ZnFe2−xCrxO4 nanoparticles on removal Orange I azo dye from aqueous solution. The authors concluded that dye removal efficiency was enhanced up to 92.8% for x = 1.50 composition when Cr3+ cations were introduced in octahedral lattice of ZnFe2O4. Jauhar et al. [20] carried out the degradation of cationic and anionic dyes with manganese substituted cobalt ferrites. The authors results revealed that the 90% of dye degradation was achieved in a time period of 40–90 min in dark and within 20–30 min under visible light irradiation. Liu et al. [21] evaluated the degradation of rhodamine B in the presence of oxalic acid using nickel ferrite as a catalyst and reported that the 1.0 mM oxalic acid was optimal condition for the degradation of dye at pH 3.0. The authors also showed that the catalyst have good degradation for rhodamine B even after seven cyclic.

From the literature, it has been observed that Mg2+ ions cause appreciable changes in the structural, magnetic and electrical properties of the ferrites and have gigantic importance in many fields. But the systematic study on the structural, magnetic, electrical properties of nanocrystalline Mg substituted Co–Zn ferrites along with their property to act as a photocatalyst has not yet been reported. So in the present work, synthesis magnesium substituted cobalt zinc ferrites in the nano range having formula Co0.6Zn0.4MgxFe2xO4 (x = 0.2, 0.4, 0.6, 0.8 and 1.0) via sol–gel auto combustion method was carried out. Structural, magnetic and electrical properties of prepared ferrites were also investigated in detail. The photo catalytic effect of Mg2+ substitution on the degradation of methyl orange was also performed.

Section snippets

Preparation of Co0.6Zn0.4MgxFe2−xO4 (x = 0.2, 0.4, 0.6, 0.8 and1.0) nanoferrites

Synthesis of ferrites having the formula Co0.6Zn0.4MgxFe2xO4, x = 0.2, 0.4, 0.6, 0.8 and 1.0 was carried out by the sol–gel auto-combustion method [22], [23], [24]. The AR Grade Fe(NO3)3.9H2O, Co(NO3)2.6H2O, Mg(NO3)2.6H2O, Zn(NO3)2.6H2O and citric acid were weighed in desired stoichiometric ratios and dissolved in minimum amount of distilled water. The individual solutions were then mixed together and the pH value of the solution was adjusted to about 6 by adding ammonia solution [25]. The mixed

EPMA analysis

Elemental analytical data for Co Fe, Mg and Zn in the samples were obtained by EPMA. About 2 mm thick pellets were prepared, fixed on the sample holder and coated with carbon to make them conductive. Analysis was carried out at eight different points of each pellet, which were very close. The elemental analytical data for Co, Mg, Zn and Fe in all the samples by EPMA matched well with the formula percentage of the ferrites. All the data of EPMA analysis is given in Table 1.

FT-IR characterization

According to Waldron

Conclusion

Magnesium doped cobalt ferrites having the chemical formula Co0.6Zn0.4MgxFe2xO4 (x = 0.2, 0.4, 0.6, 0.8 and 1.0) were successfully prepared by the sol–gel auto combustion method. XRD patterns revealed the formation of cubic spinel structure. Doping of magnesium enhanced the resistivity. Maximum resistivity was obtained for composition x = 0.8. Resistivity showed regular decrease with increase in temperature reflecting semiconductor behavior of the ferrite samples. The enhanced drift mobility of

Declaration

The article is original, has been written by the stated authors who are all aware of its content and approve its submission, has not been published previously, it is not under consideration for publication elsewhere, no conflict of interest exists, or if such conflict exists, the exact nature of the conflict must be declared and if accepted, the article will not be published elsewhere in the same form, in any language, without the written consent of the publisher.

Acknowledgements

The authors express their deep gratitude to DST (SERB, SR/S1/IC-28/2012) for providing grant under major research project and University Grants Commission (UGC) for providing Rajiv Gandhi fellowship to S. Bhukal.

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