Tailoring the photo-Fenton activity of spinel ferrites (MFe2O4) by incorporating different cations (M = Cu, Zn, Ni and Co) in the structure

Abstract

Magnetic bimetallic nanospinels (MFe₂O₄; M = Cu, Zn, Ni and Co) with sizes ranging between 15–30 nm were synthesized using a facile and viable sol–gel method. Fourier transform infrared spectral analysis of all the samples demonstrated the formation of M–O bond in the spinel structure. Structural exploration of all the nano materials using powder X-ray diffraction and high resolution transmission electron microscopy revealed the formation of a single phase cubic spinel structure. All the materials exhibited a magnetic temperament with high surface areas (92–151 m² g⁻¹). Furthermore, the band gaps calculated from the diffuse reflectance spectra were quite narrow (1.26–2.08 eV) for all the samples, hence the ferrites could act as visible light driven photocatalysts. The prepared nanospinels are proposed to be promising heterogeneous photo-Fenton catalysts under visible light for the degradation of organic pollutants. The catalytic results revealed that the rate of reaction was significantly influenced by the cation in the spinel structure as the degradation order was observed to be CuFe₂O₄ (k = 0.286 min⁻¹) > ZnFe₂O₄ (k = 0.267 min⁻¹) > NiFe₂O₄ (k = 0.138 min⁻¹) > CoFe₂O₄ (k = 0.078 min⁻¹). The reaction conditions were optimized for all the ferrites as the photodegradation was influenced by the ferrite dosage (0.25–1.00 g L⁻¹), pH (2–5) and the H₂O₂ concentration (4–27 mM). The experimental data disclosed that the ferrite activity was sensitive to sintering temperature. The materials displayed remarkable stability in the reaction as they could be magnetically separated using an external magnet and recycled for up to 4 consecutive cycles. There was no significant loss in activity of all the materials, demonstrating the excellent ability of the ferrites to remove organic pollutants from wastewater.