Manganese substituted cobalt ferrites as efficient catalysts for H2O2 assisted degradation of cationic and anionic dyes: Their synthesis and characterization

• CoMnxFe2−xO4 (0.2 < x < 1.0) synthesized using sol–gel auto-combustion method.
• Mn3+ ions occupy octahedral sites of the ferrite sub-lattice.
• Structural, magnetic and electrical properties correlated with cation distribution.
• Ferrites employed for catalysis of decomposition of hydrogen peroxide solution.
• Catalytic activity of ferrites increases with increase in Mn3+ concentration.

Manganese substituted cobalt ferrites of the formula CoMnxFe2−xO4 (x = 0.2, 0.4, 0.6, 0.8 and 1.0), were synthesized by means of sol–gel auto combustion method and were annealed at different temperatures. The annealed ferrite compositions were characterized using FT-IR spectroscopy, Transmission Electron Microscopy (TEM) and powder X-Ray Diffraction techniques, substantiating the formation of pure phase ferrites. The saturation magnetization values of the entire ferrite compositions displayed a decreasing trend with increasing concentration of manganese ion, implying substitution of iron ions by manganese ions in the octahedral sites of the ferrite lattice. Additionally, the catalytic properties of these ferrites were studied. For this purpose, the ferrites were employed as heterogeneous catalysts in H2O2 assisted degradation of cationic and anionic dyes. The dyes chosen were Methylene Blue (cationic dye) and Remazol Turquoise Blue (anionic dye). The catalytic degradation of both the dyes was performed in dark as well as under visible light irradiation. Over 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. In all the reactions, it was observed that the presence of Mn3+ ions in the cobalt ferrite lattice significantly augmented the degradation of dyes. Further, an increase in dye degradation was observed with increase in manganese content. The increase in the catalytic efficiency of the ferrites was correlated with their cation distribution, deduced from the saturation magnetization values on the basis of Neel's two sub-lattice model.

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