MnFe2O4 nanoparticulate obtained by microwave-assisted combustion: An efficient magnetic catalyst for degradation of malachite green cationic dye in aqueous medium

Abstract

The reaction of Mn(NO3)2, Fe(NO3)3 and citric acid assisted by microwave allowed the preparation of nanoparticles of MnFe2O4. The diffraction patterns were assigned to the cubic phase and the material crystallize in the space group Fd-3m (Oh7, n° 227). A full analysis of the infrared bands through group theory showed that four bands, F1u, are active in the IR and five A1g, Eg and 3F2g, are detected in the Raman spectrum. Neither of them is coincident. The HRTEM confirmed the nanometric size of MnFe2O4 and allowed the determination of the inter-planar distances, 0.164, 0.256, and 0.300 nm, in the polycrystalline sample. The SEM images show the formation of irregular-shaped agglomerates. A ζ of (−21.4 ± 0.3) mV was obtained for the aqueous suspension of MnFe2O4. The catalytic degradation of the malachite green (MG) was studied using a mixture of H2O2 and MnFe2O4 nanoparticles. The dye was completely decomposed after 60 min forming colourless products. In addition, the kinetic study revealed that the degradation process follows a first-order Langmuir-Hinshelwood kinetics. Finally, we have investigated the toxicity of the degraded products in comparison with the original material, in the presence of brine shrimp (A. Salina). The results showed that a non-degraded solution of malachite green is 70% more lethal for this microorganism than the products obtained after the degradation process.