Controlled synthesis, magnetic and photocatalytic properties of hollow spheres and colloidal nanocrystal clusters of manganese ferrite

Hollow spheres and colloidal nanocrystal clusters (CNCs) of MnFe2O4 with similar submicron scales have been synthesized controllably by a solvothermal method through simply adjusting the synthesis microenvironment. Morphology and microstructure of the products were investigated by the power X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Magnetic property measurements at room temperature showed that MnFe2O4 hollow spheres were ferromagnetic with a very small hysteresis loop while MnFe2O4 CNCs showed superparamagnetic behavior. Magnetization saturation values were about 76.5 and 63.4 emu/g for hollow spheres and CNCs, respectively. The band gaps for hollow spheres and CNCs were 1.68 and 1.74 eV, respectively, based on the results of diffuse reflectance spectra (DRS). MnFe2O4 hollow spheres showed higher photocatalytic activity under visible light to methylene blue than that of CNCs. Both of the samples also displayed an excellent recycle performance. Formation mechanisms of MnFe2O4 hollow spheres and CNCs, and the relationship between their structure and properties, have been studied based on the experimental results.