Physical and photo-electrochemical properties of MgFe₂O₄ prepared by sol gel route: application to the photodegradation of methylene blue

The spinel MgFe₂O₄ synthesized by sol gel method, was characterized by physical and electrochemical methods. The thermal analysis (TG) gives an optimal synthesis temperature of 650 °C where the X-ray diffraction pattern exhibits a single phase crystallizing in a cubic symmetry (Space Group: Fd$\stackrel{-}{3}$m) with spherical crystallites (~ 0.45 µm). The morphology observed through the SEM image shows elliptical and spherical grains of ~ 0.8 µm. The spinel possesses a direct optical transition (2.16 eV) due to electrons transfer Fe³⁺: d−d transition, coming from the crystal field splitting in agreement with the red color. The low electrons mobility is assigned to a narrow conduction band of Fe³⁺: 3d parentage with activation energy (0.14 eV) in conformity with a conduction mechanism by small polaron hopping. The semi-logarithmic plot confirms the chemical stability of oxide. Unlike other spinels, the capacitance plot exhibits n type conduction confirmed by chrono-amperometry with a flat band potential (E_fb) of 0.27 V. The electrochemical impedance spectroscopy displays a semi-circle attributed to the bulk behavior. As application, the photodegradation of methylene blue (10 mg L^− 1) was successfully on the spinel suspension; 87% are eliminated after 2 h of exposure to sunlight irradiation.