Photocatalytic degradation of bromothymol blue over MgFe2O4 under sunlight exposure

Abstract

The spinel MgFe2O4 was synthesized by the sol-gel procedure, which exhibits a distinct single-phase X-ray diffraction pattern. Thermal analysis (TG) revealed that crystallization occurs above 700 °C yielding a cubic symmetry (Space Group: Fd−3 m). Scanning electron microscopy revealed nano-spherical structures with an average length of ∼0.6 μm. A direct transition of 2.16 eV determined from the diffuse reflectance is associated with the internal electron transfer Fe3+: d−d, in conformity with the red colour of the oxide. The activation energy (Ea = 0.14 eV), derived through the thermal variation of the conductivity, caused by the low polaron hopping among mixed valences Fe3+/2+ with weak electron mobility (μe = 2 × 10−6 m2V−1s−1). The capacitance versus polarization potential indicated n-type semi-conductivity, supported by chrono-amperometry, with a flat band potential (Efb) of 0.27 VSCE. The effectiveness of MgFe2O4 as a photocatalyst for the oxidation of Bromothymol Blue (BB) under solar light was assessed, while the outcomes showed a 65% decrease at pH 3 within 180 min. The BB oxidation follows a first-order kinetic model with a rate constant K app of 0.0053 min−1 (t1/2 = 110 min). A BB degradation mechanism was proposed per the results gathered through Mott-Schottky and UV–vis analyses. In summary, this current study has demonstrated that MgFe2O4 has promising potential as an alternative photocatalyst for environmental cleansing.