Physical and photo-electrochemical characterization of Ca2Fe2O5 for metronidazole antibiotic degradation under sunlight

Abstract

This study aims to investigate and describe the properties of the brownmillerite Ca2Fe2O5, synthesized from nitrates precursors. The X-ray diffraction showed that the single phase crystallizes in an orthorhombic symmetry (Space Group: Pcmn) with a specific surface area of 8.16 m2 g−1. The d-d transition of Fe3+: in octahedral coordination gives a direct optical band gap (2.02 eV) as determined by diffuse reflectance spectroscopy in agreement with the brown color of the oxide. The first one is due to the charge transfer O2−: 2p → Fe3+: t2g. This enables the material to exploit a large part of the solar radiation for photocatalytic purposes. The chemical stability of Ca2Fe2O5 is demonstrated over the pH range (5–12). The capacitance-potential plot revealed n-type conduction; a flat band potential of (Efb) 0.40 VSCE and electron concentration (NA) of 8.57 × 1024 m−3 were obtained in Na2SO4 (0.1 M) solution. The intensity-potential (J - E) profile showed electrochemical stability with oxygen intercalation in the layered lattice. The conduction band is more anodic than the level of O2/O2•, allowing the successful oxidation of Metronidazole by •O2− radical under visible light. The photodegradation of Metronidazole (MNZ) was successfully achieved at an initial concentration of 10 mg/L under solar radiation and a photocatalyst dose of 1 g/L at a free pH after 120 min of exposure and obeys a first-order kinetic with a rate constant of (33.7 × 10−3 min−1).