Preparation and characterization of the system NiMn₂O₄/TiO₂ by sol–gel: application to the photodegradation of benzamide under visible light

Benzamide is successfully degraded on the novel heterosystem NiMn₂O₄/TiO₂ under visible light. The nanosized spinel is synthesized by the sol–gel method at ~850 °C. The X-ray diffraction pattern shows narrow peaks and the oxides are well crystallized. The Mott–Schottky plot (C⁻²−E) of NiMn₂O₄ is characteristic of p-type conductivity from which a flat-band potential of −0.20 V_SCE is obtained. The energy-band diagram, built from the physicochemical characterizations, predicts the electron transfer from the conduction to dissolved oxygen via TiO₂. The loading of TiO₂ with NiMn₂O₄ enhances the photoactivity and NiMn₂O₄ islands achieve a colloidal photochemical heterosystem, tested successfully for the light-induced benzamide degradation. The spinel dose and benzamide concentration are optimized. Under the ideal conditions, the rate of the benzamide disappearance is controlled by high-performance liquid chromatography. A conversion of 85% is reported in aerated benzamide solution (15 ppm) in less than 2 h under artificial light. This conversion rate increases up to 94% under solar light and the oxidation obeys to a first-order kinetics with a half-life of 53 min.