Synthesis, optical and photo-electrochemical properties of NiBi2O4 and its photocatalytic activity under solar light irradiation

Abstract

NiBi2O4 was synthesized by sol gel method using citric acid as a complexing reagent. The formed gel was dried and calcined for 9 h at three temperature steps (400, 600, 800 °C) to get a single phase with the spinel structure. The as-prepared NiBi2O4 was characterized by X-ray diffraction, FT-IR spectroscopy, and UV–vis diffuse reflectance. The optical band gap (Eg =1.76 eV) was obtained from optical absorption spectroscopy. The thermal variation electrical conductivity, measured in the range (300–473 K), is characteristic of semiconductor, with a conduction mechanism by low polaron hopping and activation energy of 0.2 eV. As application, the methylene blue (MB) was successfully oxidized upon solar light. A removal conversion of 40 % was obtained after 2 h at room temperature. The total photo-oxidation of MB (30 mg/L) was obtained on the new hetero-junction NiBi2O4/ZnO at natural pH in less than 2 h. A photocatalytic degradation mechanism occurred through (electron-hole) pairs generation and the redox reactions taking place on the NiBi2O4/ZnO surface of MB are proposed to explain the high activity under solar light irradiation. The degradation kinetics followed a first order with an apparent constant rate of 0.15 h-1.