Microwave-assisted rapid synthesis of Co3O4 nanorods from CoC2O4.2H2O nanorods and its application in photocatalytic degradation of methylene blue under visible light irradiation

Abstract

In this work, Co₃O₄ nanorods were successfully prepared by microwave-assisted solid state decomposition of rod-like CoC₂O₄.2H₂O precursor within a very short reaction time (6 min) without the use of a solvent/surfactant and complicated equipment. The as-obtained Co₃O₄ nanorods were fully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–Vis), energy-dispersive X-ray spectroscopy (EDX), and magnetic measurements. TEM and SEM images showed that the Co₃O₄ nanorods have a length of 1-3 µm and diameter of 40-80 nm. FT-IR, XRD, EDX and selected-area electron diffraction demonstrated that the nanorods are composed of pure cubic phase Co₃O₄. Magnetic measurements at room temperature suggested the existence of a weak ferromagnetic behavior. The optical spectrum indicated two direct band gaps at 2.20 and 3.60 eV with a blue shift compared with the bulk sample. The photocatalytic activity of Co₃O₄ nanorods was investigated for the degradation of methylene blue (MB) as a model of dye pollutants in the presence of H₂O₂as a green oxidant. The Co₃O₄ nanorods showed high efficiency for the degradation of MB dye by using H₂O₂ under visible light irradiation. Trapping experiments indicated that hydroxyl (^•OH) radicals were the main reactive species for dye degradation in the present photocatalytic system. In addition, the possible photodegradation mechanism was also proposed based on the trapping experiment results.