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

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 H2O2 as 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.