Microwave-assisted rapid synthesis of Co۳O۴ nanorods from CoC۲O۴.۲H۲O nanorods and its application in photocatalytic degradation of methylene blue under visible light irradiation

In this work, Co۳O۴ nanorods were successfully prepared by microwave-assisted solid state decomposition of rod-like CoC۲O۴.۲H۲O precursor within a very short reaction time (۶ min) without the use of a solvent/surfactant and complicated equipment. The as-obtained Co۳O۴ 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 Co۳O۴ nanorods have a length of ۱-۳ µm and diameter of ۴۰-۸۰ nm. FT-IR, XRD, EDX and selected-area electron diffraction demonstrated that the nanorods are composed of pure cubic phase Co۳O۴. Magnetic measurements at room temperature suggested the existence of a weak ferromagnetic behavior. The optical spectrum indicated two direct band gaps at ۲.۲۰ and ۳.۶۰ eV with a blue shift compared with the bulk sample. The photocatalytic activity of Co۳O۴ nanorods was investigated for the degradation of methylene blue (MB) as a model of dye pollutants in the presence of H۲O۲ as a green oxidant. The Co۳O۴ nanorods showed high efficiency for the degradation of MB dye by using H۲O۲ 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.

Keywords:

Co۳O۴ nanorods , Methylene blue dye , Microwave irradiation , Photocatalytic degradation , Transition metal oxides