Magnetic NiFe2O4 3D nanosphere photocatalyst: Glycerol-assisted microwave solvothermal synthesis and photocatalytic activity under microwave electrodeless discharge lamp

Abstract In this study, NiFe2O4 (NFO) nanocrystalline powder was synthesized using a glycerol-assisted microwave solvothermal process followed by annealing. In comparison with the traditional preparation method, this method does not require addition of any precipitate-controlling agents. The structural properties of NFO were characterized via different techniques, such as X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and ultraviolet–visible diffuse reflection spectra. The results suggested that the NFO crystal was a three-dimensional (3D) porous nanosphere with a diameter of approximately 400 nm, and the glycerol added during the preparation process played a crucial role in the formation of 3D nanospheres. The photocatalytic activity of NFO was evaluated by the degradation of methylene blue (MB) in a microwave electrodeless discharge lamp (MEDL) system. Additionally, the mechanism of MB photocatalytic degradation was studied. The results suggest that 88.6% of the MB degraded within 10 min under MEDL irradiation, and the mineralization rate reached 55%. The main active species of MB degradation were e-, h+, and •O2−. In addition, the cycle catalysis experiment confirmed the reusability of NFO 3D nanospheres. We believe that the NFO 3D nanospheres can serve as efficient photocatalysts suitable for MEDL systems.