Fabrication of magnetically recoverable BiVO4/NiFe2O4 composites for the photocatalytic degradation of methylene blue

Abstract Bismuth vanadate (BiVO4) and nickel ferrite (NiFe2O4) nanoceramics were successfully synthesized using hydrothermal and sol-gel methods, respectively. Three different composites between magnetic NiFe2O4 and non-magnetic BiVO4 phases (25 wt% BiVO4 + 75 wt% NiFe2O4, 50 wt% BiVO4 + 50 wt% NiFe2O4 and 75 wt% BiVO4 + 25 wt% NiFe2O4) were prepared and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and UV–Visible spectroscopy. The PXRD analysis indicated the formation of well-defined composites between the two phases. All three composites were found to be magnetic in nature as confirmed from magnetic measurements carried out using vibrating sample magnetometer (VSM). The saturation magnetization (Ms) values found to be decreased almost linearly with increasing BiVO4 content in the composite, due to magnetic dilution induced in the composites by the non-magnetic BiVO4 phase. Band gaps of all the as-synthesized compounds were determined using diffuse reflectance spectroscopy (DRS) and are found to be in the visible region which makes them suitable for the photocatalytic dye degradation application. Among all the prepared magnetic composites, the composite with 50 wt% BiVO4 + 50 wt% NiFe2O4 exhibited the highest photocatalytic activity towards the degradation of 10 ppm methylene blue solution. Further enhancement of photocatalytic efficiency was achieved by the addition of a known volume of H2O2. Overall, 80% dye degradation efficiency was achieved using the composite of 50 wt% BiVO4 + 50 wt% NiFe2O4 under sunlight. Since the composites are magnetic in nature they can be easily separated from the heterogeneous reaction mixture using a laboratory magnet, after the photocatalytic treatment.