Photodegradation of methylene blue using magnetically reduced graphene oxide bismuth oxybromide composite

• Photocatalyst with relatively small band gap energy has been developed.
• The catalyst works well in the degradation of dye molecules in the visible region.
• Separation for recycle and reuse of the catalyst has been ensured by introducing magnetic properties to the catalyst.

A magnetically reduced graphene oxide–bismuth oxybromide (MRGO–BiOBr) composite was successfully synthesized and found to possess magnetic, adsorptive and photocatalytic properties. The synthesized composite have been characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray Diffraction (X-RD), Scanning electron microscopy (SEM) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). Presence of FeO bond stretching vibrations and bromo compounds have been confirmed using FT-IR and the diffraction peaks of the composite obtained from X-RD showed a combination of peaks of both MRGO and BiOBr. SEM images further confirmed the presence of minute flakes of BiOBr scattered onto the surface of MRGO. Reduction in band gap energy from 2.76 eV for pure BiOBr to 1.91 eV for the composite was determined using UV–vis DRS. Photocatalytic degradation of Methylene Blue dye under visible light irradiation (150 W Tungsten filament lamp) was examined using MRGO–BiOBr and around 96.84% of dye of 50 ppm was degraded in 2 h. Kinetic studies were done by splitting the kinetic data into 2 regions at 30 min of irradiation and using the Langmuir–Hinshelwood (L–H) model to determine the rate constants. The composite was found to be easily separable in the presence of a magnet and on regeneration, studies showed no significant decrease in the photocatalytic activity of the composite even after 3 runs.