Structural features, magnetic properties and photocatalytic activity of bismuth ferrite nanoparticles grafted on graphene nanosheets

Abstract

Graphene based visible light responsive photocatalysts have been actively used. Among various photocatalysts, bismuth ferrite (BiFeO₃), with a suitable band gap, has gained more attention. In this work, BiFeO₃ nanoparticles were prepared and grafted on graphene nanosheets (BiFeO₃-g-GNS). The morphology, photocatalytic, structural, optical and magnetic properties of BiFeO₃-g-GNS were investigated. The XRD analysis shows that the crystalline BiFeO₃ nanoparticles have a rhombohedral crystal structure with the R3c space group. Well decorated graphene nanosheets (GNSs) with spherical perovskite type BiFeO₃ nanoparticles (50–80 nm) are obtained, as confirmed by FESEM and HRTEM analysis. The Raman spectra and XPS spectra confirm the presence of different valence states (Fe³⁺, Bi³⁺) and chemical bonding (Fe–O, Bi–O) in BiFeO₃. The M–H curves (at 10, 297 and 380 K) do not show any hysteresis after grafting on the GNSs. Moreover, the magnetic domain structure and the magnetization behavior of the BiFeO₃ nanoparticles were discerned by MFM. The presence of GNSs reduces the band gap of BiFeO₃ to 2.07 eV (BiFeO₃-g-GNS) from 2.15 eV (pristine BiFeO₃). Improved photoluminescence (PL) characteristics and a higher BET surface area have also been observed in the case of BiFeO₃-g-GNS. The photocatalytic activities of pristine BiFeO₃ and BiFeO₃-g-GNS were tested by the degradation of cationic methylene blue (MB) and anionic methyl orange (MO) dyes. It has been observed that BiFeO₃-g-GNS exhibits a higher photocatalytic activity toward MB (87%) and MO (35.9%) than the pristine BiFeO₃ (57.9 and 4.1% respectively). Hence, the rate of photocatalytic degradation of the MB and MO dyes is significantly enhanced in the case of BiFeO₃-g-GNS compared to pristine BiFeO₃. The higher catalytic activity of BiFeO₃-g-GNS is attributed to its lower band gap, higher absorption in the visible region and reduced recombination of photogenerated electron/hole pairs in the presence of GNS. Herein, we demonstrate that the photocatalytic activity of the BiFeO₃ nanoparticles can be enhanced by grafting them on GNSs without influencing their magnetic and structural properties.