Investigation of structural, magnetic and photocatalytic properties of Gd doped bismuth ferrite-reduced graphene oxide nanocomposites

Abstract

The synthesis as well as structural, magnetic, optical and photocatalytic properties of sillenite and perovskite type undoped and Gd-doped bismuth ferrite-reduced graphene oxide (BiFeO3-rGO) nanocomposites have been investigated. Graphite oxide was initially prepared using modified Hummer’s method, followed by hydrothermal synthesis of the nanocomposites at different reaction temperatures. The X-ray diffraction measurements confirmed the formation of perovskite type BiFeO3-rGO composites at a reaction temperature of 2000C which is the lowest temperature for the formation of this phase, However, a structural transition to sillenite type (Bi25FeO40) was observed at 1800C. Such phenomenon is notable since simply by tweaking the temperature by 200C, composite of desired phase of bismuth ferrite with rGO may be formed keeping all other conditions same. The FESEM images demonstrated that the particle size of the perovskite nanocomposites was ∼25-60 nm, and for the sillenite phase composites it was ∼10-30 nm. With Gd doping, similar phases were obtained, however, impurity phases were present and the particles were of larger size. The assynthesized composites exhibited significantly enhanced saturation magnetization over pure BiFeO3 nanoparticles, with Bi25FeO40-rGO composite having higher saturation magnetization than all other samples. Among the Gd-doped composites, the perovskite phase provided higher magnetization compared to the sillenite one which might be attributed to the impurities involved. The optical characteristics of the nanocomposites demonstrated considerably higher absorbance in the visible range with significantly lower band gap in comparison to pure BiFeO3. Again, sillenite type Bi25FeO40-rGO composite was found to have lower bandgap compared to the perovskite counterpart. In this case, higher bandgaps were obtained for the Gd-doped composites in comparison with the undoped composites which may be due to larger particle size of the doped samples. Next, the photocatalytic and H2 production experiments were investigated. The photocatalytic efficiency of a material depends on its bandgap, surface morphology and particle size distribution. Keeping this in mind, undoped perovskite and sillenite composites were chosen for experimentation as these provided the most promising relevant properties. The composites provided higher photocatalytic efficiency and stability than pure bismuth ferrite and between the composites, sillenite Bi25FeO40-rGO once again provided enhanced performance. This composition demonstrated higher H2 production results among all the samples, notably providing 3.5 times enhancement over commercially available TiO2. The present investigation provides a means of selective transition as desired between composites of rGO with perovskite and sillenite phase bismuth ferrite by temperature control and the results suggest that incorporation of graphene with sillenite type bismuth ferrite provides enhanced performance in terms of all the properties investigated. Moreover, composites of rGO with 10% Gd-doped bismuth ferrites did not provide enhancements in the properties and further investigations are necessary to improve the properties of the rare earth doped bismuth-rGO nanocomposites.