Synergistic effect of co-existence of hematite (α-Fe2O3) and magnetite (Fe3O4) nanoparticles on graphene sheet for dye adsorption

•A novel rGO supported (α-Fe2O3 and Fe3O4) nanocomposite was synthesized.•RGO-Fe2O3-Fe3O4 showed better adsorption as compared to other rGO composites.•The maximum adsorption capacity was determined to be ∼75 mg/g.•The nanocomposite was stable for multiple adsorption cycles.

Graphene oxide (GO) functionalized with hematite (α-Fe2O3) and magnetite (Fe3O4) nanoparticles (rGO-Fe2O3-Fe3O4) was prepared using a facile one-step co-precipitation technique. It shows superior performance towards methylene blue (MB) adsorption for water purification, compared to GO functionalized with hematite (rGO-Fe2O3) or magnetite (rGO-Fe3O4) nanoparticles. It also shows better performance compared to a composite mixture of rGO-Fe2O3 and rGO-Fe3O4 (rGO-M). It has been postulated that the co-existence of hematite and magnetite nanoparticles on graphene sheet causes the synergistic effect towards MB adsorption. The adsorption behaviour of GO, reduced graphene oxide (rGO), rGO-Fe2O3, rGO-Fe3O4, rGO-Fe2O3-Fe3O4 and rGO-M was studied. These materials were characterized using XRD, XPS, Raman spectroscopy, TGA, TEM, VSM and BET surface area analyzer. The phases present in the as-synthesized adsorbents were identified by XRD, Raman and XPS techniques. TGA studies confirmed the strong bonding between iron oxide particles and graphene sheet. TEM characterization was used for nanoparticles morphology and size distribution studies. Kinetics of MB adsorption was well described by the pseudo second order model. Langmuir adsorption isotherm better fits the equilibrium adsorption behaviour of rGO-Fe2O3-Fe3O4 as compared to Freundlich isotherm and the maximum adsorption capacity was determined to be 72.8 ± 2.7 mg/g. Regeneration and reusability studies performed on rGO-Fe2O3-Fe3O4 revealed that it retains more than 65% of the original adsorption capacity even after 3 cycles thus making it a potential candidate for water treatment.

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