Synthesis of nanostructured graphene/Fe3O4(GF) hybrid:

The synthesis of GF was carried out by the in situ generation of Fe3O4 nanoparticles in a graphene oxide suspension by chemical co-precipitation of Fe2+ and Fe3+ ions followed by hydrazine reduction. Prior to GF synthesis, an aqueous suspension of graphene oxide (GO) was synthesized from natural graphite powders using a modied Hummers method.In a typical process, 7 g of graphite was charged into a 1 L beaker and was heated for 10 s in a microwave oven; this expanded the graphite to 150–200 times its original volume. The resulting graphite was dispersed in concentrated H2SO4 (1000 mL) at 0 C with continuous stirring. Then, 42 g of KMnO4 was slowly added so that the temperature did not exceed 20 C. The temperature was then elevated to 35 C, and the suspension was stirred for 2 h. The flask was then chilled again in the ice bath, and distilled water (ice) was slowly added, maintaining the temperature below 70 C. The mixture was stirred for 1 h and subsequently diluted with 5 L of deionized water. Subsequently, 50 mL of H2O2 (30 wt%) was added, and vigorous bubbles appeared as the color of the suspension changed from dark brown to yellow. The suspension was centrifuged and washed with 10% HCl solution four times, followed by centrifuging at 10 000 rpm and washing with deionized water to completely remove the acid until the pH of the GO dispersion reached 6. At this point, the as-synthesized GO dispersion was a paste. The concentration of GO was 1.0 wt%, as determined after drying the GO dispersion at 80 C under vacuum for 24 h. Next, 100 mL of the GO suspension was diluted to 200 mL and was ultrasonicated for 30 min. A solution of 1.0MFeCl2$4H2O and 2.0MFeCl3 was slowly added to the GO solution and was precipitated with a 1 M NH4OH solution slowly with continuous stirring, maintaining the pH at 10. After 3 h of stirring, 10 mL of hydrazine was added to the reaction solution, and the temperature was raised to 80 C with further stirring for 5 h. The resulting solution was cooled to room temperature, filtered out and washed thoroughly with distilled water. The Fe3O4 decorated grapheme nanoparticles (GF) thus obtained were dried at 80 C in a vacuum oven. Pristine Fe3O4 nanoparticles were also formed in a similar manner without the addition of GO. The formation of Fe3O4 nanoparticles in graphene was confirmed by X-ray diffraction (XRD).

In a second experiment, we introduced ferrofluid in RGO matrix which is as follows:

For the synthesis of graphene oxide modified Hummers method was used. In brief commercially available graphite powder (5 g) and NaNO3 (5 g) is mixed into concentrated H2SO4 (230 ml). KMnO4 (40 g) is added gradually with stirring and cooling, so that the temperature of the mixture is not allowed to reach beyond 20 °C.The mixture is then stirred at 35 °C for 2 h, and deionized water (200 ml) is added. The reaction is stirred for 1 hour by the addition of a large amount of deionized water (300 ml) and 30% H2O2 solution (30 ml), causing violent effervescence and an increase in temperature to 100°C, after which the color of the suspension changes to bright yellow. The suspension is washed with 1:10 HCl solution (100 ml) in order to remove metal ions. The paste collected is dried at 60 °C. The resultant powder is dispersed in distilled water followed by stirring and ultrasonication for 3 hours. RGO is thereafter produced by reducing graphene oxide with hydrazine hydrate.

100 ml double distilled water in a 1 L beaker was taken. 1 M FeCl3 in the distilled water was mixed and ultrasonicated for 30 min. 1 wt%, 5wt%, 10 wt% and 15 wt% reduced graphene oxide were mixed in above sonicated solution of FeCl3 in order to achieve different conducting ferrofluid composites, and named as CFF01, CFF05, CFF10 and CFF15 respectively. The mixture was again ultrasonicated for another 1 h in order to homogenize the whole solution. Finally, it was magnetically stirred. During vigorous stirring 1M ammonia solution was mixed in 20 min till the pH value of solution reaches 9-10. After 2 h, an external magnet below the beaker was put in order to separate out water and Fe3O4 nanoparticles sandwiched in graphene layers. To obtain ammonium and chloride free particles, the precipitate was washed twice with distilled water, as a solvent, in order to prevent the presence of impurities in the final product. To isolate the supernatant liquid, the beaker contents were then centrifuged for 15 min at 4000 rpm. The supernatant liquid was then decanted, and centrifuged until only thick black precipitate remained. Conducting ferrofluid remained suspended in the liquid medium (with the addition of surfactant 25% TMAH in water). The solution thus obtained exhibited spikes when placed in the proximity of a strong magnet and was used for further study.