Supraparamagnetic, Conductive, and Processable Multifunctional Graphene Nanosheets Coated with High-Density Fe3O4 Nanoparticles

The amazing properties of graphene are triggering extensive interests of both scientists and engineers, whereas how to fully utilize the unique attributes of graphene to construct novel graphene-based composites with tailor-made, integrated functions remains to be a challenge. Here, we report a facile approach to multifunctional iron oxide nanoparticle-attached graphene nanosheets (graphene@Fe3O4) which show the integrated properties of strong supraparamagnetism, electrical conductivity, highly chemical reactivity, good solubility, and excellent processability. The synthesis method is efficient, scalable, green, and controllable and has the feature of reduction of graphene oxide and formation of Fe3O4 nanoparticles in one step. When the feed ratios are adjusted, the average diameter of Fe3O4 nanoparticles (1.2−6.3 nm), the coverage density of Fe3O4 nanoparticles on graphene nanosheets (5.3−57.9%), and the saturated magnetization of graphene@Fe3O4 (0.5−44.1 emu/g) can be controlled readily. Because of the good solubility of the as-prepared graphene@Fe3O4, highly flexible and multifunctional films composed of polyurethane and a high content of graphene@Fe3O4 (up to 60 wt %) were fabricated by the solution-processing technique. The graphene@Fe3O4 hybrid sheets showed electrical conductivity of 0.7 S/m and can be aligned into a layered-stacking pattern in an external magnetic field. The versatile graphene@Fe3O4 nanosheets hold great promise in a wide range of fields, including magnetic resonance imaging, electromagnetic interference shielding, microwave absorbing, and so forth.