2.2. Synthesis of magnetic graphene
The graphene was synthesized with oil soluble food antioxidants as reducing agent (See supporting information). The magnetite (Fe3O4) magnetic nanoparticles were synthesized via a solvothermal process [28]. As shown in Fig. 1, the magnetic graphene was fabricated via a simple method by co-mixing according to our previous studies with some modifications [25], [28] and [38]. Briefly, Fe3O4 (2500 mg), PSA (1250 mg) and graphene (1000 mg) were placed in a 100 mL vial. After adding 30 mL acetonitrile, the magnetic graphene dispersive solution was obtained by vortexing vigorously for 1 min, and then an external magnet was attached to the outside bottom of the vial and the magnetic graphene was gathered to the bottom of the vial. The supernatant was discarded. The product was washed with toluene for several times. The washed product was then vacuum-dried at 60 °C overnight. The yield of magnetic graphene was approximately 100%, which was attributed to the complete retrieval of components during the mild co-mixing method.