| The controllable preparation and electromagnetic (EM) wave absorption application of graphene (GN)-based magnetic composites were systematically studied in this paper. The research contained the preparation and surface modification of graphene, the controllable preparation of porous Fe3C>4 nanoparticles, the preparation and the optimum design of the EM wave absorption properties of the composites such as GN-Fe3O4 and GN-Fe3O4@ZnO. This work laid a good foundation for the research of multicomponent composites for EM wave absorption. The details were described as below:(1) The graphene was prepared by the reduction of graphite oxide in the presence of sodium dodecylbenzenesulfonate (SDBS). Most of oxygen functional groups were removed and only several stable functional groups were left after the reduction. The surface of graphene modified by SDBS was absorbed by many sulfonic acid groups ( -SO3-), which would provide active sites for the decorating of Fe3O4 nanoparticles.(2) The Fe3O4 nanoparticles were prepared by mixed-solvent method. It was found that both of the morphology and size of the nanoparticles greatly depend on the volume ratio of ethylene glycol (EG) and propylene glycol (PG). The monodispersed flower-like porous Fe3O4 nanoparticles with high saturation magnetization were obtained when VEG=VPG. The EM parameters of paraffin wax containing 70 wt-% porous Fe3O4 were measured, the values of real permittivity (ε’) and imaginary permittivity (ε") were both larger than solid Fe3O4, and an obvious dielectric resonance peak was observed. The reflection loss (RL) reaches its minimal value of-32 dB at 5.6 GHz and 11.2 GHz respectively.(3) The porous Fe3O4-decorated graphene (GN-Fe3O4) magnetic composites were successfully prepared by in-situ synthesis and two-step methods. Both of them were controllable by changing the experimental conditions:the GN-Fe3O4 magnetic composites of different Fe3O4 loading contents obtained by controlling the dosage of iron source FeCl3·6H2O and NaAc in the in-situ synthesis; the GN-Fe3O4 magnetic composites of different sizes and morphologies obtained by controlling the VEG/VPG of the mixed-solvent in the two-step synthesis.(4) The prepared GN-Fe3O4 composites showed good magnetic response properties and could be easily collected by a permanent magnet, indicating the strong interaction between the GN sheets and Fe3O4 nanoparticles. All of the GN-Fe3O4 composites exhibited better EM wave absorption properties than pure Fe3O4. The EM parameters of the GN-Fe3O4 magnetic composite were adjusted by controlling the loading content, size and morphology of Fe3O4, optimizing the EM wave absorption properties. The porous GN-Fe3O4 obtained when FeCl3·6H2O=0.255 g and VEG=VPG showed the optimum EM wave absorption properties. The minimal RL of paraffin wax containing 30 wt-% porous flower-like GN-Fe3O4 was almost-35 dB at 16.4 GHz and 5.0 GHz with the absorbing thickness of 1.0 mm and 4.0 mm, respectively. Besides, the absorption bandwidth corresponding to RL<-10 dB (over 90% EM wave absorption) was almost up to 12.6 GHz (4.2 GHz～13.0 GHz,14.2 GHz～18.0 GHz).(5) The core/shell Fe3O4 at ZnO-decrated graphene (GN-Fe3O4@ZnO) ternary composites were prepared by two-step method. The porous Fe3O4 cores were approximately 200 nm, and the thickness of ZnO layer was approximately 15 nm which was composed of many small ZnO nanocrystals. The GN-Fe3O4@ZnO ternary composites exhibit unique EM wave absorption properties with the thicknesses in the range of 1.0 mm-4.0 mm. Two RL peaks of paraffin wax containing 30 wt-% GN-Fe3O4@ZnO were observed, one strong peak at high-frequency and one comparatively weak peak at low-frequency. Besides, the absorption bandwidth corresponding to RL<-10 dB was almost up to 11.4 GHz (3.0 GHz-6.8 GHz,10.4 GHz～18.0 GHz), and the minimal RL is almost -40 dB. The results demonstrate that GN-Fe3O4@ZnO composites are very promising for the applications in lightweight, strong absorption, as well as broad frequency bandwidth EM absorber. |
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