Controlled Preparation Of Fe₃O₄-based Nanocomposites And Their Microwave Absorption Properties Research

In this paper,we modified the traditional electromagnetic wave absorbing material of Fe3O4 based on the component and structure design,and by varying the experimental conditions,prepared a kind of Fe3O4-based nanocomposites with light weight,strong absorption and wide absorption bandwidth.The main contents and results of this research are as follows:Firstly,monodisperse Fe3O4 nanoparticles and well-defined Fe3O4/RGO(Reduced Graphene Oxide)nanocomposites were prepared by a solvothermal method.Moreover,the size of Fe3O4 nanoparticles can be controlled by adjusting the concentration of FeCl3·6H20 in ethylene glycol/diethylene glycol(EG/DEG)binary solvent mixtures.Analysis and detection results show that:The electromagnetic wave absorption properties of the as-synthesized samples are seriously affected by the size of Fe3O4 nanoparticles,and the Fe3O4/RGO nanocomposites exhibit better electromagnetic wave absorption capabilities in comparison with pristine Fe3O4 nanoparticles.The effective bandwidth of Fe3O4/RGO nanocomposites is up to 14.5 GHz(2.8?15.4 GHz and 15.4?18.0 GHz)in the thickness of 1.0?5.5 mm.The minimum reflection loss can reach about-28.9 dB at 10.7 GHz with a thickness of 2.5 mm.The outstanding electromagnetic wave absorption properties can be attributed to the cooperation effect between dielectric loss and magnetic loss,enhanced interfacial polarization,high surface area and layered structure of RGO.Secondly,core-shell structured Fe3O4@ZnO and Fe3O4@SnO2 nanoparticles were prepared and their electromagnetic wave absorption properties were also investigated.Analysis and detection results show that:Due to the thin ZnO shell,the electromagnetic wave absorption properties of Fe3O4@ZnO nanoparticles are not as ideal as expect whether the filling ratio is 30 wt-%or 70 wt-%.Whereas,Fe3O4@SnO2 microspheres(filling ratio:50 wt-%)exhibit extraordinary electromagnetic wave absorption properties at the low frequency range whether the average particle size of Fe3O4 is 120 nm or 220 nm.The remarkable electromagnetic wave absorption properties are closely related with the appropriate match between the complex permittivity and permeability,enhanced interfacial polarization and the unique core-shell structure.Thirdly,core-shell structured Fe3O4@SiO2 and Fe3O4@ZnO@SiO2 nanoparticles were prepared and their electromagnetic wave absorption properties were also investigated.Furthermore,the SiO2 shell thickness can be tailored by adjusting the tetraethyl orthosilicate and ammonia contents in the mixed solvent.Analysis and detection results show that:The SiO2 shell thickness has a significant effect on the electromagnetic wave absorption properties.Compared with the original Fe3O4 nanoparticles,Fe3O4@SiO2 nanoparticles with thin SiO2 shells present enhanced electromagnetic wave absorption properties(Frequency range:2.0?18.0 GHz,Absorber thickness:1.5?5.5 mm).And the Fe3O4@ZnO@SiO2 nanoparticles show stronger electromagnetic wave absorption properties than that of Fe3O4@SiO2 nanoparticles,which may result from the introduction of dielectric ZnO and dual core-shell structure.Fourthly,Fe3O4@ZnO/RGO nanocomposites were prepared by combining the solvothermal method with a sol-gel process.In addition,the electromagnetic wave absorption properties were studied in the frequency range of 2.0?18.0 GHz with the absorber thickness of 1.0?5.5 mm.Analysis and detection results show that:The bandwidth corresponding to the reflection loss below-10.0 dB is 11.2 GHz(3.7?11.0 GHz,11.8?12.9 GHz and 15.2?18.0 GHz)and the minimum reflection loss value can reach-31.1 dB at 6.7 GHz with a thickness of 4.5 mm.The electromagnetic data demonstrate that Fe3O4@ZnO/RGO nanocomposites exhibit enhanced electromagnetic wave absorption properties compared with Fe3O4/RGO nanocomposites,which probably originate from the unique core-shell structure,multiple interfacial polarization and dielectric loss type material of ZnO.Fifthly,Fe3O4@SnO2/RGO nanocomposites were prepared by a facile solvothermal method and the SnO2 contents can be tuned by adjusting the amount of SnCl4·5H2O and NaOH.Analysis and detection results show that:The introduction of SnO2 in Fe3O4/RGO nanocomposites can significantly enhance the electromagnetic wave absorption properties.The absorption bandwidth with reflection loss below-10.0 dB is up to 14.4 GHz(from 3.6 to 18 GHz)and the reflection loss values exceeding-20.0 dB(99%absorption)are reached in the frequency range of 5.2?7.5 GHz(Frequency range:2.0?18.0 GHz,Absorber thickness:1.0?5.5 mm).The minimum reflection loss can reach about-45.5 dB at 6.4 GHz with a thickness of 4.5 mm.The excellent electromagnetic wave absorption properties of Fe3O4@SnO2/RGO nanocomposites are related to the unique core-shell structure,good impedance match and multiple loss mechanism.Lastly,Fe3O4@SiO2/RGO nanocomposites(the thickness of SiO2 shells are around 20 nm)were prepared by solvothermal method and sol-gel process.Moreover,the electromagnetic wave absorption properties were investigated in the frequency range of 2.0?18.0 GHz with the absorber thickness of 1.0?5.5 mm.Analysis and detection results show that:The Fe3O4@SiO2/RGO nanocomposites exhibit significantly improved electromagnetic wave absorption properties when compared with the original Fe3O4/RGO nanocomposites,which is due to the unique core-shell structure,multiple loss mechanism and wave transparent material of SiO2.Furthermore,the introduction of SiO2 can protect Fe3O4 nanoparticles from oxidation,corrosion and enhanced the high temperature stability.In conclusion,as-prepared Fe3O4-based nanocomposites can not only effectively improve the high density and poor stability at high temperature of Fe3O4 nanoparticles as absorbing materials,but also promote the composites in composition,structure and magnetic properties that cooperate with each other,realizing effective absorption of electromagnetic wave.The work in this paper is expected to provide technological support and theoretical basis for the preparation of Fe3O4-based electromagnetic wave absorption materials with structural and functional properties combined.