Investigation Of Magneto-thermal And Microwave Absorption Properties Of Organic/Inorganic Nanocomposites Based On Fe₃O₄

In recent years,with the advancement of various nano synthesis technologies,magnetic nanoparticles have a wide range of applications in biomedical systems and in modern high-technology fields.Magnetic heating of nanoparticles has received increased attention as a unique platform to trigger specific biological reactions in various biomedical systems.In addition,electromagnetic radiation and pollution has become a serious problem with the development of 5G technology as it threatens human health and the normal operation of electronic devices.Magnetic Fe₃O₄particles,as a typical ferrite,have been widely studied as microwave absorbing materials due to their high saturation magnetization strength,high permeability,unique magnetic properties,and semi-metallic properties.Different morphological preparation methods and compounding with different organic/inorganic materials can affect the final properties of Fe₃O₄nanoparticles,based on which the following studies have been done.First,Fe₃O₄ nanorods were prepared using hydrothermal and ligand-assisted reduction methods,and controlled multidrug release was achieved by constructing a unique composite hydrogel structure consisting of two layers of agar hydrogel with magnetically aligned anisotropic Fe₃O₄nanorods in each layer.Due to the orthogonal arrangement of Fe₃O₄nanorod chains in the two layers,the controlled multidrug release can be triggered by the magnetocaloric anisotropy in different layers of the composite hydrogel,which depends on the direction of the external alternating magnetic field.By switching the magnetic field direction from 0°to 90°,the thermally triggered release of methylene blue（MB）is increased up to 1.4 folds.The physical source of magnetocaloric anisotropy is magnetic anisotropy.When switching the magnetic field direction from 0°to 90°,the composite hydrogel as designed showed a significant opposite drug release trend.This opposite drug release trend was significantly maintained after switching the magnetic field direction more than four times.This work opens a promising avenue for achieving the combination of magnetothermal therapy and remotely controllable multidrug combination therapy.Second,core-shell structured Fe₃O₄@Si O₂nanomaterials with different morphologies were prepared to obtain an electromagnetic wave absorption material with strong absorption capacity and light weight.The precursor Fe OOH@Si O₂nanorods were reduced to hollow and porous core-shell structured Fe₃O₄@Si O₂nanorods by gas-phase reduction and oil-phase reduction,respectively.The core-shell structured Fe₃O₄@Si O₂nanorods were prepared by the Oswald ripening mechanism and a modified St?ber method.The microwave absorption properties of Fe₃O₄@Si O₂composites with different morphologies were investigated.Among the magnetic Fe₃O₄@Si O₂composites,the core Fe₃O₄is completely wrapped by Si O₂.Here,the electromagnetic parameters of the composites were effectively tuned by the combination of magnetic Fe₃O₄and dielectric Si O₂.The results show that the prepared Fe₃O₄@Si O₂porous nanorod sample exhibit good absorption performance with a minimum reflection loss（RL）of-59.49 d B at 3.18 mm and an effective absorption bandwidth（RL<-10 d B）of 4.51 GHz at 3.52 mm（4.73～9.24 GHz）.It is believed that the good absorption performance arises from the synergistic effect of interfacial polarization in dielectric loss and natural resonance in magnetic loss.This work provides a versatile strategy for Fe₃O₄@Si O₂composites with a unique core-shell structure and excellent tunable microwave absorption properties.