Tuning Of Structure And Properties Of Spinel Magnesium Ferrite,Manganese Ferrite And Its Composites

Magnetic nanomaterials have unique physical and chemical properties and are used more and more widely in many fields of modern science such as magnetic storage,catalysis,magnetic fluids,targeted drug delivery,and magnetic hyperthermia.Among them,AB₂O₄ type spinel ferrite nanomaterials have attracted much attention because of their excellent electrical,magnetic properties and huge application potential.Due to the particle size,particle morphology,chemical composition and other factors of nanomaterials,the physical properties,chemical properties and applications of ferrite nanomaterials have an important impact.Therefore,it is of great theoretical and practical significance to regulate and synthesize the particle size,morphology and chemical composition of ferrite nanomaterials,and to study the relationship between microstructure and properties.As a coating material silica?SiO₂?has many special advantages:prevention of interaction between magnetic particles,good stability,good biocompatibility,etc.,in addition to the silica shell layer also has good hydrophilicity and acid resistance.Therefore,the synthesis and application of AB₂O₄@SiO₂ magnetic nanocomposites with core-shell structure have also received extensive attention from researchers.In this paper,the regulation and synthesis of two typical spinel ferrite nanomaterials,magnesium ferrite and manganese ferrite are studied by solvothermal method and chemical coprecipitation method.We studied the effects of their particle size,morphology and chemical composition on the magnetic properties,and analyzed the influence of the surface coated silica on the magnetic properties of ferrite nanomaterials.The main experimental contents are as follows:?1?We synthesized magnesium ferrite spinel magnetic nanoparticles with good dispersibility by solvothermal method.We find that the reaction time and temperature have a significant effect on the grain size and magnetic properties of the synthesized magnesium ferrite nanoparticles,so we design a synthetic route for different reaction conditions.The results of X-ray diffraction?XRD?analysis show that the magnesium ferrite magnetic nanoparticles synthesized at 180 ^oC for 12 h have typical spinel structure and high magnesium ferrite content and good crystallinity.The transmission electron microscopy?TEM?images were observed by transmission electron microscopy show that the size of most synthesized magnetic nanoparticles are in the range of 100¹50 nm.The EDS spectra of magnesium ferrite magnetic nanoparticles were observed by scanning electron microscopy.The main elements of the synthesized magnesium ferrite powders are Mg,Fe and O,and no other impurity elements are found.The magnetic properties of magnesium ferrite magnetic nanoparticles were measured by a vibrating sample magnetometer?VSM?.The maximum saturation magnetization of spinel magnesium ferrite magnetic nanoparticles is 67.35 emu/g at 180 ^oC for 12 h.?2?MnFe₂O₄ magnetic nanoparticles with spinel structure were synthesized by a chemical coprecipitation method with Poly?4-styrenesulfonic acid-co-maleic acid?sodium salt?PSSMA?.The results of XRD show that the synthesized MnFe₂O₄magnetic nanoparticles have a typical spinel structure,and the synthesized MnFe₂O₄magnetic nanoparticles have high content and good crystallinity.By X-ray photoelectron spectroscopy?XPS?analysis,the diffraction peaks of Fe,Mn,O and C elements are clearly shown in the spectrum.Since the prepared sample is placed in the air,a small amount of impurity N element appears,and no other impurity elements are found.Analysis of the XPS narrow scan pattern determined that the valences of Mn and Fe elements are 2+and 3+valence,respectively.It can be seen from the TEM images that the particle size of MnFe₂O₄ magnetic nanoparticles synthesized by adding PSSMA are mostly between 80⁹0 nm,with good dispersion and narrow grain size distribution.The magnetic properties of the VSM test show that the addition of PSSMA increased the saturation magnetization of MnFe₂O₄ magnetic nanoparticles from 22.79 emu/g to44.45 emu/g compared to the sample without PSSMA.?3?We synthesized MnFe₂O₄@SiO₂ magnetic nanocomposite particles with core-shell structure by adding tetraethyl orthosilicate?TEOS?.It can be seen from the TEM images that when the amount of TEOS added is only 0.05 mL,a thin layer of SiO₂ of about dozen nanometers is coated on the surface of the MnFe₂O₄ magnetic nanoparticles added with PSSMA to form a core-shell structure.As a whole,the obtained MnFe₂O₄@SiO₂ magnetic nanoparticles have uniform size and good dispersion,and the surface coating of SiO₂ is uniform and complete.The EDS spectra of MnFe₂O₄ magnetic nanoparticles added with PSSMA show that the main elements are Mg,Fe and O,and no other impurity elements are found.The main elements of the MnFe₂O₄@SiO₂ magnetic nano-powder coated with SiO₂ are Mn,Fe,Si and O,and no other impurity elements were found.Through the magnetic property test with VSM,we find that the saturation magnetization of the MnFe₂O₄ magnetic nanoparticles added with PSSMA before coating SiO₂ is 44.45 emu/g,which is almost equal to the saturation magnetization?43.59 emu/g?of MnFe₂O₄@SiO₂ magnetic nanopowder after SiO₂coating.However,by increasing the amount of TEOS added to 0.1 mL,the saturation magnetization of the MnFe₂O₄@SiO₂ magnetic nanopowder is greatly reduced due to the thickening of the cladding SiO₂,which is only 22.14 emu/g.