Synthesis And Magnetic Properties Of ZnFe₂O₄@SiO₂ And ZnCo₂O₄@SiO₂ Nano-particles With Core-shell Structures

Nowadays,with rapid development of the nanotechnology,a single preparation of nano-materials is not the hot spots of today's material research.In recent years,the nano-materials researches focus on the nanocomposites.In order to meet the actual needs,kind of special functional nano-composite materials become a hot research.Among many nanocomposites,the magnetic nanocomposites with core-shell structure have attracted the attention and in-depth exploration of many domestic and foreign researchers due to their unique structures and properties.There are many types of spinel-like magnetic oxides like AB₂O₄.Many of the magnetic oxides have unique physical and chemical properties such as superparamagnetism,high coercivity,high resistivity and catalytic properties.At the same time,silica?SiO₂?also has many special advantages:preventing the interaction of magnetic particles,good stability,good biocompatibility.In addition,Silica shell also has a good hydrophilicity and acid resistance.AB₂O₄@SiO₂ core-shell structure magnetic nanocomposites are likely to be applied to future magnetic therapies for the treatment of cancer.Therefore,the synthesis and application of core-shell structure AB₂O₄@SiO₂ magnetic nanocomposites have been attracted more and more attentions.For the spinel structure of the magnetic oxide,ZnFe₂O₄ and ZnCo₂O₄ are more special class of magnetic oxides,because of high resistivity,the synthesis process is simple,short synthesis cycle and lower preparation costs,etc.In this paper,we try to synthesize ZnB₂O₄@SiO₂?B=Fe or Co?magnetic nanocomposite particles by"two-step" method.First,the pure phase ZnFe₂O₄ and ZnCo₂O₄ magnetic nanocomposites are synthesized by simple hydrothermal and chemical coprecipitation method respectively.And then,the composite ZnB₂O₄@SiO₂ magnetic nanoparticles were prepared by hydrolysis of orthosilicate?TEOS?.The main contents of the experiment are as follows:Synthesis and magnetic properties of ZnFe₂O₄@SiO₂ core-shell structure magnetic nanoparticles.The pure phase ZnFe₂O₄ magnetic nanoparticles were synthesized with Zn?NO₃?₂·6H₂O and Fe?No₃?₃·9H₂O as experimental materials by adjusting the pH of the mixed liquid with sodium hydroxide?NaOH?solution and using deionized water as the solvent.The ZnFe₂O₄@SiO₂ nanocomposite was prepared by the hydrolysis of ethyl orthosilicate?TEOS?magnetic nanoparticles.The following experimental data were tested with:X-ray diffraction?XRD?,Raman spectroscopy,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,high resolution transmission electron microscopy?HRTEM?and vibrating sample magnetometer?VSM?.At the same time,magnetic nanoparticles?ZnFe₂O₄ and ZnFe₂O₄@SiO₂?were required to anneal at different temperatures to explore the magnetic properties and magnetic stability of nanoparticles.The results show that the particle size of ZnFe₂O₄ and ZnFe₂O₄@SiO₂ nanoparticles are between 10-15 nm and the shape of the particles is irregular.And the ZnFe₂O₄ and ZnFe₂O₄@SiO₂ magnetic nanoparticles show the paramagnetic properties.The ZnFe₂O₄ magnetic nanoparticles still exhibit paramagnetic characteristics at different annealing temperatures?even at temperatures below 800 ??.At the same time,ZnFe₂O₄@SiO₂ core-shell nanocomposite particles exhibit paramagnetic properties at temperatures up to 580 ?,which indicates that the ZnFe₂O₄ and ZnFe₂O₄@SiO₂ magnetic nano-particles have good magnetic stability.Preparation and magnetic properties of ZnCo₂O₄@SiO₂ magnetic nanoparticles with core-shell structure.ZnCo₂O₄ magnetic nanoparticles were synthesized with Zn?NO₃?₂·6H₂O and Co?NO₃?₂·6H₂O as the reaction raw materials by adjusting the pH of the mixed liquid with sodium hydroxide?NaOH?solution and using anhydrous ethanol as the solvent.The ZnCo₂O₄ composite was prepared by the hydrolysis of ethyl orthosilicate?TEOS?SiO₂ magnetic nanoparticles.X-ray diffraction?XRD?,Raman spectroscopy?SEM?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and vibrating sample magnetometer?VSM?analysis show that ZnCo₂O₄ and ZnCo₂O₄@SiO₂ exhibit good magnetic nanoparticles.ZnCo₂O₄ and ZnCo₂O₄@SiO₂ magnetic nanoparticles have a particle size of about 20 nm and the shape of the particles is different.In order to explore the magnetic properties and magnetic stability of magnetic nanoparticles,the samples?ZnCo₂O₄ and ZnCo₂O₄@SiO₂?annealed at different temperatures is needed.As a result,the ZnCo₂O₄ and ZnCo₂O₄@SiO₂ magnetic nano-particles exhibit paramagnetism.The ZnCo₂O₄ magnetic nanoparticles still exhibit paramagnetism at different annealing temperatures?even at temperatures up to 1050 ??.At the same time,it was found that the core-shell structure ZnCo₂O₄@SiO₂ nanocomposites appeared to exhibit"ferromagnetic" characteristics,even at temperatures as high as 550 ?.This shows that the ZnCo₂O₄ and ZnCo₂O₄@SiO₂ magnetic nano-particles have good magnetic stability.Based on the above experimental results,the preparation process of spinel-type magnetic nanoparticles ZnB₂O₄ and ZnB₂O₄@SiO₂ is simple,the preparation cycle is short,the core-shell structure is easy to form,and also has paramagnetic and magnetic stability.Dispersibility is not so ideal.In the future experimental study,we can further optimize the synthesis method and add dispersants and surfactants to improve the dispersion between particles and the formation of a more desirable core-shell structure.