The Controllable Synthesis And Study On Magnetic Properties Of Iron Oxide-based Nanorods And Nanoparticles

Magnetic nanomaterials,as an important branch of functional nanomaterial,have received extensive attention and research because of their tremendous ly interesting magnetic properties and potential applications in nanoscale.According to the value of coercive force,magnetic material can be divided into hard magnetic material and soft magnetic material.Magnetic nanoparticles have many special magnetic properties that are different from those of bulk materials,such as high coercivity,superparamagnetism,low Curie temperature and so on,which are mainly determined by the surface effect and the small size effect.In addition,coercivity and saturation magnetization are not only related to the crystal structure of the nanoparticles,but also to their size,morphology,chemical composition and dispersity.Nano-iron oxide is a very promising inorganic non-metallic functional material,with low cost,non-toxic,strong corrosion resistance,nature abundance,multiple valence states and other characteristics.Because of acceptable magnetic properties and high stability,it can be widely used in magnetic storage,magnetic recording,electromagnetic absorption,biomedicine,negative electrode material of supercapacitor,gas sensor,energy catalysis,etc.In this paper,we first synthesized hematite and akagenite nanoparticles via hydrothermal process at 120oC with ferric chloride as precursor and CTAB as surfactant.The morphology,structure and magnetic properties of hematite and akagenite were studied by means of Field emission scanning electron microscope?SEM?,X-Ray Diffraction?XRD?,Electron diffraction spectroscopy?EDS?and Vibrating sample magnetometer?VSM?.The morphology and size of the crystal can be controlled by changing the concentration of the precursor.When the concentration of ferric chloride is relatively low,the rhombic,spherical and cubic shaped hematite nanoparticles were synthesized.When the concentration of ferric chloride is high,we got akagenite nanorods with different aspect ratio.The akagenite nanorods were calcined at different temperature to obtain hematite nanorods with different size.And the magnetic property was characterized in order to investigate the effect of calcining temperature on phase transition.Finally,the obtained hematite nanorods were reduced with H₂ at different temperature so that Fe,Fe₃O₄ and Fe₂O₃@Fe₃O₄ composite were obtained.Secondly,spherical cobalt ferrite nanoparticles with high saturation magnetization and high coercivity were fabricated with ferric chloride and cobalt chloride as precursors,CTAB as surfactant and urea as complexing agent.We explored the effects of complexing agent,precursor concentrations,reaction temperature,reaction time,ultrasonication,external magnetic field on the morphology,structure and magnetic property of the products that were characterized by SEM,EDS,XRD and VSM.In the end,we obtained spherical cobalt ferrite nanoparticles whose diameters are 60 nm under the optimal condition that the concentration of ferric chloride,cobalt chloride,urea is 0.04 M,0.02 M,0.6 M respectively,reaction temperature is 150oC,reaction time is 12 h and ultrasonic time is 0.5 h.The coercivity reaches 3.57 kOe,and the saturation magnetization is 34.743 emu·g-1.