Preparation And Magnetic Characterization Of Fe₃O₄ Nanoparticles And Nanofilms

Fe₃O₄ nanomaterials, which have good magnetic and electric properties, is a potential candidate for information materials, wave absorbing materials, targeted drug carrier and Giant Magnetoresistance (GMR) devices. In this paper, Fe₃O₄nanoparticles and nanofilms were prepared by ultrasonic codeposition method, template method and electrodeposit method. Fe₃O₄ nanoparticle films were obtained with electrostatic self-assembly technique. The influencing factors, growth mechanism and related properties of these Fe₃O₄ nanomaterials were investigated by TEM, SAED, SEM, AFM, XRD, IR, UV-vis and VSM.Fe₃O₄ nanoparticles were prepared with ultrasonic codeposition method. The effect of ultrasonic power on nanoparticle size and specific saturation magnetization were studied. The Fe₃O₄ nanoparticles prepared under ultrasonic field were more uniform and with higher saturation magnetization. When ultrasonic power reached 200W, the Fe₃O₄ particles of 45-50 nm were obtained with good dispersion, and the sample was superparamagnetic with its specific saturation magnetization being 86.19 emu/g.Carboxymethylchitosan used as coating agent, the stable Fe₃O₄ magnetic fluid with uniform-size particles was firstly prepared by one-step oxidative hydrolysis method. The effects of temperature and the concentrations of Fe²⁺ and carboxymethylchitosan on nanoparticle size and system stability were investigated. Besides, the mechanism of carboxymethylchitosan stabilizing Fe₃O₄ magnetic fluid was put forward. When the concentrations of Fe²⁺ and carboxymethylchitosan were both 1×10-4 mol/L, the single-crystal spheral Fe₃O₄ nanoparticles with 10nm could be obtained, and the magnetic fluid system was quite stable.Fe₃O₄ nanoparticle films were prepared by electrostatic self-assembly technique on mica and coverslip for the first time. The films morphologies and magnetic properties along with assembly time were tested. Because the charge density on coverslip modified with CTAB was higher than that of mica modified with Mn²⁺, and Fe₃O₄ nanoparticles coated with carboxymethylchitosan was easily adsorbed with CTAB, the Fe₃O₄ nanoparticles were more compact on coverslip than on mica.The Fe3O4 films were firstly prepared by in-situ oxidative hydrolysis on chitosan, and the formation mechanism of Fe3O4 film was also proposed. Under lower temperature(such as 30℃), network structured film was obtained with 50-100 nm net-aperture and 30 nm net-wall thickness. Under higher temperature(such as 50℃and 80℃), the products were compact particle films. The particle sizes of Fe3O4 obtained at 50℃and 80℃were about 25 nm 30 nm. Besides, Fe3O4 films were prepared on chitosan film cross-linked with Glutaraldehyde, and the effects of cross-link degree on the films morphologies were studied.Electrodeposition of Fe3O4 film technique was improved, and Fe3O4 films were obtained in conventional electrodeposition cell. The effects of electrode potential, the concentration of Fe2+, temperature and pH on the deposition rate and the morphology of Fe3O4 film were investigated. The mechanism of electrodeposition of Fe3O4 film was studied from the view of electrochemistry.