Controllable Preparation And Magnetic Properties Of Fe₃O₄ Nanoparticles

As an important magnetic functional material,Fe₃O₄nanoparticles have become a research hotspot in the field of magnetic nanomaterials due to their unique anti-spinel structural and magnetic properties.Compared with other magnetic nanomaterials,Fe₃O₄nanoparticles have the advantages of good biocompatibility,high saturation magnetization,non-toxicity,simple preparation process and low cost,and are widely used in targeted drug carriers,magnetic resonance imaging,and magnetic heat treatment,magnetic recording materials,catalysts,lithium-ion batteries,water treatment and other fields.With the development of nanotechnology,the preparation methods of Fe₃O₄nanoparticles are constantly innovating,but in order to achieve its controllable preparation and production applications,there are still many urgent problems to be solved,such as low saturation magnetization,low yield,poor reproducibility,tedious technology and long production cycle.In this paper,a new preparation method of Fe₃O₄nanoparticles,one step reduction method,is proposed.By adding excess citric acid in the sol-gel process,the precursor's low-temperature combustion decomposition and organic carbon thermal reduction reaction can be completed simultaneously,and the Fe₃O₄nanoparticles can be synthesized by one-step reduction.The feasibility of the experiment and the ratio of reactants were predicted by thermodynamic analysis and theoretical calculation of propellant thermochemistry.By controlling the carbothermal reduction temperature,holding time and the ratio of explosive agent in the reaction,the controllable preparation of Fe₃O₄nanoparticles was realized at 450?650°C.Fe₃O₄nanoparticles with 3?20 nm,monodisperse,spherical and narrow particle size distribution were synthesized by changing the cooling method and adding dispersant ammonium citrate.The size and temperature dependence of magnetic properties were systematically investigated.The saturation magnetization(M_s)of Fe₃O₄nanoparticles synthesized by one-step reduction method is significantly higher than other chemical synthesis methods such as co-precipitation,hydrothermal and microemulsion methods.The highest M_sreaches 93.02 emu/g,which is close to the M_sof bulk Fe₃O₄;Coercive force H_c,residual magnetization(M_r)and squareness ratio decrease with the increase of grain size D.The zero field cooling-field cooling(ZFC-FC)curve measured the metal-insulator transition(Verwey transition)point of T_v=128 K for Fe₃O₄.The hysteresis loop measurements at5 K,128 K and 300 K show that the hysteresis behavior is significantly reduced with increasing temperature,and M_sat 128 K is the highest.The H_c,M_rand magnetocrystalline anisotropy constant K,decrease as the increase of temperature.This method has the advantages of high saturation magnetization,simple operation,short preparation period and high controllability.It not only enriches the preparation technology of nanomaterials and the basic theory of biomagnetic nanomaterials,but also provides some theoretical guidance and technical support for the development of targeted drug delivery carriers and magnetic adsorbents.