Study Of Magnetic Controlled Synthesis Of Nano-Fe₃O₄ And Its Composite Material Properties

Fe₃O₄ nanoparticles has been widely used in the preparation of magnetic fluids or as magnetic cores to magnetize functional materials due to its cheap and easy availability,superparamagnetism,and easy surface modification.The results show that the properties of nano-Fe₃O₄ materials are closely related to their particle size and micro-morphology,so it is of great significance to achieve the controlled synthesis of nano-Fe₃O₄.Considering the inherent magnetic moment of Fe₃O₄ molecules,the external magnetic field can induce the crystal growth process of Fe₃O₄ molecules,thus affecting the morphology of Fe₃O₄ nanoparticles.In this paper,an inverse co-precipitation method was used to synthesize nano-Fe₃O₄.In the synthesis process,uniform magnetic field and gradient magnetic field were applied to adjust and control the size morphology of nano-Fe₃O₄.Nano-Fe₃O₄ was prepared into magnetic fluid,and the difference of physical and chemical properties between Fe₃O₄ and conventional magnetic fluid,and the changes of conductivity,viscosity and wettability under the magnetization of magnetic field were studied.The magnetic chitosan adsorbent with high efficiency for solid-liquid separation was prepared by using the prepared nano-Fe₃O₄ as magnetic core,and its adsorption properties for dyes such as Congo red（CR）,methyl orange（MO）and methylene blue（MB）were studied.The specific research content of this paper is as follows:（1）Fe₃O₄ nanoparticles were synthesized by reverse co-precipitation method under applying magnetic fields of different properties.The morphology,structure and magnetism of Fe₃O₄ nanoparticles were characterized by transmission electron microscopy（TEM）,X-ray diffractometer（XRD）and sample vibration magnetometer（VSM）.The coating of nano-Fe₃O₄ by surfactant was measured by FT-IR.TEM images showed that the particle size of the synthesized nano Fe₃O₄ was more uniform than that of the conventional Fe₃O₄,but some nano-Fe₃O₄ were induced by the magnetic field to form rod-like structure.The higher the applied magnetic field intensity,the more rod-like Fe₃O₄ and the longer the rod length were induced.XRD and VSM spectra show that the nano-Fe₃O₄ synthesized under magnetic control has better crystallinity and stronger magnetism.The higher the intensity of the applied magnetic field,the better the crystallization of the nano-Fe₃O₄ and the stronger the magnetism.FT-IR spectra showed that oleic acid and Tween-80 were successfully double-coated on the nano-Fe₃O₄.（2）The magnetically synthesized nano-Fe₃O₄ was used as magnetic nanoparticles and double-coated with oleic acid and Tween-80 to prepare magnetically synthesized water-based ferrofluid.The conductivity,viscosity,wettability and other properties of the magnetically controlled synthesis of ferrofluid were measured and analyzed,and compared with the conventional ferrofluid.The magnetic fluid was magnetized in two types of magnetic fields,namely uniform magnetic field and gradient magnetic field,and the effects of magnetic field type,magnetization intensity and time on the conductivity,viscosity and wettability of the magnetic fluid were studied.The experimental results show that the conductivity and viscosity of the ferrofluid are better than those of the conventional ferrofluid,and the contact Angle on the hydrophilic glass material is smaller,indicating better wettability.After magnetization,the conductivity and viscosity of the magnetically controlled ferrofluid have been significantly improved,and the increase amplitude is also higher than that of the conventional ferrofluid.The magnetization effect of the uniform magnetic field is more obvious than that of the gradient magnetic field.The mechanism analysis shows that the morphology of magnetic nanoparticles and the arrangement of magnetic nanoparticles in the base liquid after magnetization have important effects on the properties of magnetic fluids.（3）CS/Fe₃O₄/GO magnetic adsorbent was prepared using the magnetically synthesized nano-Fe₃O₄ as magnetic core and chitosan/GO as carrier.TEM images showed that Fe₃O₄ and chitosan were bonded to GO.FT-IR and X-ray photoelectron spectroscopy（XPS）analysis further showed that nano-Fe₃O₄ and chitosan were chemically bonded to GO.VSM diagram shows that the synthesized CS/Fe₃O₄/GO magnetic adsorbent has strong magnetism and can realize efficient solid-liquid separation.The effects of p H value,initial dye concentration and contact time on the adsorption properties were studied.The experimental results showed that the maximum adsorption capacity of CS/Fe₃O₄/GO for MB,MO and CR were 210.6,258.6 and 308.9 mg/g,respectively.The adsorption kinetics and adsorption isotherm fitting indicated that the multi-dye adsorption of CS/Fe₃O₄/GO was a single molecular layer chemisorption.The enhancement of multi-dye adsorption may be closely related to the synergistic effect of CS and GO.The cycling test showed that the composite dye adsorption remained above90%after five cycles.Figure[39]Table[6]Reference[129]...