Preparation And Properties Of PI/Fe₃O₄ Composite Microspheres

Magnetite?Fe₃O₄?is one of the oldest magnetic materials,and the material has been widely used in applications such as chemicals,environment,electronics and biomedicine due to its high saturation magnetization,biocompatibility,cheap and low toxicity properties.However,naked magnetite nanoparticles are easy to agglomerate and are easily oxidized in air,lets its application has been limited in some areas.In recent years,the protection of Fe₃O₄ has been widely concerned by researchers,constructed a core-shell structural magnetite hybrid nanoparticles using the organic or the inorganic are exceptionally promising protection strategy.Polyimide has excellent heat resistance and mechanical properties,and a polymer with a specific function can be obtained by designing a special monomer structures.Polyimide coated Fe₃O₄ can effectively improve the thermal stability of the microspheres,and the structure design can give composite microspheres with different functional.However,to the best of our knowledge,there are no reports in the literature of the polyimide coated Fe₃O₄.Preparation of Fe₃O₄ core-shell microspheres in traditional methods all need pre prepared Fe₃O₄ particles,then the organic or inorganic coated onto the surface of Fe₃O₄.There are few studies on prepared Fe₃O₄ core-shell microspheres by one-step reaction system.In this paper,we present a facile one-step solvothermal method for preparation of PI/Fe₃O₄ composite microspheres using poly?amic acid?triethylamine salts and Fe³⁺as raw materials,and the formation mechanism of the PI/Fe₃O₄ composite microspheres has been investigated.And the effect of morphologies and properties of PI/Fe₃O₄ composite microspheres by polyamic acid triethylamine salt concentration,reaction temperature and reaction time were discussed.The structures of the samples were characterized by infrared spectroscopy?IR?and X-ray diffraction?XRD?.The characteristic absorption peak of PI and the characteristic absorption peak of Fe₃O₄ appeared in the IR spectra of PI/Fe₃O₄ composite microspheres,which indicated that PI was successfully encapsulated in Fe₃O₄.And through the analysis of XRD,the Fe₃O₄was found to exist in the cubic phase of the inverse spinel structure.The stability of Fe₃O₄ can be improved by coated PI onto the surface of Fe₃O₄ through the thermal gravimetric curve of Fe₃O₄.The results show that,pure Fe₃O₄ has a high saturation magnetization?79.28 emu/g?.The amount of PI coated with different concentrations of Fe₃O₄ is different,the more the concentration the more coated with,and the saturation magnetization is smaller.The reaction temperature and reaction time have important influence on the magnetic properties,the reaction temperature is low or the time is short,the saturation magnetization of the product will be reduced.But high temperature or long time will caused the PI to be digested,which seriously affects the morphology of the composite microspheres.By comparing the experimental results of the optimum process conditions were obtained:the concentration of 4.5 wt%,200?and 8 h.The microspheres have good morphology under these conditions,high saturation magnetization?35.33 emu/g?and polyimide containing 54.35 wt%.In this paper,the Cu²⁺adsorption of the products was carried out.The results showed that the adsorption capacity of PI/Fe₃O₄ composite microspheres and pure Fe₃O₄ on Cu²⁺was basically the same.The number of free carboxyl groups on the surface of PI/Fe₃O₄ composite microspheres was increased by KOH solution hydrolysis,which can greatly improve the adsorption capacity,the adsorption capacity of the microspheres increased from 10.56 mg/g to28.84 mg/g.