Fabrication And Magnetic-optical Properties Of Fe₃O₄-based Nanocomposites

Bifunctional magnetic-optical nanocomposites have potential applications in drug delivery,fluorescence imaging,magnetic particle testing and other fields.This dissertation took Fe₃O₄ nanoparticles as magnetic source,ZnS,Eu and Tb as fluorescent materials.The fabrication technology and properties of Fe₃O₄-based magneto-optic nanocomposites were systematically investigated,and the influence of morphology,composite and fluorescent materials on magnetic-fluorescence properties were analyzed,and magnetic marks of the magnetic particles were discussed.1)Fe₃O₄ nanoparticles with two different shapes were prepared by chemical co-precipitation method and hydrothermal process.The growth mechanism of Fe₃O₄nanospheres was studied and the effects of hydrothermal conditions on the size and magnetic property of Fe₃O₄ nanoparticles was analyzed.?1?It was found that the structure inducers have great effect on the size and morphology of the resulted Fe₃O₄nanospheres in the NaHCO₃ with Na₂CO₃ system.A wide size distribution of Fe₃O₄nanospheres was obtained at 0.397mol/L NaHCO₃.The morphology of the products transformed from nanospheres to small particles of about 25 nm with many holes on the surface.The solvothermal time and FeCl₃·6H₂O amount have great influence on crystalline and morphology of Fe₃O₄ nanospheres.?2?Some spheres became bigger from 700 to 800 nm with more hole on the surface in the presence of NaAc·3H₂O with FeCl₃·6H₂O of 0.148mol/L and the reaction time extending from 12 to 20 h,which is agreement with the basic principle that the radius is proportional to the cube root of reaction time.When the content of FeCl₃·6H₂O was 0.018 mol/L,the solid Fe₃O₄nanospheres transformed to hollow with almost the same size with the time extending from 12 to 16 h.?3?The effects of three different cooling methods?the furnace cooling,air cooling and ice-water cooling?on the structure,size and magnetic properties of Fe₃O₄ nanospheres were studied.The cooling rate affects significant the dissolution of the small spheres in the Ostwald process,and thus eventually influences the growth of big spheres.Among three different cooling methods,it was found that the ice-water cooling can obtain the Fe₃O₄ nanospheres with the minimum size and most dense spherical particles,and the maximum saturation magnetization can reach as high as99.033 emu/g,while furnace cooling leads to the maximum size of Fe₃O₄ nanospheres,and the saturation magnetization reduces to 82.6193 emu/g.2)The bifunctional magnetic-optical Fe₃O₄@ZnS core-shell nanospheres were fabricated.It was found that the amount of TAA can not only control the size of Fe₃O₄@ZnS core-shell nanospheres,but also adjust the magnetic-fluorescent intensity of the nanospheres.When the amount of TAA increased from 0.044 to 0.089 mol/L,the size of nanospheres grew from 590 to 690 nm,and meanwhile the corresponding magnetism reduced,and fluorescence intensity gradually increased.The strongest emission peak of the nanocomposites is at 358 nm due to the transition of the S vacancy and the saturation magnetization decreased from 61.66 emu/g to 58.85 emu/g because of the increased nonmagnetic ZnS content.3)AredandgreenemissionofFe₃O₄@Eu?DBM?₃Phenand Fe₃O₄@Tb?DBM?₃Phen magnetic-fluorescent nanocomposites were prepared by doping rare earth elements of Eu and Tb into Fe₃O₄ nanospheres respectively.With increasing the concentration of rare-earth elements,the luminescence intensity increases while the magnetism reduced to 7.93 emu/g and 15.6 emu/g,respectively.Excited at 395 nm wavelength,Fe₃O₄@Eu?DBM?₃Phen shows an emission peak at 618 nm.Fe₃O₄@Tb?DBM?₃Phen shows characteristics of Tb³⁺emission peak situated at 514 and537 nm,and a blue light emission peak at 431 nm.4)Bifunctional magnetic-optical Fe₃O₄/ZnS composite was prepared via two-step chemical method,and the effect of Co-doped on the bifunctional magnetic-optical properties was analyzed.It was found that the nonmagnetic ZnS luminescent material significantlyreducesthesaturationmagnetizationintensityofFe₃O₄/ZnS nanocomposites.Co doping can improve the saturation magnetization of Fe₃O₄/ZnS composites with the maximum emission peak at 477 nm.5)The magnetic mark characteristics of Fe₃O₄ nanoparticles were studied.The magnetic mark feature of artificial crack testing block of magnetic nanofluids was compared with a conventional magnetic fluids,and it was found that the magnetic mark of the nanofluids is clearer and longer than that of conventional fluids.Coating thickness of the artificial testing block and the shape of Fe₃O₄ have a great influence on the magnetic particle testing.The flake Fe₃O₄ fluids displaying the crack on the artificial testing block is clearer than that of the spheres Fe₃O₄ fluids after withdrawing the external magnetic field.Fe₃O₄@Eu?DBM?₃Phen composites also have an excellent property of defect magnetic trace.