Synthesis And Adsorption Researches Of Spinel-type Ferrites Nanoparticles And Chitosan-matrix Magnetic Carriers

Recently, nanometer spinel-type ferrites, as important nanometer magnetic materials, have attracted huge attention due to their unique magnetism, electricity and optics properties along with wide applications in magnetic targeted, magnetic adsorption and magnetic separation fields. However, several properties are required for the application in the above outlined several fields:they must be small in diameter and good in dispersibility, and must have functional groups of loading drug, radionuclide or metal ions. Therefore, controlled synthesis and modification of nanometer spinel-type ferrites have drawn continuous and worldwide research attention. In this dissertation, valuable explorations have been carried out on the preparation and modification of nanometer spinel-type ferrites along with metal ions adsorption aspect of modified carriers, especially in metal ions adsorption mechanism of magnetic carriers.In chapter 2, spinel-type CoFe₂O₄, ZnFe₂O₄, Co_0.5Zn_0.5Fe₂0₄ and Fe₃O₄ nanoparticles were prepared by relatively facile low temperature solid state method and chemical co-precipitation method, respectively, and were characterized. Uniting test results, the magnetism origin and their magnetic characteristics were discussed and analyzed, and the reasons of presenting superparamagnetism for ZnFe₂O₄ and Fe₃O₄ nanoparticles different from block materials were interpreted. Through comparing with the saturated magnetization of above outlined spinel-type ferrites nanoparticles, CoFe₂O₄ nanoparticles were chosen as magnetic core and low temperature solid state method chosen as synthesis method.In chapter 3, to solve the problem of particle agglomeration widely existing in traditional low temperature solid state synthesis of CoFe₂O₄ nanoparticles and enhance dispersibility of resultants, new methods, salt-assisted low temperature solid state method and PVA-assisted low temperature solid state method through introducing of inner inorganic salt NaCl or dispersant PVA in precursor mixtures were come up. Firstly, the effects on the phase, dispersibility and morphology of the resultants for NaCl and PVA addition amount and calcined temperature were investigated, respectively. The results indicated that the D_XRD of the as-prepared CoFe₂O₄ nanoparticles at optimal condition was 16.1nm and 16.7nm, and the surface area was 101.12m2/g and 68.74m²/g, respectively, it can be seen that the surface area increased apparently and the degree of agglomeration decreased apparently compared with the as-prepared CoFe₂O₄ nanoparticles via traditional low temperature solid state method. Secondly, the reaction mechanism of salt-assisted and PVA-assisted low temperature solid state synthesis of CoFe₂O₄ nanoparticles was discussed. Finally, the possible influence mechanism on particles dispersibility and morphology of NaCl and PVA was studied.In chapter 4, magnetic chitosan, magnetic N-site chitosan and magnetic O-site chitosan were prepared using the high dispersive CoFe₂O₄ nanoparticles prepared by salt-assisted low temperature solid state method as magnetic core and using chitosan as modifying based materials. First of all, using glutaraldehyde as crosslinking agent, magnetic chitosan which using crosslinking chitosan as coating layer was prepared via traditional emulsion crosslinking method. Next, using 1-Ethyl-3-(3-dimethyllaminopropyl) carbodiimide hydrochloride (EDAC) as zero-length crosslinking agent, through acylating C-2 site-NH₂ of chitosan, magnetic N-site chitosan which using EDTA-chitosan and DTPA-chitosan as hybrid coating layer, respectively, was prepared. Lastly, magnetic O-site chitosan was prepared through carboxymethylating C-6 site—OH of chitosan, anhydriding of carboxymethyl chitosan and alcoholysis reacting of anhydrided-chitosan, in turn. Thus, three kind of magnetic carriers using chitosan as based materials were prepared.In chapter 5, firstly, the contrastive research of adsorption properties of three kind of magnetic chitosan carriers prepared in chapter 4 was carried out using heavy metal ions Cu²⁺and Ni²⁺ as adsorption object, respectively. The results indicated that the adsorption properties of magnetic N-site chitosan using chitosan-chelating agent (EDTA/DTPA) hybrid materials as modifying materials were best, magnetic O-site chitosan were next and magnetic chitosan were last. Secondly, aiming at the actuality that the research of magnetic chitosan carriers mostly concentrated on preparation, less research on adsorption properties, and much less research on adsorption mechanism, the adsorption mechanism of three kind of magnetic chitosan carriers for heavy metal ions was studied, uniting the analysis results of IR and XPS, the functional groups of participating in chelating were confirmed, the adsorption model was put forward, and the results indicated that the adsorption mechanism of magnetic chitosan was similar to NN-type chelating agent, and that magnetic N-site chitosan and magnetic O-site chitosan were similar to N·O-type chelating agent.