Preparation And Application Of Magnetic Core-shell Materials

Currently, it is the increasingly serious problem of heavy metals and organicpollution in water. The synthesis easily separated recyclable adsorbent and catalyst isthe focus of scientific research in the sewage treatment process. The core-shellmaterial is a new composite material with adsorption and catalytic function. The basicstructural unit of core-shell material was determined by the kernel. Shell directlycontacting of the solution play the important physical and chemical properties such asadsorption, catalytic. These have been prepared by the various types of core-shellmaterials, these core-shell materials were widely used in the sewage treatment.In this paper, the iron oxide as a research object, different iron oxide magneticcore-shell materials were prepared. Preparation process does not require thesupporting role of the surface-active agents and organic solvents, the method wassimple, economic and environmental protection.The α-Fe₂O₃nanoparticles chemically stable, large surface area, catalyticproperties, have strong adsorption properties, such as adsorption of heavy metal ionsand organic; the Fe₃O₄nanoparticles are the good magnetic material, but itselveseasily occur reunion. we prepared α-Fe₂O₃as the shell and Fe₃O₄as nuclear toproduce the Fe₃O₄/α-Fe₂O₃core-shell materials. The α-Fe₂O₃coated on the surface ofthe Fe₃O₄nanoparticles, through steric stabilization of this material can be uniformlydispersed in the solution, which can be separated and recovered in the appliedmagnetic field conditions.Content and results of this thesis:（1）The particle size of about20-30nm Fe₃O₄nanoparticles were prepared by Theco-precipitation method and precipitated oxide, dispersion in the outer layer coatedferrihydrite,then using of Fe²⁺catalytic phase transformation of ferrihydrite intoα-Fe₂O₃nanoparticles to prepared the core-shell structure typical Fe₃O₄/α-Fe₂O₃nano-structure composite materials. The composition, structure and morphology ofthe core-shell materials were charactered by FT-IR, FESEM, TEM, UV-Vis, BET andXRD. The results show that: the size of the core-shell structure of the Fe₃O₄/α-Fe₂O₃ nano particles are about40-80nm and have good degree of crystallization.（2） We have researched the adsorption performance of Cr₂O₇^2-,Cr³⁺with theFe₃O₄/α-Fe₂O₃core-shell material in the K₂Cr₂O₇、Cr （NO3）3solution which wereregarded as the adsorbate and the factors such as pH, ionic strength, dosage amount ofadsorption were considered. The results show that: the Fe₃O₄/α-Fe₂O₃nanoparticlesadsorbed Cr⁶⁺the best at pH3.5, the optimum dosage of6g/L and the maximumadsorption capacity was the6.932mg/g, in this time the adsorption isotherms followedthe Langmuir isotherm model; The Fe₃O₄/α-Fe₂O₃nanoparticles adsorbed Cr³⁺optimum at pH value of4.5, the optimum dosage of10g/L and the maximumadsorption capacity was the33.344mg/g,in this time the adsorption isothermsfollowed the Freundlich isotherm model.（3） The adsorption of chromium in the core-shell material was irreversibleadsorption charactered by the Langmuir parameters and adsorption-parsing isotherm,.The heavy metal ions could be desorbed with the appropriate desorbent resolution.For the Cr⁶⁺,the best desorbent agent was the0.5mol/L NaOH solution and theresolution rate was99.7%; for the Cr³⁺,the best desorbent agent was the0.1mol/LH₂SO₄solution with the resolution rate of82%.（4） In the H₂O₂/（Fe₃O₄/α-Fe₂O₃） system, we conducted the study of the catalyticdegradation of methylene blue at pH=9with the degradation rate of95.49%.（5） We used the different methods to prepare the Fe₃O₄/Ferrihydrite core-shellmaterials and studied the adsorption properties. Fe³⁺as the reactant, Ferrihydritemixture was prepared at room temperature as Fh1; Ferrihydrite prepared in hightemperatures as Fh3; Fe²⁺as the reactant, the hydrated iron oxide was regarad as Fh2.Cr⁶⁺adsorption effect in order to: Fe₃O₄/Fh2> Fe₃O₄/Fh3> Fe₃O₄/Fh1; The adsorptioneffects of Cr³⁺: Fe₃O₄/Fh1> Fe₃O₄/Fh2≈Fe₃O₄/Fh3.