Solvothermal Synthesis And Modification Of Fe₃O₄ Microspheres And Their Adsorption And Catalytic Properties

Magnetic materials have gained worldwide attention in recent years due to their applications in many areas,such as adsorption,catalysis,magnetic separation and drug delivery.Magnetic adsorbents and magnetic catalysts have been reported in many literatures.However,there are only few reports about magnetic materials with both superior adsorption and catalytic properties.In this thesis,solvothermal synthesis of monodisperse Fe₃O₄ magnetic microspheres of ca.0.34 ?m in ethylene glycol?MEG?was first optimized.Then epichlorohydrin?ECH?-modified Fe₃O₄ magnetic microspheres were prepared by one-step solvothermal synthesis in MEG or by post-synthetic modification.The great adsorption and catalytic properties of the ECH-modified Fe₃O₄ microspheres were respectively demonstrated by the adsorption of Cu²⁺ and the selective oxidation of benzyl alcohol to benzaldehyde.The main results and conclusions of this thesis are as follows:1.The effects of various parameters on solvothermal synthesis of Fe₃O₄ magnetic microspheres were optimized.The Fe₃O₄ magnetic microspheres have been successfully synthesized by heat treatment of the concentrated mixture of FeCl₃·6H₂O?13.7 mmol?,NaOAc?43.9 mmol?and MEG?9 mL?at 198 oC for 14 h.After being washed and dried,1.018 g of the product can be obtained with the yield of 96%.The product was characterized by XRD,SEM and VSM to be pure Fe₃O₄ magnetic microspheres of ca.0.34 ?m,which is suitable for the application of magnetic separation technology.This formula of Fe₃O₄ magnetic microspheres significantly reduces the production cost and organic waste.2.ECH-modified Fe₃O₄ magnetic microspheres were prepared by one-step solvothermal synthesis in MEG.The product was pure Fe₃O₄ magnetic microspheres as characterized by XRD,SEM,and VSM.The adsorption property of ECH-modified Fe₃O₄ microspheres was studied by the absorption of Cu²⁺ from aqueous solution.ECH/Fe initial molar ratio has a great influence on Cu²⁺ adsorption.When it was 0.8,the maximum adsorption reached 17.5 mg·g-1.In addition,the addition of 2.5 wt%NaCl significantly increased the adsorption capacity?17.5 mg·g-1 vs 28.5 mg·g-1?.After being recycled seven times,it maintained proximately 90% of the original Cu²⁺adsorption capacity.The study of the adsorption kinetics and thermodynamics indicated that the apparent activation energy was 14.7 kJ·mol-1.The adsorption process was endothermic?11.8 kJ·mol-1?,but the increase of the entropy?56.8J·mol-1·K-1?resulted in the reduction of the Gibbs free energy.As such,the adsorption of Cu²⁺ was a spontaneous process.3.ECH-modified Fe₃O₄ microspheres exhibited higher catalytic activity for the selective oxidation of benzyl alcohol with H₂O₂ to benzaldehyde than blank Fe₃O₄microspheres?benzaldehyde yield: 34% vs.8%?.The used ECH-modified Fe₃O₄ catalysts could be easily recovered with a magnet,and have been recycled five times without significant loss of activity after being regenerated by NaBH₄?0.3 M?reduction and ECH modification.The kinetic study of H₂O₂ catalytic decomposition and theoretical calculations revealed that the ECH modification promoted the adsorption of H₂O₂ on the surface of Fe₃O₄ by hydrogen bonding,and increased the collision frequency between H₂O₂ molecules and Fe₃O₄ by about 10 orders of magnitude,which facilitated the decomposition of H₂O₂ and the formation of hydroxyl radicals for selective oxidation of benzyl alcohol to benzaldehyde.