Modification And Application Of Fe₃O₄ Nanoparticles Based On Self-stabilized Precipitation Polymerization

Ferroferric oxide magnetic nanoparticles（Fe₃O₄MNPs）have attracted intensive attentions due to the advantages of small size,large specific surface area,good biocompatibility and superparamagnetism.However,the pristine magnetic particles suffered from the shortcomings of weak oxidation resistance and poor dispersion stability,leading to severe aggregation during application.Even worse,there are lack of functional groups on the surface of Fe₃O₄MNPs,which cannot meet the requirement of high-performance and multi-functionalities for practical application.Therefore,in order to overcome the above disadvantages,the surface modification is required to grant Fe₃O₄MNPs with desired functionality and special properties,which can largely broaden their application fields.In this paper,a polymer coating layer was facilely and high-efficiently constructed on the surface of Fe₃O₄MPNPs through self-stable precipitation polymerization（2SP）,attaining surface functional modification of the Fe₃O₄MPNPs.Magnetic composite microspheres with good magnetic properties,strong oxidation resistance and versatile surface functionalities were successfully prepared,and their application as magnetic support for catalysts as well as the corresponding catalytic performance were investigated in detail.The main content of this work is as follows:1.Three kinds of Fe₃O₄MPNPs with different morphology,particle size and surface functional groups were prepared by co-precipitation and hydrothermal methods.The obtained Fe₃O₄MPNPs were firstly modified with silane coupling agents to improve their dispersibility and oxidation resistance,and Fe₃O₄@Si O₂particles containing reactive surface vinyl groups were formed.Thereafter,an anhydride functional polymer shell layer was directly constructed on the surface of Fe₃O₄@Si O₂through 2SP process.2.The properties of the as-prepared Fe₃O₄composite particles were comprehensively evaluated with regards to morphology,size,crystal structure and magnetic properties.The experimental results showed the spherical Fe₃O₄MNPs with an average particle size of 264 nm were prepared by hydrothermal method in the presence of PEG2000.After being sequentially modified with tetraethoxysilane（TEOS）and KH-570 silane coupling agent,Fe₃O₄@Si O₂with surface vinyl groups were obtained.Through 2SP copolymerization of divinyl benzene（DVB）and maleic anhydride（MAH）,DVB-MAH cross-linked polymer network（PDM）were in situ formed on the surface of Fe₃O₄@Si O₂,leading to the formation of Fe₃O₄@Si O₂@PDM magnetic composite particles（420 nm）with the best comprehensive properties.The influence of monomer concentration,core-shell mass ratio,reaction temperature and time on the size and morphology of the obtained Fe₃O₄@Si O₂@PDM were investigated systematically to optimize the polymerization conditions.3.Well-dispersed Pd nanoparticles with a diameter of 5 nm were in situ formed and loaded on the surface of Fe₃O₄@Si O₂@PDM magnetic microspheres prepared under optimal conditions,using Pd（OAc）₂as Pd precursor and sodium borohydride（Na BH₄）as the reducing agent.The composition,morphology,size and magnetic properties of the as-prepared Fe₃O₄@Si O₂@PDM-Pd were characterized in detail by TEM,FT-IR,XPS,XRD and VSM.4.The reduction reaction of 4-NP was selected as benchmark reaction to evaluate the catalytic activity of the resultant Fe₃O₄@Si O₂@PDM-Pd catalyst,and the apparent reaction rate constant k_appwas measured to be 2.31×10^-2s^-1,indicating high catalyst activity.The effects of solvent,Pd loading content and Na BH₄concentration on the catalytic performance of the as-prepared Fe₃O₄@Si O₂@PDM-Pd was investigated in detail.The experimental results showed that,the Fe₃O₄@Si O₂@PDM-Pd obtained in 25%ethanol at Pd/microspheres mass ratio of 1:20 exhibited the best catalytic performance,and the optimum Na BH₄concentration was 5 m M.The stability and reusability of the Fe₃O₄@Si O₂@PDM-Pd was assessed by repeated catalytic reactions,and the conversion rate of 4-NP is still above 88%after 10 repeated catalytic cycles,demonstrating excellent stability and reusability.