Preparation And Catalytic Properties Of Magnetic Core-shell Nanocomposites

Industrial products such as paper,leather,and food will produce a large number of organic dyes,so the efficient treatment of organic dye wastewater is a major issue of environmental protection.Precious metals have become an efficient catalyst for organic reactions in recent years,but they have disadvantages such as poor dispersibility,poor stability,and difficulty in recovery.The smaller the nano-sized precious metal particles are,the easier they tend to agglomerate.Although the smaller the particle size,the more active sites there are,which can greatly improve the catalytic efficiency.However,the disadvantage of easy agglomeration gradually reduces the catalytic activity.Therefore,on the basis of the previous work,this paper uses magnetic material as the carrier,and the noble metal nanoparticles（NPs）are supported on the carrier by coordination or chelation.With the help of the magnetic force,the catalyst can be effectively separated from the reaction system after the reaction,so as to achieve the effect of recycling.Through the surface modification by the organic polymer or the silane coupling agent,the interaction between the loaded noble metal NPs with the modified support is enhanced,and it is difficult to fall off from the support,thereby improving the dispersibility of the catalyst.On this basis,three kinds of magnetic core-shell composite noble metal NPs were prepared by different modification methods,and their catalytic properties were deeply studied and the possible catalytic mechanism was speculated.The hydrogen production experiments show that the composite magnetic nanoparticles still have high stability and recyclability.（1）The magnetic CoFe₂O₄ submicrospheres as cores were prepared by a solvothermal method,and dopamine（DA）was polymerized on their surface under alkaline conditions to form CoFe₂O₄@PDA,because DA contains abundant amino and hydroxyl functional groups.Pt⁴⁺ions can be reduced to metal Pt NPs in situ and anchored on its surface to obtain core-shell CoFe₂O₄@PDA@Pt.The morphology,structure and magnetism of the samples were characterized by transmission electron microscopy（TEM）,X-ray diffraction（XRD）,vibrating sample magnetometer（VSM）and X-ray photoelectron spectroscopy（XPS）.Using inorganic dye potassium ferricyanate and organic dye p-nitrophenol as target pollutants to explore its catalytic activity,the results show that the degradation rate of potassium p-ferricyanate is over 95%and the degradation rate of p-nitrophenol is about 99.3%within 2min.（2）Magnetic CuFe₂O₄ nanoparticles modified by APTMS were also prepared by a similar way.Ethylene glycol was used as a reducing agent to reduce the precious metal Pd in situ.The presence of Cu（0）on the surface of CuFe₂O₄ can produce a synergistic effect with the precious metal Pd.The morphology,structure and crystal form of the samples were characterized by means of XRD,XPS,TEM and VSM.To explore the catalytic performance of p-nitrophenol（4-NP）and methyl orange as models of organic dyes.Both dyes were almost completely degraded within 10 min.The results show that the as-prepared CuFe₂O₄@NH₂@Pd is the highly efficient and magnetically separable catalyst.（3）Spinel-type magnetic material CuFe₂O₄ nanoparticles were prepared by solvothermal method,and were modified with 3-Aminopropyl trimehoxysilane（APTMS）through the amino group.A gold sol with a size of about 3 nm was adsorbed via coordination action to synthesize CuFe₂O₄@NH₂@Au.The morphology,structure and magnetic properties of the samples were characterized by TEM,XRD,XPS and VSM.The catalytic effects of CuFe₂O₄,CuFe₂O₄@NH₂ and CuFe₂O₄@NH₂@Au were compared respectively,and methyl orange and eosin were used as organic reaction models to evaluate the catalytic performance.The results showed that the degradation rates of methyl orange and eosin reached 98.1%and 95.7%within 15 min,respectively,which proved that the synergistic effect of CuFe₂O₄ and nano-Au particles has stronger catalytic activity than single catalysis,and its good catalytic performance provides theoretical guidance for the treatment of organic dye wastewater.