Study On Preparation And Electrochemical Properties Of Fe₃O₄ Based Core-shell Nanocomposites

In this paper,the Fe₃O₄@SiO₂@vmSiO₂ microspheres with ordered mesochannels and inter-lamellar void were successfully prepared through stepwise solution-phase interface deposition.Firstly,Fe₃O₄ nanoparticles were obtained using the solvothermal method,and Fe₃O₄ nanoparticles were coated with SiO₂ by a Sto?ber method to form Fe₃O₄@SiO₂ nanoparticles.Secondly,resorcinol-formaldehyde?RF?resins were precipitated onto the Fe₃O₄@SiO₂ surface to form Fe₃O₄@SiO₂@RF nanoparticles.The Fe₃O₄@SiO₂@RF nanoparticles were further coated with hexadecyltrimethylammonium chloride aggregation as the template,tetraethylorthosilicate as the silica precursor.Finally,Fe₃O₄@SiO₂@vmSiO₂microspheres with mesochannels and inter-lamellar void were successfully prepared by removing RF and CTAC through high temperature treatment.The resulting Fe₃O₄@SiO₂@vmSiO₂ microspheres possess ordered mesopore channels with a diameter of approximately 6.8 nm in the outer shell and an inter-lamellar void of approximately 30 nm between the inner shell and the outer shell.Laccase?LAC?was immobilized on a modified Fe₃O₄@SiO₂@vmSiO₂ microsphere by covalent attachment to obtain the matrix materials and stabilized onto the glassy carbon electrode?GCE? surface to form Fe₃O₄@SiO₂@vmSiO₂-LAC/GCE.Using Fe₃O₄@SiO₂@vmSiO₂-LAC/GCE as the working electrode and 0.1 mol L^-1 PBS?pH6.0?as electrolyte,the three-electrode system was used to detect dopamine?DA?.The proposed biosensor exhibits excellent electrocatalytic performance for dopamine with a linear range of 1.5⁷5?mol L^-1 and low detection limit of 0.177?mol L^-1?S/N=3?.The biosensor can be used to determine DA in the presence of potentially interfering substances without significant interference,indicating that the biosensor has a higher selectivity for DA.Furthermore,Fe₃O₄@C@MnO₂ microspheres were successfully fabricated via a multi-step route,and used it as electrode material for supercapacitors.First,use the same method as above to prepare Fe₃O₄@SiO₂@RF nanoparticles.Then,Fe₃O₄@C nanoparticles were obtained by carbonizing the Fe₃O₄@SiO₂@RF nanoparticles under N₂ condition and etching the SiO₂ shell by NaOH solution.Finally,the carbon layer surface was coated with a shell of MnO₂ through a facile redox reaction between carbon and KMnO₄ to form Fe₃O₄@C@MnO₂ microspheres.The resultant Fe₃O₄@C@MnO₂microspheres showed a typical core-shell structure with distinct magnetite core,10 nm inter-lamellar void,a 30 nm thick carbon layer in the middle layer,and a 50 nm thick MnO₂ shell at the outer layer.To investigate the electrochemical performance of the material,the resulting Fe₃O₄@C@MnO₂ microspheres were used as working electrodes for supercapacitors with 0.1 mol L^-1 Na₂SO₄ as the electrolyte.The three-electrode system was used.The results show that the Fe₃O₄@C@MnO₂ electrode exhibits superior electrochemical performance.Fe₃O₄@C@MnO₂ electrode shows a specific capacitance of 158 F g^-1 at high current density of 0.5 A g^-1,high specific capacitance of 110 F g^-1 at high current density of 20 A g^-1.This indicates that the Fe₃O₄@C@MnO₂ electrode has excellent rate performance.The cycling stability of the Fe₃O₄@C@MnO₂ electrode was tested at 2 A g^-1.The results show that after 2000cycles of charge and discharge,the specific capacitance retention rate is still 89.7%.The above results show that Fe₃O₄@C@MnO₂ microspheres has great potential in supercapacitor applications in the future.