Controllable Syntheses Of Ferrite Based Nanocomposites And Their Catalytic Performance

Nanocomposites,combining multiple functionalities of their composites,has attracted more and more attention.Effects of nanostructures on their properties and selective growth phenomenons in the syntheses of nanocomposites needed to be studied.Herein,controllable syntheses and transformations of Ag-Mx Fe3-xO4(M=Co,Mn)nanocomposites were firstly studied.Then,the relationships between structures and catalytic performances were investigated through the analyses of their catalytic performances.Meanwhile,selective growth disciplines were studied via the characteriztion of their sulfidition processes.The main results were as follows:(1)Ag@MxFe3-xO4 core-shell nanoparticles were firstly synthesized via a seed-mediated method and then loaded onto Vulcan XC-72 carbon.As-prepared Ag@MxFe3-x O4/C futher thansformed to hollow-MxFe3-xO4/C through the oxidation and diffusion of silver in saturated NaCl solution.Catalytic performances of these nanocomposites on the oxygen reduction reaction(ORR)were analyzed in alkaline media.As a result,Ag@MxFe3-xO4/C exhibited superior ORR catalytic activities and electronic conductivity over hollow-MxFe3-xO4/C.It was proposed that the existence of Ag improved their electron conductivity and the electronic coupling between Ag core and MxFe3-xO4 shell enhanced their ORR catalytic activities.(2)Ag-MFe2O4 heteromeric nanoparticles were firstly synthesized via a seed-mediated method and then loaded onto Vulcan XC-72 carbon.As-prepared Ag-MFe2O4/C futher thansformed to MFe2O4/C through the oxidation and diffusion of silver in saturated Na Cl solution.Component removed from the Ag-MFe2O4 heteromers to obtain MFe2O4/C and Ag+MFe2O4/C.Catalytic performances of these nanocomposites on the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER)were analyzed in alkaline media.As a result,Ag-MFe2O4/C demonstrated highest catalytic activity for ORR.The direct coupling and electron transfer between Ag and MFe2O4 in heteromer nanoparticles were proposed to enhance their electro-catalytic activities.Ag-MFe2O4/C also exhibited good stability and methanol tolerance.Thus,Ag-MFe2O4/C were potential non-Pt candidates with bi-functional electro-catalytic activities for ORR and OER.(3)Selective growth disciplines were studied through analyses of sulfidation and thansformation process of Ag-CoFe2O4 core-shell and heteromeric nanoparticles.As to the formation mechanism of sulfidation product,it was discussed with the hard and soft acids and bases law.Besides,magnetic and optical properties of sulfidation products were charecterized.As a result,CoS/Ag2S-hollow-Fe2O3 nanocomposites showed good photoluminescence properties and superparamagnetic properties at room temperature.