Synthesis and Catalytic Properties of Co,Fe and Zn Based Metal Oxide Composites

Author:Li Bao Ying

Supervisor:yu xiang yu xue lian


Degree Year:2019





Based on the research of photocatalytic degradation and electrocatalytic properties of cobalt,iron and zinc-based metal oxide composites,ZnO-ZnFe2O4nanomaterials were prepared by condensation reflux method.Graphene quantum dot modified ZnO-ZnFe2O4 composites were prepared by charge-induced assembly method.Using cobalt hexahydrate as the cobalt source,ZnxCo1-x-x Fe2O4 composites were successfully prepared with different Zn/Co ratios.The P element was doped to the Zn0.5Co0.5Fe2O4 composite by a simple heat treatment method.The main conclusion are as follows:(1)The graphene quantum dot modified ZnO-ZnFe2O4 composite prepared by condensation reflow method and charge-induced assembly method has enhanced light absorption efficiency from the smaller forbidden band width and high charge transfer efficiency and active sites number from the appropriate amount of graphene quantum dots,so it has excellent photocatalytic properties.In the MB photocatalytic degradation test,the degradation properties of 1GQD/ZnO-ZnFe2O4 were respectively10 and 4 times than ZnO and ZnO-Zn Fe2O4.In the photocatalytic degradation of tetracycline hydrochloride,the degradation efficiency of 1GQD/ZnO-ZnFe2O4 was more than 90%within 30 minutes.(2)Co3O4 nanocrystalline materials with different sizes and morphologies were successfully synthesized by simply controlling the concentration and type of metal precursors.Compared with Cubic-18 and Triangular-9,Cubic-9 Co3O4 nanomaterial shows higher ultimate current density(5.5 mA/cm2),corrected half-wave potential(0.48V vsRHE)and electron transfer process closer to 4(transfer electron number is3.68-3.79)in 0.1M KOH alkaline solution due to their larger specific surface area and high oxygen vacancy concentration..In addition,Cubic-9 type Co3O4 nanomaterial exhibits superior stability and resistance to methanol oxidation compared to commercial Pt/C catalysts.(3)The ZnxCo1-xFe2O4 composite was prepared by using terephthalic acid as an organic ligand and cobalt nitrate hexahydrate as a cobalt source.The OER and HER properties of ZnFe2O4、Zn0.7Co0.3Fe2O4、Zn0.5Co0.5Fe2O4、Zn0.3Co0.7Fe2O4 and CoFe2O4 were investigated in 1M KOH alkaline solution.With the decrease of Zn/Co ratio,the limiting current density tends to increase first and then decrease,and the overpotential(η10)also shows a trend of decreasing first and then increasing.When the Zn/Co ratio is 1,the Zn0.5Co0.5Fe2O4 composite exhibits excellent OER and HER properties,with the highest limiting current density,the lowest overpotential(OER:305 mV,HER:331 mV)and minimum Tafel slope(OER:131 mV/Dec,177 mV/Dec).The stability test results show that the material has good electrocatalytic OER stability and poor electrocatalytic HER stability,and the overpotential increases by about 300mV during the stability test.(4)The P-Zn0.5Co0.5Fe2O4 composite was prepared by doping the P element by heat treatment method.The electrocatalytic OER and HER properties of Zn0.5Co0.5Fe2O4and P-Zn0.5Co0.5Fe2O4 composites were compared in 1M KOH alkaline solution,it was found that P element doping can significantly improve the catalytic activity of the materials.Compared with Zn0.5Co0.5Fe2O4,the P-Zn0.5Co0.5Fe2O4 has higher oxygen vacancy concentration and electrolyzed water active sites(ECSA test results shows that the electrochemical specific surface area of P-doped materials is increased by89%.),exhibiting greater limiting current density,smaller overpotential(OER:277mV,HER:191 mV)and smaller Tafel slope(OER:44 mV/Dec,46 mV/Dec).The stability test result shows that the P-Zn0.5Co0.5Fe2O4 composite has excellent electrocatalytic OER and HER stability.