Preparation Of Porous Ferric Oxide Micro-nanostructures And Their Photocatalytic Properties

The abundance of iron element in the crust is ranked among the top five in all elements and thereby the cost of iron oxides is low.At the same time,the types of iron oxide are multifarious.The common iron oxide compounds,including Fe3O4,?-Fe2O3 and ?-Fe2O3,are environmentally friendly and have high stability.Therefore,the iron oxides show great potential applications in catalysis,lithium-ion batteries and biological field.Porous iron oxide micro-and nano-materials have magnetism and high specific surface area,both of which are highly desired for pollutant degradation,adsorption separation,catalysis,and bio-drug delivery.Hence,the development of preparation methods that can produce iron oxide compounds simply,fast,and in large-scale attracts extensive research.The content of this thesis is based on porous Fe3O4 micro-and nano-materials,and mainly contains the following two parts:In the first part,I developed a preparation method for porous Fe3O4 micro-nanostructures and studied their photocatalytic performances.In the preparation,Au nanospheres are employed as the sacrifice template.Fe3O4 nucleates and grows on the surface of gold nanospheres.At the same time,since the nano-sized gold can be etched with ferric ions,the growth process is accompanied by the etching of gold nanospheres.Growth and etching processes accompany mass transfers,that is,trivalent iron ions diffuse to the surface of gold nanospheres,and the etched gold ions are diffused into the solution.The mass transfer leads to the formation pore channels within Fe3O4 and finally gives rise to porous Fe3O4 micro-and nano-spheres.As the amount of Au nanospheres is increased,the nanocrystal size of the mesoporous Fe3O4 microspheres gradually becomes larger,and the surface of the microspheres gradually transformed from uneven to smooth.The gap between the nanocrystals in the surface of the mesoporous Fe3O4 microspheres gradually first becomes larger and then becomes smaller with the increase of the amount of Au nanospheres.When the amount of gold nanospheres is fixed,the reduction of the amount of the Fe precursor produces microspheres with grooves on the surface and irregular Fe3O4 structures.The photocatalytic activity of porous Fe3O4 micro-nanospheres was studied by using photocatalytic degradation of RhB as a model reaction.The results show that the porous Fe3O4 nanospheres have good photocatalytic activity and stability.In the second part,in order to further improve the photocatalytic performance of Fe3O4 nanostructures,the noble-metal@Fe3O4 core@shell hybrid structure was designed and prepared.In such hybrid nanostructures,the photocatalytic performance of Fe3O4 can be enhanced by the surface plasmon resonance in the noble metal cores.It is found that the oxidation-reduction potential of noble metal ions plays a crucial important role for the formation of core@sheIl hybrid nanostructures.When the oxidation-reduction potential of noble metal ions is higher than that of ferric ions,the core@shell hybrid nanostructures can be formed.However,when the oxidation-reduction potential of the ions is lower than that of ferric ions,the core@shell hybrid nanostructures cannot be produced.As a result,both Ag and Au can form core@shell hybrid nanostructures with Fe3O4,while Pd cannot.Moreover,the molar ratio between noble metal and iron source is also important to the formation of core@shell nanostructures.When Ag/Fe molar ratio is 0.15-0.30,the produced Ag/Fe3O4 has a core@shell structure.When it is increased to 0.60,the core@shell structure cannot be formed anymore.The prepared Ag@Fe3O4 nanostructures have clear surface plasmon resonances,which can be utilized to increase the light absorption of Fe3O4 shells and thus improve their photocatalytic performance.