In Situ Study Of Growth Modulation And Mechanism Of Spinel-type Zinc Ferrite

As one of magnetic materials,ferrites have been widely applied in different fields,such as catalysis,magnetic storage media,biomedicine.Shape,size,and structure can affect chemical and physical properties of the materials.Superparamagnetic materials usually show a low magnetization value because of nanosized particles,which limits their practical applications.So to improve magnetization value for these materials becomes a key issue.In this paper,zinc ferrite(ZnFe2O4)with high saturation magnetization and different morphology(cluster,nanosheets,monodisperse nanoparticles)have been prepared by changing the molar ratio of Fe to Zn or adding ligand.The mechanism for ZnFe2O4 formation has been investigated through in situ microcalorimetry.The study would provide the theoretical guidance and scientific basis for the development of superparamagnetic spinel nanomaterials with high saturation magnetization.At the same time,ZnFe2O4/ZnO magnetic composites were synthesized through one-step method by addition of EDTA.The main works are listed as the following:1.Zno.2Fe2.8O4 clusters were selected as the aiming sample for the investigation on the cluster formation mechanism.In situ microcalorimetry was used to explore the mechanism for the cluster formation.And different characterization techniques were used,such as XRD,ICP-AES,TEM,XPS and FTIR.The experimental results showed that Fe(OCH2CH2OH)3 first formed through a reaction between Fe3+ and HOCH2CH2OH in the system,the Fe3+ contained in the as-formed Fe(OCH2CH2OH)3 was replaced by Zn2+ to form Zn(OCH2CH2OH)2.Polymerizations occurred between Fe(OCH2CH2OH)3 and Zn(OCH2CH2OH)2,which induced a gelator formation.When the experimental temperature increased,the H-bondings were destroyed,and the gel was transferred to a solution.During the process,ethylene glycol molecules were replaced by H2O molecules and the-OCH2CH2O-groups were as bridges to bond with different cationic ions.Cluster-shaped(Fe,Zn)OOH was synthesized when the substitution was end.Cluster-shaped ?-Fe2O3 was formed when the cluster-shaped(Fe,Zn)OOH dehydrated.Then,the cluster-shaped Zn0.2Fe2.8O4 was synthesized through a transition of the cluster-shaped ?-Fe2O3.Coordinating ions as[Fe(EDA)3]3+ and[Zn(EDA)3]2+ were formed in the reaction system with the addition of EDA,which may prevent the polymers formation,further showed that the group-OCH2CH2O-bridge played a key role in the cluster formation.The study on the formation of magnetic nanoclusters will provide the thought and theoretical basis for the development of this type of material,and provide experimental basis for similar scientific problems.2.Monodispersed Zn-doped Fe3O4 magnetic nanosheets with high magnetization and surface area were synthesized by a facile one-step solvothermal method.The Zn-doped Fe3O4 magnetic nanosheets formation mechanism was studied in details using an in-situ calorimetric method.And different characterization techniques were used,such as XRD,ICP-AES,XPS,FTIR and TEM.The complexes formation,as[Fe(EDA)3]3+ and[Zn(EDA)3]2+,deceased free Fe3+ and Zn2+ concentrations,which prevented some reactions,and induced some reactions to occur at higher temperature.At the same time,the(111)facets of the Zn-doped Fe3O4 became stable,which induced the nanosheets formation.These results demonstrated that the EDA can change the sample formation mechanism.The Zn-doped Fe3O4 nanosheets with large saturation magnetization and high surface area show potential applications in different fields such as adsorption,biomolecular separations,and drug targeted delivery.3.ZnFe2O4/ZnO magnetic materials with high surface area were synthesized by a facile one-step solvothermal method.The formation mechanism was studied in details using an in-situ calorimetric method.The complexes,Fe3+-EDTA and Zn2+-EDTA,deceased free Fe3+ and Zn2+concentrations,which prevented the formation of metal alkoxide.Meanwhile,suitable EDTA as ligand can be adsorbed on the surface of the crystal,so that the nuclei would assemble into a ball in the role of amino and carboxy,similar with-OCH2CH2O-bridge in the second chapter.The prepared ZnFe2O4/ZnO magnetic composites show potential applications in terms of adsorption and photocatalysis,because of large specific surface area and good dispersibility.