Preparation And Properties Of Magnetic Core-shell Nanocomposites

The components of core-shell nanostructures are combined together through physical or chemical action.The ordered assembly structure of core-shell materials exhibits excellent properties that single component does not possess.Core-shell materials extend its application in the fields of energy,environment and biomedicine.Furthermore,the magnetic core-shell structure nanomaterials not only have unique magnetic properties for easy recycling,but also have the characteristics of other components and synergistic effects.As a result,magnetic core-shell nanomaterials have attracted more and more attention from researchers.The control of composition,structure and size is the key to application of magnetic core-shell nanomaterials in the fields of nano-catalysis,adsorption,separation,etc.At present,the faced problem in materials science is to develop a simple,gentle and sustainable method to prepare core-shell nanocomposites with uniform dispersion,novel structure and excellent performance.This work aims to synthesize novel core-shell nanomaterials with uniform size,monodispersity and excellent performance.And,the relationship between structure and performance of catalysis,adsorption has been explored.Firstly,to solve the problem that noble metal nanoparticles are easily lost during the catalysis process,novel magnetic nanospheres?Fe3O4@RF-Pt@PDA?with sandwich-structure are prepared.The design of double-shell effectively restrains the aggregation and leaching of noble metal nanocrystals and improves the catalytic efficiency and stability of the catalyst.The as-prepared Fe3O4@RF-Pt@PDA nanocatalysts can be applied to quantitatively analyze the concentration of H2O₂ and glucose.Further increasing the loading of noble metal nanoparticles,simplify the synthesis path,the Fe3O4@SiO₂@?-AlOOH-Au@PDA magnetic nano-flower?MNF?is designed and synthesized.The Au@PDA hybrid shell can be formed by one-step method.As-prepared MNF shows excellent catalytic efficiency and cycling performance in 4-NP reduction.To further improve the structure and catalytis activity of nanocomposite,the yolk-shell structural magnetic catalyst with a large cavity is prepared and served as ideal nanoreactors for heterogeneous catalysis.Finally,combining the brilliant characteristics of mSiO₂ and PDA,mSiO₂/PDA with porous core-shell structure is prepared.mSiO₂/PDA exhibits excellent adsorption performance in the removal of U?VI?.The specific content includes the following aspects:1.Development of sandwich-structural magnetic nanospheres with ultra-small noble metal nanocrystals for the colorimetric detection of H2O₂ and glucose.A novel sandwich-structural magnetic microsphere?Fe3O4@resorcinol/formaldehyde resin-metal@polydopamine?is obtained,in which ultra-small noble metal nanocrystals can be sandwiched between the resorcinol/formaldehyde resin?RF?and polydopamine?PDA?layers.The PDA shell possesses a porous hydrogel-like inner structure,which not only effectively avoids the leaching of nanocrystals but also permits the permeation of substrate for catalysis.Fe3O4@RF-Pt@PDA possesses good peroxidase-like activity,which is dependent on pH and temperature,and the relevant catalytic kinetics follow the Michaelis-Menten behaviors.Moreover,Fe3O4@RF-Pt@PDA can be further applied for H2O₂and glucose detections and the limit of detection?LOD?is found to be as low as 3.1 ?M and 1.36 ?M,respectively.Benefiting from a facile preparation process,superior structure,and outstanding catalytic activity,these multifunctional microspheres possess high potential as artificial enzymes in clinical diagnosis,analytical chemistry and environmental fields.2.The structure design of flower-like magnetic nanocatalyst and its application in catalytic reduction of 4-nitrophenol?4-NP?.The Fe3O4 core is combined with hierarchical y-AlOOH to prepare Fe3O4@SiO₂@?-AlOOH with flower-like morphology.Then,the in situ redox-oxidation polymerization method is applied to form Au@PDA hybrid shell on the surface of matrix.The Fe3O4@SiO₂@y-AlOOH-Au@PDA?MNF?is obtained successfully.The thickness of SiO₂ layer,surface modification of Fe3O4 core and urea concentration are adjusted and controlled to explore the optimum synthesis condition.As-prepared MNF present excellent catalytic efficiency and cycling performance in 4-NP reduction,which can be ascribed to hierarchical y-AlOOH.The loading capacity and dispersity of Au nanoparticles are both improved.Furthermore,the one-step method of loading Au nanoparticles and forming PDA protective layer effectively protects noble metals nanoparticles from leaching during the catalytic process and simplifies the synthesis route.3.Investigation of fabrication and catalytic activity of yolk-shell structural magnetic nanocomposite.Yolk-like nanocomposites composed of superparamagnetic core and mSiO₂ shell are synthesized,in which functional nanocrystals?Pd,Au,Pt?are uniformly dispersed in the cavity.In yolk-like structure,hollow interior provides adequate space for catalytic reaction and magnetic core supplies a simple separation way for catalyst recovery.Moreover,the mSiO₂ shell effectively avoids the loss of noble metal nanocrystals and allows the efficient diffusion of reactants and products.The nanocomposites can be served as ideal nanoreactors for heterogeneous catalysis,and exhibit excellent catalytic activity and cyclic stability in both Heck reaction and 4-NP reduction.More importantly,this method can be extended to carry a variety of noble metal nanoparticles,which provides a reference for the preparation of magnetic yolk-like nanocatalysts.4.Preparation of porous core-shell nanosphere?mSiO₂/PDA?and study on its adsorption properties.Firstly,mSiO₂ nanospheres with uniform size and monodispersity are synthesized.Then mSiO₂ nanospheres are modified with PDA to obtain porous core-shell mSiO₂/PDA.Compared with pristine mSiO₂,mSiO₂/PDA shows excellent performance for removing U?VI?from aqueous solution.The maximum adsorption capacity of mSiO₂/PDA is 332.3 mg/g at 45? and pH=5.5.Meanwhile,the effects of experiment conditions on the adsorption properties of mSiO₂/PDA are explored.The investigation of adsorption behavior and mechanism will provide a new solution for preparing advanced adsorption materials.