Synthesis And Properties Of Rare Earth-Doped CaCO₃@SiO₂ Composites

Due to the excellent performance of both shell and core,core-shell materials can not only optimize their own performance,but also carry out functional design of materials by surface modification.There are great advantages of core-shell materials based on the advantages in surface modification,functionality and stability.Among many core-shell materials,Ca CO₃@Si O₂core-shell has become the focus of this paper because of its porous Si O₂shell and various crystalline Ca CO₃core.As a kind of common doping materials,rare earth elements are widely used in many fields due to their unique and excellent physical and chemical properties.Based on the extensive application and excellent effect of rare earth doping in core-shell materials,in this paper,rare earth elements are doped and modified with Ca CO₃@Si O₂core-shell materials.Two kinds of rare earth doped Ca CO₃@Si O₂core-shell composite materials were prepared:1.By doping rare earth elements with Ca CO₃and coated with Si O₂,the core-shell composite Ca CO₃:Eu³⁺@Si O₂is synthesized.The properties of the material were characterized by XRD,FTIR,SEM,TEM and TG analysis.The obtained material contained the characteristic peaks of both Ca CO₃and Si O₂.Si O₂.In addition,the hydroxyl group of Si O₂and partial vacancy make the material a potential adsorbent.By applying the material to the adsorption of Tb³⁺,the adsorption behavior was studied,and the fitted with a variety of adsorption models.The quasi-second-order model showed better fitting effect,while the Weber-Morris model interpreted the rate control step of the adsorption process,indicating that the adsorption of Tb³⁺by the composite was a single-layer chemisorption process.The fitting results with various kinetic models prove that the adsorption of Ca CO₃:Eu³⁺@Si O₂on Tb³⁺is a monolecular layer and favorable chemisorption process.Under the condition of 323K and p H 5.83,the maximum adsorption capacity of Tb³⁺is188.26 mg·g^-1,which becomes a beneficial attempt in the field of adsorption of rare earth doped core-shell materials.2.Interfacial energy transfer of core-shell structure plays an important role in material luminescence.A series of Ca CO₃@Si O₂core-shell materials doped with Eu³⁺and Tb³⁺were designed and synthesized based on the luminescence properties of rare earth elements.The structure,phase composition and morphology of the samples were characterized by XRD,FT-IR,TGA,SEM and TEM analysis.Single doping Eu³⁺,single doping Tb³⁺and double doping Eu³⁺,Tb³⁺core-shell materials were synthesized to investigate the the luminescent properties and energy transfer process.The optimal double doping concentration of the materials was explored by comparing the excitation,emission spectrum intensity and the fluorescence lifetime.According to the CIE chromaticity diagram,the luminescent color of the material changes from green to yellow,orange to finally red following with the changing of doping concentration.This kind of core-shell materials provides a reference for the application in field of fluorescence luminescence.