Synthesis Of Yolk-Shell Structure Ag@SiO₂ Composite Particles With Adjustable Cavity Size And SERS Performance

Ag nanoparticles(NPs)exhibit excellent electrical,optical and catalytic properties because of its small size effect,surface effect and unique local surface plasmon resonance(LSPR)characteristics.But Ag NPs are easily to aggregation,difficult to separate,and chemical unstability in practical application.In general,forming a protect layer on the surface of Ag NPs can stabilize the Ag NPs.Silica is widely used due to its excellent chemical stability and optical permeability.Core-shell structural Ag@SiO2 composite particles stabilized the Ag NPs,but closed the active sites on the surface of Ag NPs.Compared with the core-shell structural Ag@SiO2 composite particles,the hollow structure formed by the Yolk-Shell structural Ag@SiO2 composite particles can not only increase the specific surface area of Ag NPs,but also make Ag NPs have more active sites.Moreover,it can provide limited reaction space for Ag NPs,and can improve the catalytic and optical properties of Ag NPs.Ag NPs have been widely used in SERS detection because of their unique LSPR properties,high signal enhancement and easy preparation.The existence of shell of Yolk-Shell structure not only stabilizes the Ag NPs and makes them have stable LSPR properties,but also can anchor and adsorb more probe molecules,and produce more "hot-spot".Based upon the above research background,a method of synthesizing Yolk-Shell structural composite particles with controllable hollow size is proposed in this study.Based on Ag NPs coated with silica,Yolk-Shell structural Ag@SiO2 composite particles were prepared by oxidation etching of potassium persulfate(KPS).In this method,the structure and LSPR properties of Yolk-Shell structural Ag@SiO2 composite particles can be controlled by controlling the amount of KPS.At the same time,Yolk-Shell structural Ag@SiO2 composite particles with amino-functionalized can be obtained by simple modification.The SERS properties of Yolk-Shell structural composite particles with different structures were studied by using p-aminothiophenol(4-ATP)and 4-mercaptobenzoic acid(4-MBA)as probe molecules.This thesis mainly carries out the following two aspects of research work:(1)In this thesis,a synthesis method of Yolk-Shell structural composite particles with adjustable hollow size is proposed.The SiO2 coating layer was formed by hydrolysis and condensation of TEOS on the surface of Ag NPs,and the Yolk-Shell structural Ag@SiO2 composite particles were synthesized by selective etching of KPS.It is found that Ag@SiO2 composite particles with different shell thickness can be obtained by changing the amount of TEOS,and the maximum absorption peak of the composite particles is red-shift obviously with the increase of shell thickness.Compared with core-shell structural Ag@SiO2 composite particles,the hollow size of Yolk-Shell structural Ag@SiO2 composite particles can be controlled by changing the amount of KPS.The partial oxidation etching of Ag NPs and the formation of cavity lead to blue-shift of the maximum absorption peak of Yolk-Shell structural Ag@SiO2 composite particles.Compared with core-shell structural Ag@SiO2 composite particles,Yolk-Shell structural Ag@SiO2 composite particles show enhanced SERS performance for 4-ATP.Moreover,the hollow structure is larger,and the SERS performance of the composite particles is better.This is due to the fact that the hollow structure of Yolk-Shell structural Ag@SiO2 composite particles can enrich more 4-ATP.At the same time,the Ag NPs with lager specific surface area can anchor and adsorb more probe molecules,and it is easy to produce more "hot-spot".It can provide a larger electromagnetic field coupling effect,and has a stronger SERS effect.(2)Based on the easy functionalization of SiO2,the modified Yolk-Shell structural Ag@SiO2 composite particles were designed and synthesized.The specific sensing to the probe molecule could be realized by using the specific linkage between the shell and the target molecule.Yolk-Shell structural Ag@SiO2-NH2 composite particles were synthesized by using(3-aminopropyl)trimethoxysilane(APTMS)as modifier at room temperature.The results show that compared with the unmodified Yolk-Shell structural Ag@SiO2 composite particles,the amino-functionalized Yolk-Shell structural Ag@SiO2-NH2 composite particles exhibit a significantly enhanced Raman effect for 4-MBA,which is due to the fact that the presence of amino groups on the shell surface facilitates the bonding of more probe molecules.At the same time,the hollow structure can enrich more probe molecules.The synthesis of surface functionalized Yolk-Shell structural Ag@SiO2 composite particles will be of great value in sensing,catalysis and other fields.