Preparation Of Bimetallic Composites Based On Polyelectrolyte Membrane Modulation And Their LSPR Properties

Due to as the ultra-high sensitivity,less consumption and fast nondestruction,Surface-Enhanced Raman Scattering(SERS)has a very important application in the field of analysis and detection.The local electromagnetic field enhancement,generated by the localized surface plasmon resonance(LSPR)of noble metal(Ag,Au,Cu,etc.)nanoparticles,can significantly enhance the Raman signal;besides the LSPR property is also effectively regulated by the composition,size,morphology and dielectric environment of metal nanoparticles.The construction of SERS-active substrate with high sensitivity,excellent stability and repeatability is one of the important research topics in this field.The two-dimensional colloidal crystals with ordered structure not only exhibit unique optical properties,but also is widely used as a template for preparing ordered structure materials,which can ensure the uniformity and repeatability of materials.The two-dimensional structure nano-AgAu bimetallic composite material with high periodicity and uniformity can be used to construct a high sensitivity,stability and reusable SERS-active substrate,because it not only inherits advantages of Ag and Au nano-metals,but also has good plasmon coupling and synergistic effect.Based on the above research background,this thesis innovatively proposes the strategy for preparing two-dimensional AgAu bimetallic composite materials through the method of polyelectrolyte.By using core-shell microgel particles as basic building units,two-dimensional colloidal crystals template can be prepared by the method of air-liquid interfacial self-assembly.In this study,the positively charged polyallylamine hydrochloride(PAH)and negatively charged polyacrylic acid(PAA)were selected to prepare the polyelectrolyte film through a layer-by-layer assembly(LBL)method.Due to the electrostatic interaction between nano-metal precursor salt and the amino and carboxyl groups,the film can effectively regulate the morphology of metal nanoparticles and stabilize them.In order to investigate the effects of the composite structure of polyelectrolyte film and the concentration of precursor solution on the structure,the composition and LSPR properties of the prepared AgAu bimetallic composite material were systematically studied.Meantime,the pH-responsive of polyelectrolyte film can realize the regulation of LSPR property of metal nanoparticles.In this work,we aim to construct a SERS active substrate with uniform structure,high stability and reusability.This thesis mainly carries out the following three parts in this research work:(1)The PAH/PAA polyelectrolyte film with layers of alternating structure were prepared by a LBL method,and the polystyrene@polyacrylic acid(PS@PAA)microgel particles,as basic building units of the two-dimensional colloidal crystals,were synthesized by a two-step polymerization method.The Au nanolayer with a regular structure was obtained by the convenient and easy-controllable ion sputtering method,denoted as the composite of PAH/PAA-PS@PAA-Au.The optical properties of two-dimensional Au composite materials were controlled by changing the thickness of Au nanolayer and using the pH-responsive of polyelectrolyte chain.As the result,the Au nano-layer presented a 'hat' structure.Along with the thickness of the Au layer increases,the plasmonic coupling peak was blue-shifted from 680 nm to 665 nm.In addition,by changing the pH,the charge of the PAH and PAA chain structure promoted the swelling or deswelling of the PAH/PAA film,so that the optical properties of the composite material can be regulated by change of refractive index caused by the change of the thickness of the polyelectrolyte film.(2)The AgAu bimetallic composite materials with two-dimensional structure were prepared by assembling the polyanion and polycation electrolyte film(PAH/PAA)assembled by the LBL method.The PS@PAA-(PAH/PAA)-Au bimetallic composite materials were prepared by galvanic replacement reaction using colloidal crystals as template and silver nanolayer obtained by ion sputtering as sacrificial template.These research results showed that the pore structure of AgAu composite particles prepared by assembling PAH film were mainly distribute at the junction of template microgel particles;after assembling the PAA film,the pore structure extended to the surface of PS@PAA particles.The surface pore structure of the bimetallic composite material prepared by assembling PAH/PAA film disappeared.With the increase of the number of PAH/PAA layers,the LSPR maximum absorption peak of LSPR was red-shifted from 485 nm to 496 nm.In addition,the optical properties was also controlled by the swelling or deswelling effect of the PAH/PAA film,which was casued by changing the pH in this environment.(3)The composite polyelectrolyte(PEC-(PAH-PAA))film was formed by the LBL method with composite polyanion and polycation electrolytes was used to control the preparation of two-dimensional structure AgAu bimetal composite material.Through the electrostatic interaction between the polyelectrolyte layer and the metal precursor and its skeleton structure to adjust the replacement reaction of silver and HAuCl4,the control of the AgAu bimetallic composite structure was achieved.The research results showed that the 'hat' structure of AgAu composite material prepared by assembling the PEC-(PAH-PAA)had a more uniform distribution,compared to the PAH/PAA.As the polyelectrolyte layer increased,the LSPR maximum absorption peak was red-shifted from 484 nm to 496 nm.By changing the pH,the charge of the PAH and PAA chain caused the thickness of the PEC-(PAH-PAA)film to change,and the optical properties of the composite material were controlled by the change of refractive index.Using 4-mercaptobenzoic acid(4-MBA)as probe molecule,the SERS properties of Ag and AgAu composite materials with PEC-(PAH-PAA)were investigated.The results showed that the signal intensity of PS@PAA-Ag(PEC-(PAH-PAA))and PS@PAA-Ag(PEC-(PAH-PAA))Au composite materials had decreased.Along with the increase of polyelectrolyte layer,the Raman signal intensity of Ag composite material had increased,which was attributed to the electrostatic interaction between the polyelectrolyte film and the probe molecule;Besides,the signal intensity of AgAu bimetallic composite material was decreasing with the increase of nano-Au.In addition,the stability and reusability of the composite materials need further studied.