The Preparation And Properties Of AuAg Bimetallic Nanocomposites

With the in-depth development of nanoscience,precious metal nanomaterials have been widely used in the fields of biology,optoelectronics and catalysis,due to their unique optical,electrical,surface plasmon resonance and surface Raman scattering enhancements.Bimetallic nanocrystals not only have the electrical and thermal properties,but also have a unique crystal structure and morphology,which shows the excellent physical and chemical properties that single precious metals do not have.Therefore,the development of multifunctional multi-element precious metal nanomaterials has become one of the current research priorities.However,the surface energy of the precious metal nanoparticles is very high,and the bare particles are likely to aggregate and undergo secondary nucleation during the reaction.Therefore,it is of great scientific significance and practical value to develop simpler methods to prepare precious metal nanomaterials with stable structure and excellent performance.This subject takes AuAg bimetallic nanostructure as the research purpose,and uses the Galvanic replacement reaction principle between HAu Cl₄ and Ag to control the synthesis of two different shapes of AuAg bimetallic nanomaterials.The formation mechanism of AuAg bimetallic core-shell composite biomaterials was discussed,and the application prospects of AuAg bimetallic composite biomaterials in the fields of light,heat and catalysis were explored.The specific structure is as follows:（1）Summarize the research progress of precious metal nanocomposites.This article mainly introduces the classification and synthesis methods of precious metal composite nanoparticles and core-shell precious metal composite nanostructures in precious metal nanomaterials.It summarizes the main applications of precious metal nanocomposites in the field of biomedicine,and analyzes the importance of this research topic.（2）Development and optimization of AuAg@C bimetallic nanocomposite structure.The core-shell nanomaterial Ag@C was synthesized by an improved one-step hydrothermal method,and the substitution reaction between HAu Cl₄ and Ag was used to prepare Ag-AuAg@C core-shell nanospheres.Among them,the AuAg bimetallic nanocrystals are generated inside the C sphere and coated on the Ag core to form an Ag-AuAg hybrid nanocore.The acidic etching method is used to remove the remaining Ag crystals,and finally the AuAg@C bimetallic composite nanomaterial with carbon shell protection is finally obtained.In order to obtain the best product,this work also studied the effects of different reaction conditions,such as solvent（water or ethanol）,reaction temperature,concentration of HAu Cl₄,and hydrogen peroxide（with or without）on the final structure and morphology of AuAg@C.（3）Preparation and structure control of hollow structure AuAg@C@AuAg/PDA nanocomposites.Dopamine material was introduced into the replacement reaction system of HAu Cl₄ and Ag@C by a method combining displacement reaction and in-situ reduction polymerization.Using the self-polymerization characteristics of dopamine,hollow structure AuAg@C@AuAg/PDA nanocomposite microspheres were prepared.Among them,AuAg bimetallic nanocrystals are distributed on the core and shell,showing a uniform nano-framework-core and nanocrystal-satellite shell nanostructures.The study found that dopamine and Au（III）and Ag⁺in solution can be simultaneously oxidized and reduced on the surface of the carbon shell to form an outer hybrid shell（AuAg/PDA）of polydopamine（PDA）and AuAg bimetal.After etching the residual Ag,AuAg@C@AuAg/PDA core/shell nanomaterials with hollow structure are finally formed.Finally,the factors influencing the structure and composition of AuAg@C@AuAg/PDA composite nanomaterials are discussed,and the possible formation mechanism is proposed.（4）Research on photothermal and catalytic properties of bimetallic composite nano-biomaterials.On the basis of the above work,the photothermal effect of two bimetal nanomaterials,AuAg@C and AuAg@C@AuAg/PDA was first explored.The results show that both materials have good photothermal application potential and photothermal stability.At the same time,due to the excellent photothermal properties of the PDA itself,the hollow structure AuAg@C@AuAg/PDA nanocomposites show a wide range of application potential in the biological field.In addition,bimetallic nanomaterials are very important in the field of nanocatalysis.In this study,the catalytic performance of AuAg@C@AuAg/PDA was explored by using 4-nitrophenol as the model for the reduction of 4-nitrophenol.The results show that AuAg@C@AuAg/PDA has excellent catalytic and recycling performance.