Synthesis And Chracterization Of Bimetallic Nanostructures

As we all know,a bimetallic nanostructure composed of two different elements with a certain alloying method and geometric structure exhibits physical and chemical properties that are superior to single metal nanoparticles,so it exhibits many meaningful properties and more extensive of applications.For example,precious metal nanoparticles such as gold,platinum,palladium have outstanding catalytic performance.After introducing elemental elements such as silver and copper into the precious metal catalytic system both reduces the catalyst cost o and enhances the catalytic activity due to the synergistic effect between the two metals.Therefore,in this paper we mainly prepared core-shell gold-silver composite nanostructures and gold-copper composite nanostructures using gold nanoparticles as templates,and prepared silver nanoparticles with different morphologies.The catalytic properties of different composition of bimetallic nanoparticles and silver nanoparticles with different morphology were studied from electrochemical catalysis to chemical catalysis.The main research contents and results include:1.The core-shell structure of gold nanorods@silver（AuNR@Ag）with different morphology was prepared by using gold nanorods（AuNRs）as precursor,and the catalytic activity of this core-shell structure in the electrocatalytic oxidation of formaldehyde was studied.First,gold nanorods@silver core-shell structures with different morphologies were prepared using purified and unpurified gold nanorods as templates.After comparing the characteristics of the two products,the control effect of the residual gold precursor in unpurified gold nanorods was proposed to control of the formation of shuttle-like nanostructures.Then,a new synthetic route was designed to prepare the shuttle-like AuNR@Ag-Au core-shell nanostructures with different morphologies,which verified the control effect of the gold precursor in forming the shuttle-like of core-shell structure.Finally,the electrocatalytic performance of AuNR@Ag-Au bimetallic nanostructures with different shells in the electrochemical oxidation of formaldehyde were studied,and the effect of scanning rates on the catalytic reaction and the relationship between the scanning speed and the corresponding current peak were analyzed.The results of the composition of shell metal elements on the catalytic activity showed a typical bimetallic synergistic effect.It is proved that the catalyst containing a small amount of gold has the highest catalytic activity,which is about 10 times that of other different shell structures.The surface reaction process of formaldehyde oxidation catalyzed by metal was proposed.2.The core-shell structure of gold nanobipyramid@silver with different morphologies was prepared by using gold nanobipyramid as precursor,and their catalytic activities in the reduction of p-nitrophenol and degradation of Rhodamine B were studied and compared.First,gold nanobipyramids were prepared by the seed growth method.Thereafter,through the steps of excessive growth of silver ions,CTAB induced precipitation and silver shell etching,the gold nanobipyramides with many shapes were successfully purified to provide a uniform and high-yield gold nanobipyramid.Then,bimetallic core-shell structure of gold nanobipyramid@copper（AuNBP@Cu）was obtained by using PAA as capping agent and hydrazine hydrate as reducing agent.This synthesis strategy is also generally applicable to other gold nanoparticles@copper core-shell structures.Finally,the catalytic activity of AuNRs,AuNBP,AuNR@Cu,AuNBP@Cu and pure Cu NPs was compared.The degradation of rhodamine B by gold-copper bimetallic nanoparticles is about 5 times that of pure gold/copper nanoparticles.For p-nitrophenol,the catalytic efficiency of gold-copper bimetallic nanoparticles is 3.15 times that of pure copper nanoparticles.It was confirmed that the synergy between gold and copper nanoparticles was effectively improved in the catalytic reduction of p-nitrophenol and the degradation of rhodamine B.3.The spherical and flake silver nanoparticles were respectively prepared by surfactant assisted seed growth method and studied their catalytic activity in the catalytic reduction of p-nitrophenol.This part of the work studied the control of silver nanoparticle morphology by the reaction conditions such as the amount of silver seed solution added,the concentration of surfactant.The catalytic activity of these silver nanoparticles with different morphologies on 4-nitrophenol was studied to verify the effects of catalyst dosage and catalyst morphology on the catalysis reaction.The phenomena such as reaction induction period and catalyst poisoning were also found.After calculation,the apparent catalytic activity of the unit catalyst of the flaky silver nanoparticles is 7.1×10³ s^-1/mol Ag and 8.0×10³ s^-1/mol Ag（in terms of Ag atoms）.This work is of great significance for the basic preparation operation of metal nanocatalysts and further understanding of catalysis,so it has been designed as a professional experiment for undergraduates and applied in practice.In summary,the work in this paper mainly studied the preparation of monometallic and bimetallic nanoparticles of gold,silver and copper,and their corresponding catalytic properties,the synergistic effect between bimetallic nanoparticles was found and verified,which may be beneficial to stimulate the potential of active component in catalysts and may have significance in the future catalytic research.