The Nanofabrication Of Gold-platinum Composite Nanostructures And Their Light-scattering Imaging Analysis At Single Nanoparticle Level

Metal composite nanostructures refer to the integration of two or more metal elements in a nanostructure.Due to their atomic arrangements,crystal structures,crystal faces,and composition,various nanostructures can be formed,including alloys,core-shell structures,core-frame structures,heterostructures and so on.Compared with metal nanostructures with single element,metal composite nanostructures have higher catalytic activity,excellent optical properties,better selectivity and sensitivity,and better stability and other advantages.Therefore,metal composite nanostructures have rapidly developed in the fields of nano-optical devices,catalysis,biological probes,biochemical sensing,drug loading,photothermal therapy and enhanced spectroscopy?fluorescence,Raman,infrared?.At present,it has developed a lot of methods for forming metal composite nanostructures with some disadvantages,such as complicated process,large amounts of reducing agents,and long time-consuming.Currently,researchers pay more attention to the controllable formation of metal nanocomposites with specific structures,morphologies,sizes and properties,but they are scarce in obtaining structural and optical evolution information during the formation process.Moreover,the photo-electron effect and photothermal effect from Localized surface plasmonic resonance?LSPR?of noble metal nanoparticles can be used to enhance the photocatalytic reaction.However,the ultra-short lifetime of hot carriers has severely hindered the development of its imaging technology and the mechanism of plasmon enhanced photocatalysis,and greatly limited the practical application of metal composite nanostructures.In view of the above-mentioned problems and difficulties of metal composite nanostructures,this thesis mainly focused on the formation process of Au-Pt composite nanostructures and their light scattering imaging.The main points of our work are summarized as follows:1.Formation of hollowed-out Au@Ag Pt core framework nanostructures and their light scattering imaging at single-particle level.Nanofabrications such as sculpting hollow and porous plasmonic-metal nanocrystals have received tremendous interest since these kinds of nanostructures with hollow interiors and solid shells usually have remarkable properties.Firstly,Au@Ag core-shell nanocubes?Au@Ag CSNs?are prepared and used as sacrificial templates.Since the standard reduction potential of Pt Cl₆^2-/Pt?0.74 V vs.standard hydrogen electrode,SHE?is much higher than that of Ag Cl/Ag?0.22 V vs.SHE?,the spontaneous replacement of four Ag atoms by depositing a Pt atom occurred via galvanic replacement?GR?reaction.Owing to the different activity of the{100}and{110}facets of Au@Ag CSNs in a medium of Cl^-that is originated from the capping agent of cetyltrimethylammonium chloride?CTAC?,the dissolution of Ag atoms from{100}was in general faster than the deposition of Pt atoms on the{110}facets,so the well-defined hollowed-out Au@Ag Pt core-frame nanostructures?Au@Ag Pt CFNs?were formed.Combined with electron microscopy and dark-field light scattering imaging?DFM?,the evolution of structural morphology and scattering properties from Au@Ag CSNs to Au@Ag Pt CFNs was explored.During the evolution of morphological transformation from Au@Ag CSNs to Au@Ag Pt CFNs,the optical properties and reaction kinetics could be effectively monitored by real-time and in situ plasmonic scattering imaging at single nanoparticle level and surface-enhanced Raman scattering spectra.Moreover,finite difference time-domain?FDTD?method was employed to simulate the scattering signals of an individual particle by LSPR during the GR reaction.The as-carved Au@Ag Pt CFNs has promising plasmon-enhanced electrocatalytic activity,far surpassing those such as Ag-Pt nanocubes.Monitoring the formation process of nanostructures through single particle light scattering imaging is expected to become an effective research method for the study of reaction mechanisms.2.Imaging of hot electrons transfer across Au-Pt porous Interface.Plasmonic photocatalysis on bimetallic heterostructures via hot electrons has received significant attention owing to their ability to harvest solar energy and high catalytic activities,whereas the mechanism of hot electrons transfer at the metal-metal interfaces is still not completely understood.The hot electrons from LSPR of noble metal nanostructures can be used to drive and enhance the photocatalytic reaction.Herein,we at first directly image the hot electrons transfer at metal interfaces by DFM,and then discuss the transfer distance of hot electrons.Firstly,gold nanospheres?Au NSs?of about 47 nm with excellent LSPR characteristics were selected.Owing to the generation of hot electrons in Au NS under the plasmonic resonance illumination,the closely adsorptive Pt Cl₆^2-on the Au NS surface was reduced to Pt?0?atoms,and then Pt?0?atoms deposited on the surface of Au NS to form an Au@Pt porous core-shell nanostructure?Au@Pt NS?,which have enhanced PRLS intensity with a red shift of characteristic resonance frequency as compared to Au NS,making that the process of hot electrons transfer was effectively real-space and real-time imaged.Combined in situ PRLS imaging and scanning electron microscopy?SEM?,hot electrons transfer from a single Au NS as the reaction progressed could be quantified.Furthermore,it has confirmed that the hot electrons donor,the hot electrons acceptor,PRI,and the hole scavenger are very critical to the hot electrons transfer at the Au-Pt interface.Noteworthily,hot electrons can transfer longer than 20 nm at porous Au-Pt interface to mediate the photocatalytic reaction,with the aids of ultrafast transient absorption spectra and transient photocurrent responses.The studies make that the hot electrons could be effectively real-space and real-time imaged and promote understanding the distance of hot electrons transfer at metal interfaces for improving efficiency in hot-carrier extraction science.3.Formation of Au@Pt core-shell nanostructures by hot electrons printing and its application in peroxide measurement.The hot electrons from LSPR of noble metal nanostructures can be used to drive and enhance the photocatalytic reaction.In this study,three types of gold nanoparticles?Au NPs?with different morphologies were prepared,namely,gold nanospheres?Au NSs?,gold nanorods?Au NRs?and gold nanobipyramids?Au NBPs?.Owing to the generation of hot electrons in Au NS under the plasmonic resonance illumination,the closely adsorptive Pt Cl₆^2-on the Au NS surface was reduced to Pt?0?atoms,therefore,the nanobrush of hot electrons painted Pt atoms on the surface of the original Au NPs to form Au@Pt porous core-shell nanostructures?Au@Pt NPs?.Based on this principle,an appropriate amount of Au NPs was modified on the ITO,and the Pt layer was further brushed by nanobrush of hot electrons to prepare three Au@Pt NPs/ITO electrodes with different morphologies.Combined with electron microscopy and DFM,the evolution of structural morphology and scattering properties of Au@Pt NPs/ITO was explored.The electrochemical redox reaction of H₂O₂ at the modified electrode interface was investigated,and it was found that all three Au@Pt NPs/ITO electrodes performed to promote the electrochemical redox reaction of H₂O₂ at the modified electrode interface and increase the electrochemical redox peak current of H₂O₂.Furthermore,the reaction kinetics of H₂O₂ at the electrode interface was investigated.Finally,based on the high electrocatalytic activity of Au@Pt NRs,an analytical platform for detecting H₂O₂ was constructed.A new method was used to synthesize metal composite nanostructures with excellent catalytic performance,which provides an alternative approach to design metallic nanoarchitectures with complex structures and precisely tailored properties with excellent performance.In conclusion,we focused on the formation of Au-Pt composite nanostructures and their light scattering imaging,and proposed a method for forming Au-Pt composite nanostructures based on strategies crystal faces selectivity and hot electrons-driven reduction.The evolution of structural morphology and scattering properties of Au-Pt metal composite nanostructures and the transfer of hot electrons at the Au-Pt interface were imaged.Finally,the electrocatalytic properties of Au-Pt composite nanostructures are explored and applied to the measurement of HER and peroxide.This research offers new insights for the formation of metal composite nanostructures,light scattering imaging,and biochemical analysis.