Synthesis Of Anisotropic Noble Metal Nanoparticles And Investigations On The Shape Transformations Through In Situ Liquid Cell TEM

Noble metal nanoparticles with controlled morphologies are widely investigated due to their unique optical and structural properties.However,current established protocols of synthesis of noble metal nanoparticles usually are complicated and with high costs.The lack of synthesis of high-yield and monodisperse noble metal nanoparticles is prohibiting their industrial applications,which is an urgent need in this field.In addition,most of the existing studies on the growth mechanism of nanomaterials are based on non-in situ observations.The in situ electron microscopy technique allows real-time observation of the chemical reactions of nanoparticles.This method can provide a deeper understanding of the behavior of nanoparticles.If in situ electron microscopy can be used to observe the chemical reaction behavior of nanoparticles in real time,it will play an irreplaceable role in the study of the growth mechanism of nanomaterials.In this dissertation,gold nanorods and nanotriangles with uniform morphologies and high yields were synthesized by rapid and simple methods,and their growth mechanisms were further investigated by careful characterizations and discussions.By synthesizing homogeneous noble metal composite nanomaterials and applying them in the field of electrocatalysis,better catalytic performance on methonal oxidation reaction of the catalyst was obtained.The morphology transformation process of core-shell nanostructure was observed by in situ liquid cell electron microscopy and the mechanism was carefully discussed.The work of this dissertation includes the following sections:1.Monodisperse AuNRs can be obtained through seed-mediated growth method within 15 min after seed injection,which is much faster than existing protocols that take several hours.It is proved that the most critical factor in the seeded growth of gold nanorods(AuNRs)is the complex,CTA-Br-Ag+,which can selectively bind onto certain facets of Au seeds and facilitate the formation of anisotropic nanostructures.2.Monodispersed triangular gold nanoplates with tailored edge length and tunable SPR properties have been prepared through a rapid seedless growth process.It is believed that iodide ions can promote the formation of gold nanoplates by both selective binding onto the Au {111} facets and oxidative etching to remove less stable gold nuclei,leaving behind dominant planar structured nuclei.3.A template method was used to synthesize gold nanoplates through the overgrowth of Au/Ag nanorings,in which polyvinylpyrrolidone(PVP)and H2O2 were used as a stabilizer and a reducing agent,respectively.Mechanistic studies show that the overgrowth of Au/Ag nanorings experienced two sequential growth processes along the"inner ring" and "outer ring" directions,respectively.4.High yield PtPb nanoplates were successfully prepared with the presence of DEG.The as-prepared PtPb nanoplates are with uniform alloy structure.In the methanol oxidation reaction(MOR)measurement,the nanoplates possess the highest mass activity of 3,895 mA mg-1Pt which is 6 times than commercial Pt/C.In addition,the PtPb nanoplates also possess the best long-time durability.Through the density function theory(DFT)calculation,we found that the PtPb nanoplates have the strongest tolerance to CO poisoning which may result in their excellent performances in MOR.5.We present in situ graphene liquid cell(GLC)transmission electron microscope(TEM)studies on the dissolution of bimetallic core-shell nanocubes.Using well-defined core-shell nanocubes composed of dissimilar metals,we were able to uncover the anisotropic reaction environment due to the graphene windows.Kinetic analysis after appropriate accounting for extrinsic anisotropy reveals that etching transitions from predominantly edge-selective to layer-by-layer removal of Au atoms during dissolution of Pd@Au core-shell nanocubes.Furthermore,our real-time GLC TEM imaging reveals reaction pathways toward a library of compositionally and architecturally sophisticated nanostructures including bimetallic multipod,segmental nanorod,nanobox and nanocage accessible from controlled etching of core-shell nanocubes.