Noble Metal Nanoparticles Monolayer Self-Assembly And Optical Properties

Due to the unique surface plasma effect,noble metal nanoparticles are widely used in optical imaging,photocatalysis,photothermal sensing and surface enhanced Raman scattering(SERS).The metal nanoparticles assembled on the surface of the carrier not only have the optical properties of the precious metal nanoparticles themselves,but also exhibit unique photoelectric properties due to the synergistic effect between the precious metal nanoparticles and the carrier surface.Therefore,seeking a simple and effective assembly method to realize self-assembly of metal nanoparticles is crucial for studying the optical properties of nanoparticle.Based on this,this thesis mainly focuses on the self-assembly and optical properties of dense monolayers of various metal nanoparticles.The specific contents are as follows:(1)Isotropic gold nanospheres and anisotropic gold nano-bipyramid were prepared by seed growth method.The Au@Ag nanorods were prepared by epitaxial overgrowth method using the successfully prepared gold nano-bipyramid as the core.Sea urchin-like tungsten oxide nanoparticles were prepared by solvothermal method.The prepared nanoparticles were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and UV-Vis absorption spectroscopy.The results show that the isotropic gold nanospheres and the anisotropic gold nano-bipyramid have uniform size,regular morphology and good dispersion;The size of the prepared Au@Ag nanorods can be controlled by adjusting the ratio of Au/Ag.With the increase of the size of the nanorods,the location of the absorption peak is also red shifted;Sea urchin-like tungsten oxide nanoparticles with large surface area and abundant tips are good templates for constructing three-dimensional SERS substrates.(2)Based on the self-healing properties of liquid-liquid interface self-assembly and the advantages of Marangoni effect self-driven compression,a three-phase oil/water/oil(O/W/O)system was designed for the preparation of large-area and highly repeatable monolayers of nanoparticles.The tension gradient between different oil-water interfaces makes it easy for nanoparticles to spontaneously transfer from the lower O/W interface to the upper O/W interface and form a dense monolayer.Compared with the previous two-phase interface self-assembly strategy,this three-phase system can be applied to a series of oil solvents without specific restrictions.the monolayers prepared by the three-phase interface self-assembly method have good uniformity and reproductivity at different concentrations of nanoparticles.Finally,the experimental results show that the three-phase interface self-assembly method is suitable for the assembly of nanoparticles with different sizes,shapes,components and surface ligands,which provides a useful exploration for the development of multifunctional nano-devices.(3)The composite three-dimensional SERS substrate was prepared by attaching a monolayer of Au@Ag nanorods on the surface of sea urchin-like tungsten oxide nanoparticles.Due to the large specific surface area and special tip morphology of sea urchin-like tungsten oxide nanoparticles,the high-density spatial hot spot distribution was formed after they were combined with the Au@Ag nanorods,which would greatly improve the SERS activity of the substrate.In addition,the SERS performance of the composite matrix was optimized by adjusting the length of the Au@Ag nanorods on the substrate surface.The results showed that the combination of the Au@Ag nanorods with the composite size of 120 nm of tungsten oxide had the highest SERS activity,and the enhancement factor was as high as 1.7×10~9.Thanks to the effective interface self-assembly method,the prepared 3D SERS substrate showed excellent repeatability,and the relative standard deviation of signal strength was reduced to 6.73%.