Preparation And Application Of Organic-nobel Metal Hybrid Nanomaterials

Metal nanoparticles have been extensively applied in many fields because of theirunique quantumconfinement effect, size effect and surface effect. These basic propertieslead to special optical properties-surface plasmon resonance (SPR), which was determinedby their size, shape, composition, crystalline and assemble structures. Therebysize-controlled and morphology-controlled preparation of nanomaterials is very important.The application of metallic nanoparticles in surface-enhanced Raman scattering (SERS),surface-enhanced fluorescence (SEF) and catalytic property have been a hot topics innanoscience and nanotechnology. Interactions between the plasmons of noble metalnanocrystals and organic molecules have recently received enormous interests and willlead to a wide range of chemical sensing applications. In this dissertation, solution-basedchemical methods have been developed to synthesize metallic nanoparticles, i.e., Au-Agalloy, Au bipyramids (AuBPs) and Au-Ag-Pd trimetallic nanoparticles. Then, theinteraction betweene the fluorescence molecule and metal NPs and the surface-enhancedfluorescence were discussed. Furthermore, the Au-Ag-Pd ternary metal composite NPshave been prepared and characterized thoroughly, which showed a remarkable catalyticproperty compared to AuBPs. Finally, hydrophobic naonofibers were prepared byabsorbing highly puried AuBPs on the surface of electrospun PAN nanofibers, which canbe used as SERS-active substrates for high sensitivity detection of low concentration ofanalyte molecules. The main work of this paper dissertation is summarized as follows.1. Au-Ag alloy nanoparticles have been synthesized in aqueous medium using acitrate reduction method. UV-vis spectra, STEM-EDS and HRTEM confirm the formationof alloy nanstructure. A nanometer-thin silica spacer layer was employed to separate themolecules away from the metal surface to avoid fluorescence quenching. Squenently, afacile and rapid approach for detecting low concentration of iron ion (Fe3+) with improvedsensitivity was developed on the basis of plasmon enhanced fluorescence and subsequentlyamplified fluorescence quenching. Au1Ag4@SiO2nanoparticles were dispersed intofluorescein isothiocyanate (FITC) solution. The fluorescence intensity of the FITC solutionwas improved due to plasmon enhanced fluorescence. However, efficient fluorescence quenching of the FITC/Au1Ag4@SiO2solution was subsequently achieved when Fe3+witha concentration ranging from17nM to3.4M was added into the FITC/Au1Ag4@SiO2solution, whereas almost no fluorescence quenching was observed for pure FITC solutionunder the same condition. FITC/Au1Ag4@SiO2solution shows a better sensitivity fordetecting low concentration of Fe3+compared to pure FITC solution. The quantized limit ofdetection (LOD) toward Fe3+was improved from4.6M for pure FITC solution to20nMfor FITC/Au1Ag4@SiO2solution.2. A seed-mediated method has been used to grow Au bipyramids in aqueous solutionsusing cetyltributylammonium bromide (CTBAB) surfactants as stabilizing agents in thepresence of AgNO3. The yield of Au bipyramids was abount30-50%due to the presence ofbyproducts gold nanospheres. We developed a relatively facile and highly efficient methodfor shape-selective separation of AuBPs from impurities by tuning the surfactantconcentration of cetyltrimethylammonium bromide (CTAB) to create an entropic,short-ranged depletion attraction between AuBPs. After purification, the purity is over95%.3. Heterogeneous nanostructures made of highly purified AuBPs were prepared. Themultiply twinned nanostructure of AuBPs results in a totally different second-metal growthmode. Silver exhibits highly preferential growth at the ends of the multiply twinned AuBPs,giving rise to bimetallic nanorods. On the basis of AuBPs@Ag NPs, Site-specific growthof AgPd nanodendrites on AuBPs from core-shell to tipped-AuBPs nanostructure wasachieved for the first time by innovatively coupling galvanic replacement withco-reduction process. AuBPs@AgPd nanodendrites nanostructures show remarkablecatalytic activity in the reduction reaction of4-nitophenol (4-NP) by NaBH4.4. Electrospun polyacrylonitrile (PAN) nanofibers modified by sulfhydryl moleculesabsorbed a lot of AuBPs through Au-S bond, which showed hydrophobic property andSERS activity. Since the synergistic effect of the local field enhancement of AuBPs and thehydrophobic surface, the Raman spectra of hydrophobic PAN/AuBPs nanofibers showedan apparent enhancement in the signal of rhodamine6G (R6G) molecules dropwised onthe PAN/AuBPs nanofibers. When the concentration of rhodamine6G is10-10M, theRaman signal can still be detected.