Controllable Preparation And Application Of Gold Nanoflowers@Silver Core-shell Nanomaterials

Noble metal nanocomposites have attracted much attention in material science duringthe past decades for their unique optical, electrical, magnetic and catalytic properties.Noble metal nanocomposites not only possess the properties of each component butalso canresult innovel properties or functions. To data, noble metal nanocompositeshave already shown great potential in biomedicine, industry catalysis, chemicalanalysis and clinical diagnosis.In order to develop more facile and efficient methodsfor the preparation of noble metal nanocomposites, this report focused on thecontrollable preparation of gold nanoflowers (NFs)@silver core-shell nanocomposites.A series of nanocomposites with different morphology were prepared. We furtherinvestigated the properties of the nanocomposites and their application in catalyst andsurface-enhanced Raman spectra（SERS）. The results are summarized as follows:1） AuNFs@Agcore-shell nanocomposites were prepared through seed-mediatedgrowthstrategy by using55nm Au nanoflowers was as seeds, sodium citrate asstabilizer, ascorbic acid as reducing agent and silver nitrate as metal precursor.We systematically investigated the influence of pH on the synthesis andproperties of AuNFs@Ag core-shell nanomaterials since that solution pH havesignificantly impact on the coordination of sodium citrate with Au as well as thereducing activity of ascorbic acid. It was found that the pH played an important role in the morphology and stability of the AuNFs@Ag core-shellnanocomposites. The as-prepared material under optimal conditions (pH5.5-10.0)had excellent stability against salt （40mM NaCl）and temperature (70℃).2） The SERS and catalytic activity of the AuNFs@Ag core-shell nanocompositeswas further studies. We showed that the nanocomposites were superior to singlegold nanoflower without silver shell for enhancing the Raman signal ofRodamine6G due to the high coverage of Ag shell and the strong anisotropy. Thenanocompositesprepared at pH7.1showed the best performance for SERS.Moreover AuNFs@Ag core-shell nanomaterials can be used for catalysis of thesodium borohydridereduction of4-nitroaniline.The nanomaterialsprepared underacidic pH condition showed the best catalytic activity.