Regulation And Properties Of Bimetallic Plasmonic Nanostructures Based On Gold Nanobipyramids

Noble metal nanoparticles have attracted much attention due to their localized surface plasmon resonance,which has enabled widespread potential applications of metal nanostructures in the plasmonic sensing and imaging,plasmon-controlled optics,photothermal therapy,photocatalysis and so on.The current available materials are gold,silver and copper,which greatly limit the applications of localized surface plasmon resonance.For example,gold and silver are inactive for catalyzing many chemical reactions.The development of bimetallic nanoparticles based on noble metal nanomaterials can combine surface plasmon resonance with other physical/chemical properties,the preparation and properties of which have always been the hotpot of scientific research.Among noble metal nanomaterials,Au nanobipyramids are of concern due to their homogeneity,thermal stability and superior plasmon resonance performance.Therefore,we prepared the bimetallic nanostructures based on the Au nanobipyramids and studied their plasmonic properties and applications in ion detection,photocatalysis and biological therapy.The main results are as follows:1.A facile method for the preparation of Ag nanostructures through Ag overgrowth on monodisperse Au nanobipyramids has been developed.Structural evolution from bipyramids through rices to rods during the Ag overgrowth process is observed,indicating that Ag atoms are preferentially deposited on the side surfaces of Au nanobipyramids.The geometrical shape and plasmon resonance wavelengths are tailored by varying the Ag precursor amount.The spectral evolution of the supported Ag nanostructures is ascertained by both ensemble and single-particle characterizations,in conjunction with electrodynamic simulations.Systematic measurements of the refractive index sensing characteristics indicate that the Ag nanostructures possess high refractive index sensitivities.The highest FOM value for the Au NBP@Ag nanostructure samples is 6.7 RIU^?1,which is among the highest that have been reported for colloidal plasmonic metal nanoparticles in solutions at the ensemble level.Moreover,the Ag nanostructures exhibit greatly improved chemical stability in comparison with Ag nanoplates with a close ensemble plasmon wavelength.The Ag nanostructures remain unchanged even after 22 days.The superior sensing characteristics of the Ag nanostructures are further demonstrated by the detection of sulfide,with the detection limit of 0.1μM achieved.2.A facile method for the preparation of anisotropic Au/silica and Au/Pd nanostructures through selective silica coating on monodisperse Au nanobipyramids has been developed.Silica coating at the end of Au nanobipyramid is associated with the cetyltrimethylammonium bromide concentration.For both the Au nanobipyramid/end-and side-silica nanostructures,the thickness of the silica shell is tunable as the added amount of tetraethyl orthosilicate.The silica can also be selectively coated on the corners or facets of Au nanocubes,indicating that this method is general for Au nanostructures with different curvatures.The further selective deposition of Pd atoms on the anisotropic Au nanobipyramid/silica nanostructures is realized owing to the block of silica.The superior plasmonic photocatalytic activities of the Au nanobipyramid/Pd nanostructures are further demonstrated by the Suzuki coupling reactions at the room temperature.The highest conversion percentage is above 90%.Moreover,systematic measurements of these three types of Au nanobipyramid/Pd nanostructures indicate that the relative position of Pd atoms and electromagnetic hot spots is of great importance for the plasmonic photocatalysis.The highest catalytic activity of Au NBP/Pd nanostructures is achieved when the Pd nanoparticles located at the ends,where the local electric field enhancement is the largest.3.A Pd-tipping process on Au nanobipyramids with the red plasmon shifts up to⁹00 nm has been developed.The large red shift can be ascribed to the deposition of metals at the tips of Au nanobipyramids,confirmed by electrodynamic simulations.This method is successfully applied on Au nanobipyramids and nanorods with different wavelengths,indicating that the plasmon wavelength of Au nanocrystals can be extended to the entire near-infrared region.Pt-induced metal nanoparticles can also be deposited at the tips of Au nanobipyramids and nanorods,suggesting the generality of this approach.The metal-tipped Au nanobipyramids show high photothermal conversion efficiency（79%）.The excellent photothermal therapy performance is determined with the cell viability to be 19%after the 1064-nm laser illumination at the intensity of 2.74 W cm^?2.This research work will be very helpful for the design of plasmonic bimetallic nanostructures,which will flourish the applications of surface plasmon resonance in sensing,biology and energy areas.