Preparation And SERS Properties Of One-dimensional And Core-shell Structural Silver Nanomaterials

The surface-enhanced Raman scattering (SERS) technique is a powerful analyticaltechnology that is able to provide rich structural information in a nondestructive manner forvarious analytes, including single organic molecules. The key to achieve excellent SERSproperty is the fabrication of a suitable substrate. The aim of this research is focused on thedesign and synthesis of various one-dimensional and core/shell Ag nanomaterials as SERSsubstrates with high SERS sensitivity/activates.(1) Ag nanowires with a high aspect ratio were successfully synthesized at the presenceof polyvinylpyrrolidone (PVP) through the polyalcohol method. A comparative researchcontaining eight different reaction parameters combinations was performed by the method oforthogonal test, so as to obtain the optimal synthesis condition of Ag nanowires growth. Themorphologies and structures of Ag nanowires were investigated by various techniques of highresolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM),X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fouriertransform infrared spectroscopy (FTIR). The results showed that the optimal experientialparameters for obtaining the highest aspect ratio of Ag nanowires could be realized at thefollowing conditions: the molar ratio of PVP: AgNO3is4:1, PVP and AgNO3were droppedinto the reaction solutions at the same time, and no addition of the reagents of NaCl, FeCl3,H2PtCl6. A simple and cost-effective approach was introduced to assemble Ag nanowires SERS substrate with high density “hot spots” created by nanowires junctions. Theenhancement factor (EF) is estimated to be of about4×106.(2) SiO2/Ag core-shell nanospheres (CSNS) were prepared by a novel two-step methodat the aid of the reduction and immobilization function of high density coverage of thiolgroups on the surface of mercapto-silica spheres. Firstly,3-mercaptopropyl trimethoxysilane(MPS) was hydrolyzed in ammonia solution by the St ber method to form uniform spheres.Secondly,[Ag(NH3)2]+ions were mixed with MPS micro-spheres in sodium hydroxide(NaOH) aqueous solution using glucose as reluctant to obtain SiO2/Ag CSNS. Any additionalmodification agent was not needed in this process. The Ag Nanoparticles (NPs) were robustlyadsorbed on the surface of MPS micro-spheres through the thiol function groups. The size andcoverage density of Ag NPs on the MPS spheres could be conventionally tuned by adjustingthe concentration of the [Ag(NH3)2]+ions. Raman test results show that the as-prepared AgNPs coating MPS core-shell structures have a potential as SRER substrates due to itsintensive “hot spots” distribution by using4-mercaptophenol (4-MPh) as an analyte.(3) Cu2O/Ag core-shell hybrid nanocubes were successfully prepared at the presence ofglucose by a novel strategy. The morphologies and structures of Cu2O/Ag nanocubes werecharacterized by various techniques of TEM, SEM and XRD. The reaction temperature has asignificant effect on the final morphology of Cu2O/Ag core-shell hybrid nanocubes and theload density of Ag on the Cu2O. Raman spectrometer measurement showed that these novelCu2O/Ag hierarchical heterostructures exhibited fascinating Raman enhancement property forthe4-MPh probe molecules. (4) A rapid growth method to synthesize Ag/Al2O3core/shell nanodendrites (NDs)crystals on Al foil through an electroless galvanic displacement reaction between aluminumfoil and [Ag(NH3)2]+ion was presented. The result showed that the as-synthesized surfacemodified Ag nanodendrites exhibited a face centered cubic crystalline structure. The presenceof a uniform thin film of Al2O3, depositing on the surface of Ag NDs can prevents its possibleoxidation and help maintaining the dendrites shape. This synthesis method is facile andenvironmental friendly without using any reducing or capping agents. Raman test showed thatthese nanocomposite exhibited excellent SERS performance.