The Controlled Of Large Size Au Nanoparticles Of Palladium SERS Substrates Optimization And Synthesis Of High Concentration Of Ag Nanoparticles Modified With Amphiphilic Molecules

The optical properties of Au nanoparticles(NPs) are dominated by their surface plasmons(SPs), i.e., light-induced oscillations of conduction electrons in them. Because nonspherical, anisotropic Au NPs provide multiple oscillation modes for the electrons, and thus changing shape allows tuning the SPs in a more wide r spectral window than changing size. Although the SPs are dependent on particle's size, they show no apparent size dependency for small particles because only dipole mode can be excited. When the particle's size is increased above 100 nm, the SPs, however, show apparent size dependency because dephasing starts to occur in them. To exploit their size-dependent SP properties, it is highly desirable to synthesize large Au particles. Additionally, to prompt their practical applications, we also need synthesize nanoparticles with high concentrations, i.e., developing techniques for the synthesis of nanoparticles in a large scale. Because colloids are thermodynamically unstable systems, the large particles or the particles with high concentrations often easily aggregate during their growth, making their synthesis failure. Until to now, some methods for the synthesis of large Au particles have been reported, amongst which the so-named seed-mediated growth method is mature. However, most of these reported methods reply on choosing suitable stabilizer or reduce agent to stabilize the growing particles or to tune their size, lacking generality. On the other hand, most of the methods for large scale synthesis of nanoparticles rely on experience, providing no theoretical guidance.With these backgrounds in mind, this thesis tries to understand, through systematical experiments and DLVO calculations, the key factors controlling the synthesis of large Au particles. The achieved understanding can guide not only the synthesis of large Au(and other material) nanoparticles but also the large scale synthesis of nanoparticles. The main contents and results achieved are outlined as below:(1) Controlled synthesis of large Au particles with size in the range of 100-180 nm. Through systematical study on the classic synthesis system(using 45 nm Frens Au particles as seeds and using citrate and hydroxylamine as the stabilizer and reducing agent, respectively), this thesis experimentally and theoretically reveals that controlling the concentration of salt produced to prevent the growing particles from aggregation is key point for the successful synthesis of large Au particles using seed-mediated growth method. This is because the large Au particles usually possess large van der Waals forces, making their critical coagulation concentration very low. This understanding implies that large Au particle can be synthesized by feeding dilute reactant solutions, avoiding the necessary of special stabilizer or reducing agents.(2) Opitimizing borrowed SERS at Pd overlayers using these size-controlled large Au particles. The availability of large Au particles paves the way for their diverse practical applications. To this end, this thesis used large Au particles to optimize the borrowed SERS at Pd overlayers, achieved by constant current depositing of ultrathin, pinhole-free Pd overlayers on these pre-synthesized large Au particles supported on an SERS-inactive glass carbon electrode. The results reveal that the high quality SERS observed on these Pd overlayers are mainly contributed by the long-range electromagnetic fields created by the underneath large Au particlels on which the Pd overlayers were deposited(so that the SERS observed is named borrowed SERS). Moreover, the SERS activity can be further optimized by underneath particle's size and the thickness of the Pd overlayers.(3) Colloidal stabilization theory-guided the synthesis of high concentration Ag colloids. Large-scale synthesis nanoparticles usually requires feeding high concentration reactant solutions, thereby resulting in high concentration salt produced. To enable their free growth, the growing particles, based on the understanding of work(1), should be stable enough during their growth, that is, they should sustain this high concentration salt produced. To this end, this thesis used zwitterion ligand to impart the growing particles hydrophilic repulsive force so that their critical coagulation concentrations are largely improved. The achieved results reveal that 13 nm silver particles with a concentration as hihgh as 1.1 × 10-1 mol/L can be synthesized, and moreover, the presence of Cl-1 inons assist the formation of well dispersed Ag colloids.