Surface-Enhanced Raman Spectroscopy Used In Molecular Orientation And Ligand Exchange Reactions On Gold Nanoparticles

The surface of gold nanoparticles is usually covered with a layer of protective ligands. It is one of the hotspots in the field of nanomaterials to know about the ligand because the surface properties of the gold materials are directly affected by the ligand molecules. In recent years, solid state NMR, sum frequency generation (SFG), surface-enhanced Raman spectroscopy (SERS) are applied to characterize the surface ligand molecules.Molecule signals can be enhanced by Surface-enhanced Raman scattering (surface-enhanced Raman scattering, SERS) for about one billion times, so that SERS can be used to detect the monolayer molecules. In addition, the SERS is vertical selectively so that the signal of vibration mode perpendicular to the substrate can be greatly enhanced. That made it can be used to detect the orientation of adsorbed molecules on the surface, which greatly enriched our understanding of molecules on the surface.In this thesis, SERS was used to detect the surface ligand and was applied in ligand exchange reaction; based on the perpendicular selective enhancement mechanism of SERS, molecular orientation on different size nanoparticles was studied in this paper. In this paper, experimental design, experimental implementation, results and other aspects of characterization were carried out as follows:1:SERS was used to analyze the molecular orientation on the surface of different diameter gold nanoparticles. The citrate-protected 16nm and 70nm gold nanoparticles was fixed on a flat substrate by self-assembly, then diphenyl disulfide was adsorbed, the orientation difference of benzene ring on different size nanoparticles was gotten by comparing the difference of SERS signal from different particle size:the benzene ring was tend to parallel to the gold nanoparticles on smaller nanoparticles; Diphenyl disulfide protected 3nm gold nanoparticles was synthesized, then two kinds of SERS substrate (silver mirror reaction and etched silver foil) was used to detect the surface ligand molecules and their molecular orientation.2:Characterization of ligand exchange reactions by SERS. Three kinds of ligand exchange reactions was carried out as following:(1) diphenyl disulfide was used to replace oleylamine on the surface of 15nm gold nanoparticles; (2) diphenyl disulfide was used to replace pentanethiol on 3nm gold nanoparticles, and then Infrared spectroscopy to detect the ligand exchange reactions; (3) diphenyl disulfide was used to replace Octadecanethiol on 3nm/15nm gold nanoparticle surface. The results showed that benzene disulfide can replace Octadecanethiol on 3nm gold surface, but can not replace it on 15nm gold surface. This is probably due to the orientation difference of diphenyl disulfide on the different radius gold nanoparticles, which causes differences in reactions.