Synthesis, Application And Spectroscopy Of Nanoparticles Of Metal And Polymer

The assembly of the nanosized metal nanoparticles with functionalized molecules have received considerable attention and shown extensive application in various fields. It has been demonstrated that the properties of the individual particles can be considerably modified by interactions with the substrate and with other particles. One of the most important properties of the metal nanoparticls in the nanodevices is the charge transfer at the interface between the metal nanoparticls and absorbed functional ized molecules. The effect of the substrates on the interfacial charge transfer of the assembled metal nanoparticls, however, has scarcely been studied. It has been well known that the charge transfer (CT) at the molecules/metal interface has contributions to the Surface-enhanced Raman scattering (SERS) of the molecules absorbed on the metal nanoparticles. Besides providing the spectral information associated the interfacial charge transfer, the SERS spectroscopy in fact has proved to be very useful tool to study the molecule/metal nanoparticle systems, due to its richness of molecular structure information, high sensitivity and surface selectivity. In general, the SERS enhancement can be attributed to electromagnetic (EM) and "chemical" mechanism. The EM mechanism is based on that nanoparticles of coinage metal, such as gold and silver, exhibit surface plasmon resonance (SPR) in the UV-visible region due to the collective oscillations of the free electrons inside the particles. Under the SPR conditions, the electric fields near the metal particles can be greatly amplified. The molecules near the surface of the particles consequently undergo an electric field greater than the incident field. The "chemical" mechanism is related to photon-driven charge transfer process which involves dynamic charge transfer between the energy levels of the molecules and the Fermi levels of the metals. In most of the SERS studies, the CT mechanism is normally inextricably linked with the EM mechanism. Nevertheless, it is possible to relatively amplify the SERS spectral features related to the interfacial charge transfer process of the metal nanoparticls by properly controlling the experimental conditions, because the EM mechanism is dependent to the SPR of the metal nanoparticles.In this thesis, the main research works and the conclusions are listed as follows:[1] Stable and uniform-sized silver colloids have been prepared and assembled intotwo-dimensional assembly on glass substrate. Absorption spectra of the assemblies demonstrate that interaction between silver nanoparticles result in large shifts of dipolar surface plasmon resonance, whereas only slight effect was observed for quadrupolar surface plasmon resonance. It may imply that there are close relation between the enhancement of electric field in nearby particles and dipolar interaction.[2] The monolayer and double layer structure of silver nanoparticles were assembled on a polyvinylpyridine modified glass surface. It has been demonstrated that the positive charge in polyvinylpyridine greatly weakens the charge transfer between p-Aminothiolphenol molecules and metal particles, as revealed by the Surface-enhanced Raman scattering spectroscopy. In addition, it is also demonstrated that the haloid ions co-absorbed on the assembly play an important role in controlling the charge transfer between PATP and silver substrate.[3] Instead of PATP, BDT and MBA were used as the linkers for the assembly of the monolayer and double layer structure of silver nanoparticle on a polyvinylpyridine modified glass surface. It finds that they have the same rules. The coadsorption of haloid ions co-absorbed on the assembly also play more important role in controlling the charge transfer between PATP and silver substrate.[4] Surface property of polystyrene particles was modified with copolymerized polyvinylpyrrolidone, uniform and recyclable iodine catalyst particles were prepared by loading iodine onto the copolymer particles. IR spectral characterization indicates that the polyvinylpyrrolidone was incorporated into the polymer chain of the polystyrene. Loading of iodine molecules was achieved by the interaction between the iodine molecules and pyrrolidone residues, which leads to a significant spectral change of the pyrrolidone group. Using dispersion polymerization method, the monodisperse polystyrene particles were synthesized, which are modified by PVP-g-PS copolymers. Continuely, the particles are modified by iodine, to generate a new catalyst.This type of new catalysts can direct transformation of aldehydes to nitriles in ammonia water.The preparation process of the catalyst is very simple and economic. Most importantly, the catalyst can be recycled and re-utilized.