Preparation, Separation And Properties Research Of Noble Metal Nanoparticles

Noble metal nanomaterials have achieved a wide variety ofapplications in areas such as catalysis, sensing, optoelectronic device,biomedicine and surface-enhanced Raman scattering (SERS). Theirunique physical and chemical properties are determined by a set ofparameters including size, shape, composition, and structure (e.g., solidor hollow). Thus, obtaining monodisperse nanocrystals and investigatingformation mechanism of nanomaterials is of great significantance fortheir performance and application. Herein, we focused on studying howto gain monodisperse silver and palladium nanoplates, analyze reactionprocess between triangular Ag nanoplates and HAuCl4, and investigatecatalytic activity of platinum nanoparticles. Details are listed as followes:1, Ag nanoplates were synthesized by chemical solution reductionmethods with different reducing reagents including sodium borohydride(NaBH4), N,N-dimethylformamide (DMF), Hydrazine hydrate(N2H4·H2O) and poly(vinylpyrrolidone)(PVP). Among them, triangularAg nanoplates obtained by NaBH4reduction method had a gooddispersivity and their size laid between45-85nm. The morphologies of products were all plate-like without other shapes. Density gradientcentrifugation separation was introduced to narrow the size distribution ofAg nanoplates. The effective separation of Ag nanoplates according totheir size was achieved with20%-60%of ethylene glycol (EG)/H2Osolution as gradient medium. UV–vis absorption spectra and TEM of thefractions indicated that Ag nanoplate has surface plasmon resonance (SPR)absorption peak which is extremely sensitive to change in size and thein-plane dipole SPR band of Ag nanoplate is red-shifted as edge sizeincreases.2, Density gradient centrifugation (DGC) separation method wasemployed as a process-analysis microsystem by introducing a reactionzone, which allows intermediates to be captured after reactions for tens ofseconds. As a paradigm, we chose the galvanic replacement reactionbetween Ag nanoplates and HAuCl4as a typical model to evaluate themicrosystem. Combining the extended DGC method with localcomposition analysis, direct evidence has been obtained showing that thegalvanic replacement reaction starts from both the edges and at somepoints on plate surface at a relatively high AuCl-4concentration.3, Hexagonal and triangular Pd nanoplates were prepared through thereduction of Na2PdCl4by PVP in the solution-phase. The molecularweight and concentration of PVP and the existance of Br-aftected themorphology of nanoparticles. We tried to separate Pd nanoplates according to their shape and size differences by DGC separation withethylene glycol (EG)/H2O solution as gradient medium.4, The Pt/C and Pt/C-N catalysts were prepared via the reduction ofchloroplatinic acid by sodium borohydride, using the carbonaceousmaterials and N-doped carbonaceous materials prepared by hydrothermalmethods as the supports, respectively. The size distribution of Ptnanoparticles loading on the N-doped carbonaceous materials wasnarrower than Pt/C catalyst. The catalytic activity of Pt/C-N wassignificantly higher than that of Pt/C catalyst in P-nitrophenol reductionreaction. The conversion obtained with Pt/NC reached to95%after about0.5h. The results showed that the size and dispersion of Pt nanoparticlesdirectly influenced the catalytic performance.