The Synthesis, Characterization, And Optical Property Of Core-Shell Structured Noble Metal Nanomaterials

Core-shell structured noble metal nanocomposites processes high stability, excellently catalytic and optical properties. Hence, developing simple and large-scale process for the preparation of these composite materials is very important for their further application. Recently studies showed that taking advantage of multi-functional characteristics of the reagent could simplify the synthesis of nano-structured materials. In our work, we have developed simple methods for the preparation of core-shell structured noble metal nanocomposites by taking advantage of multi-functional characteristics of the reagent.(1) Alkanethiolate-stabilized metal NPs has received intensively contemporary interest for that they are highly stable and can be easily isolated as stable solids, redissolved without irreversible aggregation and easily handled as molecular solids. In previous reports, the preparation procedure is complex and a mass of toxic organic solvent and expensive phase-transferred reagent were necessary. Thus, developing an effective strategy to prepare stable Ag NPs with controllable size in a broad range is an ongoing challenge. We have developed a simple"a step"process to prepare thiol-stabilized metal Ag nanoparticles by using the multi-functional characteristics of the dodecanethiol. Furthermore, the Ag phase could transform into the Ag₂S phase by prolonging reaction time or increasing reaction temperture. By using XRD, IR and TEM, the possible formation and size evolution mechanism of Ag NPs was proposed. This method provides an promising strategy for the preparation of stable Ag NPs due to its simple one-step operation, easy large-scale production and size control and no need of the toxic organic solvent.(2) The core colloids modified with metal nanoparticles possess excellent optical, electric and catalytic properties. For example, assembling metal NPs onto the surface of the supports allows them to retain high activity on cycling, enhance their pH and temperature stability, and enable easy separation from the reaction medium by centrifugation for reuse. Many methods were developed for depositing metal NPs on core colloids. A common feature of all these approaches is that the reductant (and/or metal ions) and the core colloids are separated before the formation of the metal NPs-core colloid composites. This may lead to complex operation processes, presence of residual metal NPs and reductant in the system or lower yield of composite colloids. In our work, by using PEI as both a linker and an"in situ"reductant, we have developed a simple method to prepare Ag-PS composites. The method is based on the formation of a composites composed of core colloids (PS spheres), reductant (PEI) and metal ions. Heating treatment can transform the composites into Ag-PS colloids. Later, the method was further improved and extended as a general strategy to deposit Au (Ag) NPs onto various core colloids, including inorganic spheres (SiO₂), organic polymer colloids (PS) and semiconductor oxide (ZnO). The method is promising synthetic strategy for the preparation of core colloids modified with metal NPs due to its simple operation, easy larger-scale production and generality for various core colloids. Furthermore, based on the results obtained from the method, an improved"surface seeding and shell growth"technique was used to prepare core colloids with thick metal coverage. The metal coverage was easily tuned by changing the initial mass ratio of metal ions to core colloids. Accordingly, optical plasmon resonance of the composites could be tuned in a broader spectrum range by changing the metal coverage.