Novel strategies for the synthesis of metal nanoparticles and nanostructures

Resumo

Metal nanoparticles embedded in host polymers have gained significant interest in recent years. These materials exhibit unique electrical, optical, or mechanical properties making them valuable for applications in many areas. Also, the embedding of nanoscopic metals in polymer matrices is one of the easiest and most convenient way for nanostructured metal stabilization and handling process. The objectives of this thesis research focus on synthesis of silver nanoparticles and nanostructures within various types of polymer matrices. Article one presents three different methods for the synthesis of silver-agar hybrid materials through in-situ approach. This development substantially simplifies the nanocomposite synthesis by eliminating the need for any additional organic reducing or capping agents, which was previously used to stabilize the produced nanoparticles and to suppress their continuing growth. With appropriate synthetic parameters, one can achieve silver nanoparticles or nanostructures by changing the reaction conditions and modifying the fabrication method. Article two describes a simple technique for the preparation of highly concentrated agar gel networks. The resulted gel networks exhibit greater compactness, smaller size porosity and higher mechanical strength in comparison with conventionally prepared gels or with the low concentrated agar gels prepared hydrothermally. These concentrated agar gels can widen the possible applications of this widely used biocompatible polysaccharide. Article three introduces a novel strategy for the fabrication of silver nanostructures coated with polypyrrole polymer by using a relatively low reduction potential solid silver oxide as a metal precursor. The silver nanosnakes are fabricated in-situ in PPy film through hydrothermal treatment, the pyrrole monomer serving as the reducing agent, and as stabilizer for the silver nanostructure formation and enforcing preferential orientation of the silver snakes within the polymer matrix. The silver nanosnakes structure are obtained by fine-tuning the synthetic parameters such as Ag:Py ratio, time and temperature of synthesis reaction. The resulting Ag@PPy core-shell nanostructures are prepared by a simple one-pot reaction, and the peculiar singe crystal silver nanosnake core is obtained without using any additional capping, stabilizing or assistant agent. In Article 4, the growth mechanism of Ag@PPy nanosnakes is investigated. The effect of different preparative experimental parameters on the formation of the peculiar Ag-PPy core-shell nanostructures is carefully studied. The Ag2O agglomerates coated with PPy film is the initial main product obtained before any hydrothermal treatment. The thermal activation of this composite mixture through the hydrothermal treatment cause the formation of silver-PPy agglomerates, which in turn evolve with time to give Ag-PPy core-shell nanostructures as the main product. The presence of the PPy matrix plays a key role in the formation of the single crystal silver nanosnake core. The mobility of the metallic silver produced is limited by the surrounding PPy matrix. This limited mobility slows down the fusing process of the silver aggregated particles together and give them the opportunity to orient themselves due to the assembly process and to produce the peculiar silver-PPy core-shell nanosnakes through oriented attachment growth mechanism. In article five, growth constrains are imposed by an interfacial reaction rather than a polymer matrix. The synthesis and self-assembly of monodispersed Ag nanoparticles is accomplished by a hydrothermal two-compartment set up. This novel stategy yields a golden colored, 2-D array of naked and monodispersed silver nanoparticles formed on the aqueous solution surface without the aid of any additional surface modifying agents to stabilize the nanoparticles or to direct their self-assembly.