Abstract
The synthesis of both nanosized palladium-silver and silver colloids by chemical reduction using formaldehyde was investigated in this thesis. The effect of polyvinylpyrrolidone (PVP) on the precipitation mechanism was specifically studied. It was found that due to the strong interaction between Pd ions and PVP molecules, the Pd content in the co-precipitated products would be less than corresponding ones obtained in the absence of PVP molecules. This method could produce palladium-silver alloy colloids of 2~3 nm with a Pd rich core. Increasing PVP quantity would increase the palladium-silver alloy particles, and also make the size distribution much broader.Polyvinyl pyrrolidone (PVP) of three different molecular weights (MW = 8,000, 29,000, 55,000) were studied in this thesis on their ability to stabilize silver colloids. Our results indicated that their effects against agglomeration would depend to a great extent on the alkaline used for the promotion of reduction reaction at ambient temperature. When NaOH was used, the reaction rate was very fast and hence only PVP with large molecular weight could produce silver colloids of sizes around 20 nm. On the other hand, when Na2CO3 was used, the reaction path was significantly changed and slowed down as well. Under this circumstance, PVP with MW of 8,000 offered the best protection against agglomeration. It could produce silver colloids of only 5 nm and the size distribution was nearly uni-modal. Increasing PVP quantity had only slight effect on silver size. In addition, the sintering behavior was also briefly studied for these nanosized palladium-silver alloy and silver colloids.