Abstract
Nanosize material technology have attracted much attention in recent years due to their special chemical and physical properties. In the study, we used chemical reduction method to prepare nanosize Pd, Ag, and Pd-Ag particles in aqueous solution. Formaldehyde was used as reducing agent, NaOH and Na2CO3 were used as precipitation agents, and PVA(poly vinyl alcohol) or PVP(poly vinyl pyrrolidone) were used as protective agents. In regards of processing condition, a well dispersed, 10nm size silver particles can be prepared under the condition of PVA/AgNO3=6.2~10.34, HCHO/AgNO3=4, NaOH/AgNO3=1, and Na2CO3/AgNO3=1. Since PVP was used as a protective agent, a well dispersed, high yield(>99%), 10nm size silver colloids can also be prepared under the condition of PVP/AgNO3=2.25~9.01，HCHO/AgNO3=4~100，NaOH/AgNO3=1，and Na2CO3/AgNO3=1.In our work, PVP shows a better protective effect than PVA. The silver colloids solution, after diluting with five times volume acetone, can be separated by centifugation, and redispersed later on. In regards of reaction mechanism, the formation of silver colloids was an instant reaction. Silver atoms exchange and colloids aggreation processed in the following reaction times.On the other hand, the formation of palladium colloids was an autocatalytic reaction with an induction period. The protective agent of PVP behaves as a weak acid with a value of Ka=1.3x10-5.In the preparation of Pd-Ag colloids, silver precipitated first to form nuclei, accompanied by Pd coprecipitation to form Pd-Ag bimetallic colloids.