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Gold, silver and other precious metals nanoparticles possess unique optical, electrical and catalytic properties , and good biocompatibility, makes its detection , catalysis, bio-sensing , medical imaging and treatment , and other fields are of great application value. And with a two-component composite nanoparticles of gold and silver because of their different from the single- metal nanoparticles optical, electrical and catalytic properties of , causing researchers' attention. This paper in the water phase synthesis, the use of seed crystal growth method , a mixture of ascorbic acid and silver nitrate solution as a growth solution , sodium citrate as a ligand under the conditions of core-shell nanoparticles synthesized silver . Through control of the reaction conditions , high yields , the tunable spectral range of the composite silver nanoparticles. Gold and Silver Nanoparticles morphology and size of the growth rate by reducing the impact speed and great ability as a reducing agent ascorbic acid reducing the pH of the reaction system , and the concentration of ascorbic acid itself , so changing the pH or the concentration of ascorbic acid fellowship silver nanoparticles growth process . The results show that at higher pH, reduction fast, easy self nucleation of silver core-shell structure is not conducive to the growth of : the low pH, the reaction rate is too slow , is not conducive to the growth of isotropic ; only when the medium pH silver uniform growth surface of the particles into a continuous shell . On the other hand , ascorbic acid concentration is too low , you can not restore a sufficient amount of silver ; while ascorbic acid is too high , there are silver since nucleation occurs . By regulating the pH and the concentration of ascorbic acid prepared with different amount of silver deposited and the different thickness of the shell of the composite silver nanoparticles.
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