Stable Silver Nanoparticles with Narrow Size Distribution Non-enzymatically Synthesized by Aeromonas sp. SH10 Cells in the Presence of Hydroxyl Ions

Stable silver nanoparticles (AgNPs) with narrow size distribution were non-enzymatically synthesized through hydroxyl ions (OH-) assisted bioreduction of diamine silver complex with dry Aeromonas sp. SH10 cells. The effects of reaction temperature, concentrations of OH-, silver and the dry cells on the reduction of Ag ions as well as on the properties of the AgNPs were investigated. Results show that the introduction of appropriate quantity of OH- ions considerably accelerates the process. In fact, higher yields of AgNPs (> 95%) could be obtained at relatively higher initial silver concentration (1 g·L-1) with more than 1 g(Ag)·g(bio) -1 productivity of AgNPs. Plausible bioreductive mechanism is therefore proposed; wherein [Ag(NH3)2]+ ions initially reacted with OH- to form an unstable AgOH. This is then transformed into Ag2O spontaneously, and finally non-enzymatically reduced into AgNPs by the cells. Keywords: Biosynthesis, microorganisms, silver nanoparticles, hydroxyl ions