Biosynthesis of silver nanoparticles using leaves of Stevia rebaudiana

The synthesis of silver nanoparticles employing a shadow-dried Stevia rebaudiana leaf extract in AgNO3 solution is reported. Transmission electron microscopy and X-ray diffraction inspections indicate that nanoparticles are spherical and polydispersed with diameters ranging between 2 and 50 nm with a maximum at 15 nm. Ultraviolet-visible spectra recorded against the reaction time confirms the reduction of silver nanoparticles indicating that the formation and the aggregation of nanoparticles take place shortly after the mixing, as they persist concurrently with characteristic times of 48.5 min and 454.5 min, respectively. Aggregation is found to be the dominant mechanism after the first 73 min. Proton nuclear magnetic resonance spectrum of the silver nanoparticles reveals the existence of aliphatic, alcoholic and olefinic CH2 and CH3 groups, as well as some aromatic compounds but no sign of aldehydes or carboxylic acids. Infrared absorption of the silver nanoparticles suggests that the capping reagents of silver and gold nanoparticles reduced in plant extracts/broths are of the same chemical composition of different ratios. Ketones are shown to play a somehow active role for the formation of nanoparticles in plant extracts/broths. (C) 2011 Elsevier B.V. All rights reserved.