Silver nanoparticles produced via a green synthesis using the rhamnolipid as a reducing agent and stabilizer

Silver nanoparticles (AgNPs) stabilized by rhamnolipid (RL), which was separated from the supernatant of the genus Pseudomonas sp. PS-17, were synthesized. Using TEM it was found that the mean size of obtained AgNPs does not depend on the initial concentration of Ag+ but is increased with the decrease of the concentration of RL. During XRD-phase analysis it was determined, that the Ag (space group Fm-3m, Cu-structure type) is the main phase that was identified. The kinetics of the formation of AgNPs was studied in detail using the UV–Vis spectroscopy. It was observed that in all cases the kinetic curves are sigmoidal shape and are characterized by a well-notable induction period that permits to assume the homogeneous nucleation of AgNPs and their autocatalytic growth. Experimental kinetic curves were fitted using different types of Finke-Watzky schemes of continuous nucleation and fast autocatalytic growth of particles and the observable rate constants of nucleation and growth were estimated. Based on the established regularities of “green” synthesis of AgNPs stabilized by RL, the method of obtaining their colloidal solutions was optimized. A laboratory model of a flow tubular reactor for the synthesis of colloidal solutions of AgNPs has been created.