Nanocomposites and Nanomaterials

Kinetics and Mechanism of Green Synthesis
of Silver Nanoparticles Using the Rhamnolipid of Natural Origin
Opeida Y. O.1, Bazylyak L. I.1, Kytsya A. R.1,2,
Pokyn’broda T. Ya.1, Karpenko O. V.1
1Department of Physical Chemistry of Fossil Fuels of the Institute of Physical Organic Chemistry and Coal Chemistry named after L. М. Lytvynenko of the NAS of Ukraine.
3а Naukova Str., 79060, Lviv, Ukraine.
e-mail: bazyljak.L.I@nas.gov.ua
2Physico-Mechanical Institute named after G. V. Karpenko of the NAS of Ukraine.
5 Naukova Str., Lviv, 79060, Ukraine
Widespread use of synthetic antimicrobial drugs leads to the development of antibiotic resistance of pathogenic strains of microorganisms. Therefore, today the researchers are very interested in drugs based on nanoparticles of metals, in particular silver, which has antibacterial, antifungal and antiviral activity. A critical analysis of the results of research performed in recent decades has shown that despite the large number of references devoted to the study of properties, use and development of methods for obtaining the silver nanoparticles, the influence of kinetic parameters on their characteristics is insufficiently studied. In presented work silver nanoparticles (AgNPs) have been synthesized by “green synthesis” method using the silver nitrate as precursor and surface-active rhamnolipid (RL–1) of natural origin, which represents by itself the product of microbial synthesis of the strain Pseudomonas sp. PS–17 and was used as reducing agent and stabilizer. The kinetics of green synthesis of AgNPs via reduction of Ag+ ions by RL–1 was studied in details using the UV–vis spectroscopy. It was found, that kinetic curves are sigmoidal and can be fitted using the Finke-Watzky 2–step mechanism (FW–2) and the rate constants of nucleation and growth of AgNPs were estimated. The extreme dependencies of kinetic parameters of nucleation and growth of AgNPs on pH of reaction mixture and temperature were observed. That is why the thermodynamics of interaction of Ag+ and RL–1 was studied using the semiempirical quantum chemical method PM–7. It was found that the reduction of Ag+ to Ag0 may result to the formation of keto-rhamnose group in RL-1. Tentatively such reaction may occur via formation of alkoxide intermediate [1] which is illustrated by extreme dependence of the rate of AgNPs formation on pH, but such assumption need to be more detailed studied.
1.	 Gomes J. F., Garcia A. C., Ferreira E. B., Pires C., Oliveira V. L., Tremiliosi-Filho G., Gasparotto L. H. New insights into the formation mechanism of Ag, Au and AgAu nanoparticles in aqueous alkaline media: alkoxides from alcohols, aldehydes and ketones as universal reducing agents. // Phys Chem Chem Phys. - 2015. - 17(33). - P. 21683-21693.
This work was performed under the partial financial support via the project № 165/02.2020 from the National Research Foundation of Ukraine.