Kinetics for an Optimized Biosynthesis of Silver Nanoparticles Using Alfalfa Extracts

Abstract

Abstract In recent years, great efforts have been directed to provide eco-friendly methods for nanoparticles (NPs) synthesis. In this endeavor, it is desired that polydispersity be as narrow as possible and that the chemical and physical properties can be controlled. In this work, silver nanoparticles (SNPs) were obtained by means of (a) a green approach (biosynthesis) using alfalfa extracts; and (b) a thermal decomposition method in organic media. As per biosynthesis, pH, initial concentration of precursor (Ag+) and extraction solvent of plant metabolites were varied in order to identify the conditions where SNP polydispersity presented a best value. When these conditions were determined, the reaction kinetics was evaluated. The rate constant and order of reaction were 7.33×10−6 L3.6/mol3.6 s, and 4.6, respectively. Also, in the biosynthesis, it was found that the size and the degree of polydispersity depend on initial concentration of precursor and the type of extractant. Thermal decomposition was performed using silver oleate as precursor in order to compare characteristics of the NPs obtained by both biosynthesis and the chemical method. According to our results, SNPs obtained through thermal decomposition showed a lower polydispersity and higher degree of crystallinity than those obtained using biosynthesis. However, the green method eliminates the use of toxic compounds, which is extremely important if these particles are intended for biomedical purposes. In addition, this is a less expensive method as compared to other chemical methods. To our knowledge, this is one of the few reports analyzing the reaction kinetics, which is extremely important if scale-up is intended.