Green synthesis of silver nanoparticles using Onobrychis sativa L.: Characterization, catalytic degradation of methylene blue, antioxidant activity, and quantitative analysis of bioactive compounds

The synthesis of silver nanoparticles was achieved using Onobrychis sativa extract of leaves and flowers mixture and their structures were characterized by spectroscopic study. The appearance of maximum absorption at 442 nm in UV-Vis spectroscopy verified the silver nanoparticles (AgNPs@Os) structure. The functional groups of natural compounds in O. sativa acting as reducing and stabilizing agents were presented by FTIR. The typical signal appeared at 3211 cm-1 belonging to the OH moiety. The diffraction peaks by X-ray XRD analysis (2 & theta;) at 38.16 degrees, 44.31 degrees, 64.49 degrees ,77.38 degrees, and 81.52 degrees may relate to 111, 200, 220, 311, and 222 facets presenting the face-centered cubic unit structure (fcc). The stability of AgNPs@Os was determined by zeta potential as - 34.2 mV. Moreover, the histogram of DLS revealed the average size of nanoparticles in suspension. TEM analysis displayed that AgNPs@Os were quasi-spherical and the average magnitude was 14.7 nm. The intense peak at 2.5-3.5 keV in EDX spectrum approved the structure of the nanoparticles. The catalytic degradation of methylene blue by sodium borohydride in the presence of AgNPs@Os as a catalyst was investigated and degradation was found to be 68 % in 30 min. Antioxidant activity of extract and AgNPs@Os was conducted using the DPPH & BULL; free radical scavenging, ABTS & BULL;+ radical cation scavenging, FRAP, and superoxide anion radical scavenging assays. AgNPs@Os exhibited excellent activity. Quantitative analysis of bioactive compounds in water extract was carried out by HPLC after nanoparticles synthesis and gallic acid was found as a major compound.