Synthesis of silver nanoparticles with remediative potential using discarded yerba mate: An eco-friendly approach

Silver nanoparticles (Ag-NPs) applications are strongly dependent on their stability against aggregation. In the present work, environmentally-friendly Ag-NPs were synthesized by a simple and efficient procedure, using discarded yerba mate extract (DYME) as a reducing and capping agent. The Ag-NPs thus obtained (DYME-Ag-NPs) were spectroscopically characterized by ultraviolet-visible (UV-Vis) spectrophotometry, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These NPs were also evaluated for their adsorbent capacity through the adsorption isotherms using three organic substances, as well as for their antimicrobial properties on two bacterial strains. DYME-Ag-NPs were mostly spherical, monodispersed, with an average size of 24.07 +/- 3.00 nm (DLS), and proved to be stable for 70 days without any noticeable aggregation or change in size under room temperature (20-25 degrees C). The adsorption efficiency for crystal violet, methylene blue, and safranin was calculated. The adsorption data derived from the isotherm analysis fitted a Langmuir isotherm model, revealing the presence of homogeneous adsorption sites, probably coming from the DYME. Using the diffusion method, we obtained a 99.99 % growth inhibition for Escherichia coli by using 10 mu g/mL of Ag-NPs. However, no inhibition of Enterococcus faecalis growth was observed. We conclude that yerba mate waste may be used to obtain improved Ag-NPs highly stable and with a high surface area, which results in an enhanced adsorption capacity for organic compounds.