Chemistry of Plant Extracts Directs the Silver Nanostructures’ Crystal Structure into Hexagonally Close-Packed; A Comparative Study using Elecampane and Blueberry Extracts

In this study, silver nanostructures (AgNS) were obtained using aqueous extracts of Elecampane (Inula Viscosa) and Blueberry (Vaccinium Arctostaphylos Arctostaphylos). The synthesized AgNSs were characterized using UV-visible spectrophotometers (UV-vis), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The optimization studies revealed that pH and the extract/AgNO3 ratio played significant roles in the morphology and size of the AgNSs, while temperature did not show any significant role. Both the Blueberry and Elecampane extracts resulted in a mixture of spherical and aspherical AgNPs In contrast, utilization of a relatively high extract/AgNO3 ratio accompanied by an extended incubation period (i.e., 10 days) caused the formation of larger spherical (e.g., up to micron-sized) and large 1D AgNPs for the Blueberry and Elecampane extracts, respectively. The major difference related to the crystal structures was obtained, as the Blueberry extracts resulted in face-centric cubic (fcc) crystals, and the Elecampane extracts allowed the formation of hexagonally close-packed (hcp) crystalline structures. The AgNPs were tested for their antibacterial activities using gram (-) and gram (+) bacterial species, where the Elecampane-synthesized AgNPs possessed higher antibacterial activity that can be attributed to the hcp crystalline structure of the AgNPs.