Eco-friendly fabrication of silver nanoparticles from Echinops species: a comparative study of antibacterial and photocatalytic performance

Abstract

The green synthesis of metal nanoparticles (NPs) has been of growing interest, in part because it is environmentally friendly, less toxic, and uses plant-derived phytochemicals as natural reducing and stabilizing agents, providing a more sustainable approach to traditional chemical synthesis. This study reports the green synthesis of silver NPs (Ag NPs) from aqueous leaf extracts of Echinops ritro and Echinops spinosus and assesses the comparative antibacterial and photocatalytic properties. The optical band gap energies of Ag NPs grown using both plants were determined to be 2.76 eV and 2.78 eV, respectively. FTIR, SEM, and XRD analyses have identified the functional groups in the formation of polydisperse NPs and validated their size and crystalline structure. The synthesized Ag NPs-ES demonstrated the best antibacterial activity with a maximum inhibition zone (24.66 mm) against S. aureus. In comparison, the zone of inhibition (ZOI) against other strains was 24 ± 1, 21.66 ± 0.88, and 21 ± 0.57 mm for B. licheniformis, B. Subtilis, and E. coli, respectively, while Ag NPs-ES showed the same trend in the maximum ZOI against S. aureus (22.33 ± 0.33 mm), followed by B. subtilis (20.66 ± 0.66 mm), B. licheniformis (15.33 ± 0.88 mm), and E. coli (15 ± 0.57 mm). The photocatalytic degradation of methylene blue (MB) and methyl orange (MO) dyes under sunlight was more prominent with Ag NPs from E. spinosus (80% & 88%) than from E. ritro (71.2% & 74.8%), following pseudo-first-order kinetics with higher rate constants. The results supported that E. ritro and E. spinosus-capped Ag NPs are potent, environmentally friendly materials with potential applications in antibacterial formulations and wastewater treatment.