Comparative evaluation of silver nanoparticles synthesized via Gracilaria corticata, Citrus limon, and NaBH₄: mechanistic, optical, and functional insights

Abstract

Green synthesis of silver nanoparticles (AgNPs) using Gracilaria corticata extract was conducted and compared with AgNPs synthesized chemically (NaBH₄) and phytogenically (Citrus limon). All syntheses were performed without surfactants or synthetic stabilizers. The G. corticata-AgNPs exhibited a red-shifted SPR peak (433 nm), broader size distribution (25–38 nm), and predominantly spherical morphology with occasional faceted features, consistent with Mie theory predictions. Photoluminescence quenching and UV–Vis analysis indicated enhanced charge separation and light-harvesting potential. Functionally, these AgNPs achieved > 90% degradation of methylene blue (certified dye, ≥ 82%) under sunlight and showed strong antibacterial activity against Escherichia coli, Citrobacter koseri, and Staphylococcus aureus (zone of inhibition up to 20.3 mm). This study provides mechanistic and functional insights into marine algal-mediated AgNP synthesis and highlights its advantages for sustainable biomedical and environmental applications.