Roselle-mediated green synthesis optimization and characterization

Silver nanoparticles (AgNPs) are widely recognized for their unique physicochemical and antimicrobial properties, yet conventional synthesis routes often raise environmental concerns. This study establishes a green and reproducible method for AgNP synthesis using Roselle (Hibiscus sabdariffa) extract as both a reducing and stabilizing agent. The synthesis process was systematically optimized by varying pH, temperature, incubation time, AgNO3 concentration, and extract volume. Characterization was performed using UV – Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDX), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). The optimized conditions were identified as pH 11, 40°C, 2 mM AgNO3, 10 mL extract, and 48 h incubation, producing stable AgNPs with a surface plasmon resonance peak at 444 nm. TEM analysis revealed predominantly spherical nanoparticles ranging from 12 to 40 nm, while FESEM showed larger aggregated features (42–89 nm). EDX confirmed elemental silver with minimal impurities, and FTIR indicated the involvement of polyphenols and flavonoids in nanoparticle reduction and capping. These findings demonstrate that Hibiscus sabdariffa is an effective biogenic platform for producing stable, nanosized silver nanoparticles under optimized green synthesis conditions, highlighting their potential for biomedical applications.