Synthesis of silver nanoparticles using Hypericum scabrum extract: improve particle size distribution to achieve uniform particle sizes
摘要
Controlling the size and uniformity of nanoparticles is critical for their application in various fields. In this study, the extract of Hypericum scabrum, a species known for its rich phytochemical content, was used as both a reducing and stabilizing agent to produce silver nanoparticles (AgNPs). Design-Expert software was employed to design and analyze experiments, aiming to optimize the synthesis conditions to achieve AgNPs with consistent and uniform particle sizes. The optimum conditions, determined by a low polydispersity index (PDI) and minimum error criteria, were 1.169 mM AgNO3, 40.9 °C, pH 5.89, and a reaction duration of 23.43 h, resulting in a PDI of 0.058 and confirming the achievement of monodispersity in AgNPs. Under these conditions, the AgNPs exhibited 81.3% free radical scavenging efficiency. The nanoparticles were fully characterized. UV–Vis spectroscopy showed a surface plasmon resonance band at 426 nm, confirming AgNP formation. X-ray diffraction (XRD) analysis revealed four characteristic peaks at 2θ ≈ 38.84°, 46.36°, 64.64°, and 78.02°, corresponding to the (111), (200), (220), and (311) planes of face-centered cubic silver. Fourier-transform infrared (FTIR) spectroscopy identified key functional groups on the nanoparticle surface, including O–H and C–H stretches (broad band ~ 3400 cm⁻1 and peaks at ~ 2900 cm⁻1), C=O and C=C stretches (~ 1700–1600 cm⁻1), and metal–ligand bands (600–700 cm⁻1), indicating capping by plant metabolites. The average crystallite size calculated using the Debye–Scherrer equation indicated predominantly spherical AgNPs of approximately 20 nm in diameter. Notably, the AgNPs remained well-dispersed over time, reflecting the negative surface charge imparted by adsorbed phytochemicals.