Optimization, Green Synthesis, and Comprehensive Characterization of Silver Nanoparticles Using Plant Extracts
Abstract
Green synthesis of silver nanoparticles (AgNPs) using plant-derived reducing agents offers a sustainable, non-toxic, and cost-effective alternative to conventional physicochemical fabrication methods. This study presents the systematic optimization, biogenic fabrication, and exhaustive physicochemical characterization of AgNPs synthesized using aqueous leaf extracts of Azadirachta indica (neem), Ocimum sanctum (tulsi), and Aloe vera as dual-function bioreductants and capping agents. Eight formulations (F1–F8) were designed by varying silver nitrate (AgNO3) concentration (1.0–2.0 mM), extract volume ratio (10–20% v/v), reaction pH (7–10), and temperature (25–80°C). Comprehensive characterization was performed using UV-Visible spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDX), Zeta potential analysis, Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC)1,2. The optimized formulation F5 (A. indica extract, 1.5 mM AgNO3, 15% v/v, pH 9, 60°C) yielded monodisperse, predominantly spherical AgNPs with a characteristic Surface Plasmon Resonance (SPR) peak at 428 nm, mean hydrodynamic diameter of 18.3 nm, polydispersity index (PDI) of 0.198, and zeta potential of −38.4 mV, indicative of excellent colloidal stability3. XRD confirmed face-centered cubic (FCC) crystallinity with a Scherrer crystallite size of 14.2 nm. FTIR analysis revealed phytochemical functional groups (hydroxyl, carbonyl, amine) involved in reduction and surface capping. Broad-spectrum antimicrobial evaluation demonstrated potent activity against Staphylococcus aureus, Escherichia coli, and fungal pathogens. Antioxidant (DPPH IC50 = 84.6 μg/mL) and photocatalytic degradation of methylene blue (91.4% efficiency, 120 min) further established the multifunctional utility of optimized AgNPs4,5. This investigation provides a robust, reproducible green synthesis platform applicable to pharmaceutical, biomedical, and environmental remediation contexts.