Sustainable green synthesis of silver nanoparticles using walnut septum waste: Characterization and antibacterial properties

Abstract The increasing accumulation of agricultural waste poses a significant environmental challenge, highlighting the need for sustainable waste valorization strategies. This study presents a green synthesis approach for silver nanoparticles (AgNPs) using walnut septum waste, an underutilized bioactive-rich by-product. Ultraviolet-visible spectrophotometry confirmed AgNP formation with a characteristic surface plasmon resonance band at 407 nm. Fourier-transform infrared spectroscopy, powder X-ray diffraction, and transmission electron microscopy revealed spherical, crystalline AgNPs (26–27 nm) with stability over 3 months. The antibacterial efficacy of these AgNPs was assessed against Gram-positive ( Bacillus subtilis , Staphylococcus aureus ) and Gram-negative ( Escherichia coli , Pseudomonas aeruginosa ) bacteria using the broth microdilution method. The AgNPs exhibited strong antibacterial activity, with minimum inhibitory concentrations ranging from 31.25 to 62.5 µg·mL −1 , demonstrating superior effectiveness compared to the unprocessed walnut septum extract. These findings highlight the dual benefits of repurposing agricultural waste for nanomaterial synthesis while offering an eco-friendly alternative to chemically synthesized nanoparticles. The results support the potential biomedical and environmental applications of AgNPs in antimicrobial coatings, wound dressings, food preservation, and water purification. This study provides a sustainable, cost-effective, and scalable method for AgNPs production, contributing to green nanotechnology and solid waste management.