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.