Multi-round Recycling of Green Waste for the Production of Silver Nanoparticles: Synthesis, Characterization, and Biological Activity

Due to the limitations of conventional synthesis and the growing utilization of nanoparticles, recent efforts have shifted to green approaches such as utilizing plant waste extracts. A novel initiative to repurpose household and agricultural green waste for the generation of silver nanoparticles (AgNP) offers a sustainable, low-cost alternative that addresses environmental and economic concerns. In this context, we aimed to evaluate the multi-round recyclability of <i>Coffea arabica</i> (CA), green tea (GT), and Virginia creeper (VC) waste for AgNP production, then conduct a comprehensive physicochemical and bioactivity characterization of the nanoparticles. The study was designed to prepare AgNPs using waste from CA, GT, and VC generated by one, two, and three rounds of leftover extractions, then the obtained nanomaterials were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), and X-ray powder diffraction (XRD). Their toxicity on malignant and nonmalignant human cells was evaluated by viability assays, the antimicrobial performance was assessed on Gram-positive, Gram-negative bacteria and against <i>Cryptococcus neoformans</i> and <i>Aspergillus niger</i> by microdilution method. The production of reactive oxygen species (ROS) was examined by a staining method, and the AgNP-related silver ion release was measured by inductively coupled plasma mass spectroscopy. Our findings confirmed successful synthesis of AgNPs utilizing recycled waste materials; nevertheless, the plant type and extraction round influenced AgNP properties to a unique combination of nanoparticle size and stability. All AgNPs showed strong toxicity against human cancer cells, albeit affecting also noncancerous fibroblasts. GT-derived AgNPs exerted potent antibacterial activity, while those by VC had strong antifungal effects. The observed bioactivity correlated with the increasing number of extraction cycles and was the result of enhanced silver ion-releasing capability that culminated in increased ROS levels. These findings demonstrate the viability of multi-round extract recycling for sustainable AgNP synthesis and suggest potential applications in industrial fields such as antimicrobial air filtration systems.