Eco-friendly production of AgNPs by ultrasound-intensified continuous method, and process evaluation via life cycle assessment and machine learning

Owing to their excellent biocompatibility and antibacterial properties, the global annual production of silver nanoparticles (AgNPs) is estimated at 400-800 tons. Therefore, developing a green and safe approach for AgNPs synthesis is urgently required. However, the conventional AgNPs manufacturing methods required toxic reductant and higher energy consumption, which makes the reaction system harmful to humans and environment. In this study, an eco-friendly ultrasound-intensified continuous system employing minimal toxic reagents was developed. The AgNPs formation process was intensified by cavitation instead of using toxic and strong reductants. Several analytical methods were conducted to systematically investigate the mechanism and performance of as-synthesized AgNPs, such as particle size distribution, zeta potential, UV-visible absorption, morphology, yield calculation, as well as in vitro photothermal, and antibacterial. The results clearly indicated that the physicochemical properties of AgNPs could be tuned by adjusting process parameters, including temperature, feeding rate, and ultrasonic power. Specifically, the AgNPs prepared at 90 ℃, 600 W and 50 µL/min exhibited smaller size (2-5 nm) with monodisperse, spherical shape, higher yield, enhanced photothermal, and antibacterial activities. Furthermore, life-cycle assessment (LCA) and machine learning (ML) were employed to evaluate the process sustainability and identify the key influencing parameters. Comprehensive consideration of safety, experimental results, and LCA outcomes demonstrated that the ultrasound-intensified continuous method proposed in this study is superior to the traditional NaBH₄-based batch synthesis at the laboratory scale.