Green Extract-Mediated Synthesis of Metallic Nanoparticles Assisted by Ultrasound: A Critical Review for Environmental Applications

Abstract

In this review, the use of green extracts and ultrasound (US) for the synthesis of metallic nanoparticles (MNPs) for environmental applications is described, covering studies published from 2015 to 2025. Currently, the synthesis of MNPs constitutes a consolidated field of research, with strategic interest for companies and for environmental applications. Although well-established, traditional synthetic methods for MNPs often have environmentally friendly limitations, including the use of potentially toxic reagents and high energy consumption. In response, green chemistry approaches based on plant extracts have emerged as sustainable alternatives that minimize the consumption of hazardous reagents, aligning with the principles of green chemistry. Ultrasound has emerged as an efficient and suitable alternative for MNPs production, presenting advantages over existing methods. The synergistic integration of plant extracts with US not only accelerates reaction kinetics but also improves nanoparticle stability, crystallinity, and size distribution compared to conventional methods. In this review, the advances in green synthesis are discussed, highlighting the contribution of plant extracts to the reduction and stabilization of MNPs, and the synergistic role of US in enhancing synthesis efficiency. The mechanisms underlying nanoparticle formation are discussed, and the key US parameters (frequency, amplitude, acoustic power density, and application time) that influence particle characteristics were evaluated. Furthermore, this review highlights the main environmental applications of MNPs and critically examines current challenges and future prospects in the field. The goal is to provide a valuable and comprehensive reference to support and guide future research and technological developments involving green synthetic routes.