Green Chemistry Approaches for the Sustainable Synthesis of Nanomaterials: Biogenic Routes, Characterization, and Application Prospects

Abstract

The present review is a critical review of green chemistry-based pathways for the sustainable production of nanomaterials, with a specific focus on biogenic and environmentally friendly approaches. The discussion begins by defining the fundamentals of nanomaterials synthesis and contrasting conventional top-down and bottom-up methods with green principles. Common methods used in the literature, such as sol-gel, hydro/solvothermal synthesis, chemical vapor deposition, and microemulsion, typically use hazardous precursors, toxic organic solvents, and conditions of high energy consumption, which are inconsistent with waste prevention, safer solvents, and energy conservation. The paper further investigates how the concept of green chemistry, particularly the use of less hazardous solvents and auxiliaries, renewable feedstocks, catalysis, and naturally safer design, has been transformed into real-world plans, such as plant- and microbe-mediated synthesis, aqueous and solvent-free reactions, and process synthesis (mixtures using a microwave, ultrasound, or mechanochemistry). The consideration is on how the natural reducing and capping agents (phytochemicals, polysaccharides, proteins, and microbial metabolites) control the nucleation, growth, particle size, morphology, and colloidal stability and how the systems can reduce toxicity and enhance atom economy at the same time. The review also outlines the main characterization methods—UV-Vis, FTIR, XRD, TEM/SEM, DLS, and zeta potential—and how to use these methods to verify the successful green synthesis, clarify surface chemistry, and correlate structure and surface properties to the catalytic, environmental, and antimicrobial activity. Lastly, the paper concludes with a synthesis of the existing literature on environmental, economic, and safety concerns; highlights the key challenges, including scalability, reproducibility, and incomplete mechanistic knowledge; and provides the future directions of process intensification, life cycle-based sustainability measures, and the implementation of green nanomaterial synthesis in the context of a circular economy and industry.