Green Synthesis of Nanoparticles for Environmental Applications: Advances, Limitations, and Comparative Assessment

Abstract

Green synthesis has gained attention as a sustainable approach for producing nanoparticles using biological materials under comparatively mild reaction conditions. This mini-review examines plant-mediated synthesis of inorganic nanoparticles and their potential applications in environmental remediation. It discusses the major synthesis routes for nanoparticles, including physical, chemical and green methods, and compares them in terms of cost, energy demand, toxicity, particle control, scalability and environmental compatibility. Particular attention is given to plant extracts as sources of phytochemicals, including polyphenols, flavonoids, terpenoids, alkaloids, organic acids and polysaccharides, which may act as reducing, capping and stabilising agents during nanoparticle formation. This review also summarises major classes of green-synthesised nanoparticles, including iron-based, silver, gold, zinc oxide, copper, titanium dioxide, palladium, selenium and magnesium oxide nanoparticles. Their reported environmental applications include dye degradation, heavy-metal removal, wastewater treatment, photocatalysis, antimicrobial activity and organic pollutant remediation. Iron-based nanoparticles are emphasised because of their abundance, magnetic properties, redox activity and reported usefulness in pollutant removal. The review further highlights important limitations of green synthesis, including variability in biological raw materials, low or inconsistent yield, limited control over particle size and morphology, agglomeration, incomplete mechanistic understanding, scale-up barriers and insufficient ecotoxicological assessment. Overall, green synthesis is presented as a promising route for developing environmentally relevant nanomaterials; however, wider application requires improved standardisation, careful characterisation, realistic wastewater testing, recovery strategies and safety evaluation.