Green Nanomaterials From Biological Resources for Sustainable Water Treatment and Environmental Remediation

The increasing contamination of aquatic environments by persistent organic and inorganic pollutants has intensified the need for sustainable and environmentally responsible water‐treatment technologies. Green nanotechnology offers a promising route for producing functional nanomaterials from biological resources while reducing reliance on hazardous chemicals and energy‐intensive synthesis. This review critically examines recent advances in the biological synthesis of metallic, metal‐oxide, and composite nanomaterials using plants, bacteria, fungi, algae, and agro‐industrial residues, with emphasis on the roles of biomolecules in nanoparticle nucleation, growth, stabilization, and surface functionalization. The relationships between biological precursors, synthesis conditions, physicochemical properties, and remediation performance are discussed, followed by a critical assessment of applications in the removal and transformation of dyes, phenolic compounds, pesticides, pharmaceutical pollutants, and heavy metals from aqueous environments. Particular attention is given to adsorption, photocatalytic, catalytic, and advanced oxidation mechanisms, together with catalyst recyclability and transformation products. Key challenges affecting practical implementation, including synthesis reproducibility, nanoparticle recovery, metal leaching, catalyst regeneration, scale‐up, and limited validation in real wastewater, are critically evaluated. Environmental safety and life‐cycle considerations are also addressed, emphasizing nanomaterial toxicity, secondary pollution, environmental fate, and the need for integrated risk assessment. Finally, future research priorities are proposed, including standardized synthesis and reporting protocols, mechanism‐guided material design, real‐wastewater and pilot‐scale validation, and life‐cycle, techno‐economic, and environmental risk assessment. Biologically derived nanomaterials offer substantial potential for sustainable water purification and environmental remediation; however, their practical implementation requires an integrated assessment of treatment performance, scalability, economic viability, and environmental safety.