Environmental applications of silver nanoparticles: state-of-the-art review and emerging trends

Silver nanoparticles (AgNPs) possess inherent catalytic, antimicrobial, and optical properties, making them a strong candidate for environmental applications in water, air, and soil. Indeed, various reviews are available, though a significant gap persists in addressing all environmental pollutants. This review comprehensively and critically analyses the advancement in AgNP research spanning from synthesis and characterisation to practical deployment and ecotoxicological assessment. The AgNP-based systems are evaluated regarding antimicrobial disinfection, adsorptive and catalytic/photocatalytic removal of persistent organic pollutants, and integration into antifouling nanofiltration and ultrafiltration membrane technologies used for management of water pollutants. In addition, AgNPs-assisted nanosystems in fibrous filter membranes and photocatalytic composite coatings for the removal of volatile organic compounds, particulate matter, and gaseous pollutants are reviewed. Furthermore, AgNP applications for heavy metal immobilisation, organic pollutant degradation, plant disease management, and growth promotion are assessed alongside their ecotoxicological implications. Besides remediation, environmental monitoring capabilities of AgNP-based sensing platforms are systematically reviewed across five transduction modalities, including colourimetric/UV-vis LSPR, SERS, electrochemical, fluorometric, and gas sensing, covering a broad range of analytes considered as environmental pollutants. Key challenges, including nanoparticle aggregation, long-term colloidal instability, synthesis irreproducibility, ecotoxicological risks arising from Ag⁺ ion release and environmental persistence, and the current absence of harmonised regulatory frameworks for AgNP deployment, are critically discussed. This review provides a structured, evidence-based foundation for researchers and engineers working toward the responsible, scalable application of AgNP-based technologies to address contemporary environmental challenges.