Freshwater microalgae-mediated engineered nanoparticles: Sustainable approach for heavy metals remediation

Recently, convergence of nanotechnology and sustainable approaches has emerged as promising strategy for advanced remediation of heavy metals (HMs) from water. However, engineered nanoparticles (ENPs)-derived from freshwater microalgae gained attention as viable alternative, owing their inherent metal tolerance, rapid-growth rates, and versatile metabolic capabilities. This review predominantly focuses on freshwater microalgae-mediated-ENPs, highlighting intracellular/extracellular pathways induced by biomolecules such as polysaccharides, proteins, lipids, reductases etc., which govern nanoparticle nucleation, stabilization, and functionalization. Subsequently, the review discusses significant types of ENPs including iron, silver, gold, cadmium-sulfide, iron-oxide, nanocomposites, and bio-nano-hybrids nanoparticles, which reported removal efficiency from 21 to 100% of different HMs (lead, cadmium, chromium, copper, zinc, etc.). Despite ENPs exhibit significant potential, their large-scale implementation is constrained by challenges such as scaling-up, nutrient-variability, and high turbidity of wastewater. Future research recommended to focus on optimizing biosynthesis parameters, investigating diverse microalgal-strains, incorporating hybrid nano-materials to enhance their stability, reusability, and scalability for sustainable green-technology.