Razi University

The increasing spread of nanoplastic pollution in water resources, due to its high chemical stability and serious risks to human health and the ecosystem, is one of the emerging environmental crises of the present century. Among treatment technologies, polyethersulfone (PES) polymeric membranes are widely used owing to their favorable mechanical and thermal stability; however, the strongly hydrophobic nature of this polymer leads to a severe decline in flux and the occurrence of fouling. In the present study, with the aim of developing a green, sustainable, and economical solution to overcome these challenges, the surface of a PES nanofiltration membrane, after alkaline activation with sodium hydroxide, was modified using seashell bio-nanoparticles (obtained from recycling discarded seashell waste, at concentrations of 0, 0.2, 0.4, and 0.6 wt.%) combined with a bio-based crosslinking network composed of L-lysine and citric acid, via the dip-coating method.Structural analyses (FTIR-ATR, EDX, and elemental mapping) confirmed the successful formation of hydrophilic functional bonds and the homogeneous distribution of nanoparticles on the membrane surface, while scanning electron microscopy (SEM) images showed that the asymmetric structure and finger-like porous channels of the sublayer remained completely intact. Among the synthesized membranes, the membrane containing 0.2 wt.% seashell bio-nanoparticles (M-0.2), as the optimal membrane, recorded the highest performance in all evaluated indices: the water droplet contact angle decreased from 74.8° to 68.4°, the total porosity increased with a relative growth of 30.3%, from 60.71% to 79.12%, and the pure water flux increased more than threefold, from 16.02 to 49.57 kg/m²·h.In the separation test of the model polystyrene nanoplastic suspension, the M-0.2 membrane achieved a rejection efficiency of 98.94% (compared to 75.64% for the base membrane), and the outlet flow became clear. Also, in the protein filtration test, the flux recovery ratio (FRR) improved from 70.24% to 86.42%, and the irreversible fouling ratio decreased from 33% to 13%, indicating the excellent fouling resistance of the membrane. At higher nanoparticle concentrations (M-0.4 and M-0.6), particle agglomeration caused a relative decline in hydraulic properties, porosity, and separation efficiency. The findings of this study proved that the valorization of natural seashell waste combined with bio-based modifying agents, within the framework of green chemistry principles and the circular economy, is a highly effective strategy for developing a new generation of sustainable nanofiltration membranes for controlling nanoplastic pollutants in aquatic environments.