Development of novel nanofiltration membrane via cross-linking a natural polymer and its application in heavy metals removal from groundwater

The toxic heavy metals constitute a threat to the groundwater supply. Nanofiltration (NF) membranes play a crucial role in water purification, particularly for the separation of divalent and trivalent ions from contaminated water. However, the negative electrostatic property of prevalent polyamide nanofiltration (NF) membranes poses a challenge in removing positively charged heavy metals. Herein, we developed a high performance cross-linking NF membrane based on modified chitosan oligosaccharide (MCOS) and polyethyleneimine (PEI). Benefiting from sufficient positive charges obtained by PEI, the optimal PEI/L-MCOS NF membrane exhibited high rejection rate (98.39 % for Fe 3+ , 95.14 % for Zn 2+ and 93.32 % for Cu 2+ ). Specially, for simulated groundwater with slight heavy metal contamination (≤10 ppm), the membrane can easily reduce the content to a level below the standard set by the World Health Organization (WHO) within a broad pH range. The ultrathin separation layer and fine transport channels endowed membrane excellent pure water flux (9.24 L m −2  h −1 ·bar −1 ). Due to the stable covalent connection between MCOS and PEI, the membrane revealed favorable long-term stability. Moreover, different molecular weights of MCOS adjusted the pore size of the membrane and distance between polymer chains, thereby controlling its structure and performance. Overall, utilizing natural polymer to fabricate high performance NF membrane in this work provides a promising approach for groundwater purification.