Fabrication of tight polyamide nanofiltration membrane by using a pyridine-diamine precursor for heavy metal ions removal

Nanofiltration offers a promising solution for removing heavy metal ions from wastewater, thereby mitigating ecological and environmental risks. In this study, we synthesized a novel pyridine-diamine precursor 2,6-dipiperazine pyridine (PyBPIP), and employed it as the sole aqueous monomer to fabricate tight polyamide (PA) nanofiltration (NF) membranes via interfacial polymerization (IP) method with trimesoyl chloride for the separation of heavy metals. The resulting membrane features an ultrathin PA functional layer (approximately 60 nm), a lower molecular weight cut-off of 251 Da, and a weakly negatively charged surface. This NF membrane exhibits competitive water permeance of approximately 7.67 LMH/bar and excellent rejection rates exceeding 98 % for various heavy metals ions including Zn²⁺, Mn²⁺, Cu²⁺, along with outstanding separation performance for other divalent cations. Additionally, the NF membrane also exhibits robust stability during the 72-h operational test. In summary, this study demonstrates the feasibility of designing suitable monomers for the preparation of highly perm-selective NF membranes for the removal of heavy metal ions in wastewater.