Preparation of polyethylene based composite nanofiltration membrane and its application in removal of heavy metals for water purification

The commercial polyethylene (PE) battery separator is well-suited as support for nanofiltration owing to its thickness of 7 um, high porosity, and strong mechanical properties. A new polyethylene based thin-film composite membrane was fabricated on the catechol/polyethyleneimine (CCh/PEI) modified PE support by pre-diffusion interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC). By regulating the properties of the CCh/PEI layer and the PIP to influence the diffusion of PIP, a distinct worm-like structure in the polyamide (PA) layer was found, which provides more water penetration sites. After grafting melamine on the surface of PA layer, the TFC membrane exhibited outstanding chlorine resistance and the permeability of 12.5 L·m−2·h−1·bar−1 with the Mg2+ rejection of 94.5 %. Due to its small pore size, strong positively charged, and high adsorption capacity, the TFC membrane showed high rejection of heavy metal ions through pore size sieving, Donnan effect and adsorption. Therefore, it has great potential for water purification from heavy metal ions.