Constructing antimicrobial membrane surfaces with polycation–copper(II) complex assembly for efficient seawater softening treatment

In this study, a facile and novel strategy for constructing tunable antimicrobial NF membrane surface was developed by a simple electrostatic assembly of polycation–copper(II) complex on the polyacrylonitrile substrate surface followed by cross-linking. Polycation–copper(II) complex with high stability and charge density, using polyethyleneimine (PEI) as a capping ligand, was formed by exquisitely manipulating the pH and Cu 2+ concentration for strong assembly on the surface. We confirmed that PEI–copper(II) complex assembly was a good way to significantly improve the Cu 2+ loading efficiency in terms of loading time and loading amount with AAS and EDS measurements. We also demonstrated that cross-linking had a significant influence not only on the strong assembly of PEI–Cu(II) complex to the substrate surface but also on the controllable Cu 2+ release, which was confirmed by SEM, EDS and AAS measurements after exposing the NF membrane to bath sonication and real seawater. The NF membrane exhibited significant antimicrobial activity with antibacterial efficiency of more than 95% and prevented effectively the formation of biofilms for up to 6-month test. For real seawater softening, the NF membrane achieved approximately 32.3   L/m 2   h flux and 43.5%, 68.3%, 98.1%, 19.1% and 18.7% rejection of salt, SO 4 2− , Mg 2+ , Na + and Cl − , respectively, with a high softening efficiency (low S value) compared to other commercial NF membranes. We hope that the present method can be developed as a competitive technology for the fabrication of robust and versatile antimicrobial membrane, leading to the high efficiency of seawater softening.