Incorporating etched ZnO nanoparticles to fabricate positively charged composite membrane for heavy metal removal

The removal of heavy metal ions by nanofiltration (NF) membranes is attractive, but it is limited by a trade-off effect between permeation and solute rejection. Generally, the permeability of the NF membrane is closely related to its hydrophilicity, while the solute rejection is closely related to size exclusion and the Donnan effect. In this study, porous etched zinc oxide (ZnO) nanoparticles were prepared through alkali etching, and a thin-film nanocomposite (TFN) NF membrane was fabricated by interfacial polymerization (IP) method between PEI and TMC on a polysulfone (PSF) substrate. The incorporation of 0.01 wt% etched ZnO nanoparticles increased the hydrophilicity and positive charge of the NF membrane, resulting in an increase in the permeability (from 6.0 L m−2 h−1 bar−1 to 8.1 L m−2 h−1 bar−1) and rejection of heavy metal ions (Cu2+, Zn2+, and Ni2+ increased from 85 % to over 96 %). Long-term filtration experiments using the simulated wastewater demonstrated that the prepared NF membrane exhibited good stability and had the potential for industrial applications. It opens a new pathway for studying TFN NF membranes, indicating that alkaline etching can transform smooth nanoparticles into nanoparticles with higher specific surface area and porosity, thereby improving the performance of membranes.