Positively charged thin-film nanocomposite membrane doped with functionalized covalent organic frameworks nanosphere for heavy metal ion removal

Discharging industrial wastewater containing heavy metal ions presents a significant risk to the ecological system and human health. Due to the combined effects of electrostatic repulsion and size exclusion, positively charged nanofiltration membranes demonstrate considerable potential for application to remove heavy metals. In this study, well-dispersed and amino-rich positively charged COFs-PEI nanospheres were initially prepared by modifying covalent organic frameworks (COFs) nanospheres with polyethyleneimine (PEI). Subsequently, a positively charged thin-film composite (TFN) membrane (COFs-PEI/TFN membrane) was prepared through interfacial polymerization, following of doping the material mentioned above into the aqueous phase. Furthermore, the surface of the COFs-PEI/TFN membranes exhibited enhanced hydrophilic properties and a higher positive charge density. The COFs-PEI/TFN membranes exhibited excellent separation performance for heavy metal salt solutions, with the rejection up to 98.6 %, 97.8 %, 97.3 %, 96.4 %, and 95.9 % for Fe 3+ , Cu 2+ , Ni 2+ , Mn 2+ , and Zn 2+ , respectively, as well as with permeability maintained above 23.5 L‧m −2 ‧h −1 ‧bar −1 . Moreover, COFs-PEI/TFN membranes can maintain their excellent heavy metal ion separation performance in a high-concentration heavy metal ion solution, under high operating pressure, and long-term operating conditions. Therefore, it has a broad application potential in removing or recovering heavy metal ions in industrial wastewater.