Preparation of positively charged nanofiltration membranes: Manipulation of the positive charge

Positively charged nanofiltration membranes offer significant advantages in separating positively charged substances. The key to developing high-performance positively charged nanofiltration membranes lies in the acquisition and modulation of positive charge during membrane preparation. This review provides a review of recent literature on the preparation and application of positively charged nanofiltration membranes. The preparation methods of positively charged nanofiltration membranes were firstly summarized, including interfacial polymerization, phase conversion, self-assembly, co-deposition, chemical cross-linking, filtration deposition, etc. In addition, the main applications of positively charged nanofiltration membranes are presented, such as magnesium‑lithium separation, lithium recovery from the spent lithium-ion batteries, heavy metal removal, nuclear wastewater decontamination, hardness ion removal, dye separation, micropollutant removal and other emerging separation areas. This review focuses on the generation and manipulation strategies of positive charges in different preparation processes. The existing challenges and future directions in this field were also discusses. The review aims to provide guidance and inspiration for the preparation and application of positively charged nanofiltration membranes.