A review on ion-exchange nanofiber membranes: properties, structure and application in electrochemical (waste)water treatment

In view of today's challenges in clean water depletion and wastewater management, electrochemical water treatment processes are increasingly applied for e.g. desalination of brackish water, recovery of resources and energy production from waste streams, and disinfection of wastewater. These electrochemical processes typically make use of an ion-exchange membrane in between the anode and cathode. The choice of material for this membrane is crucial for the performance of the cell and often its performance is the key bottleneck. Over the last decade, research has been focused on the production of ion-exchange nanofibers as membrane material due to their outstanding ionic properties as a result of their specific morphology. Nanofiber membranes are known to have a large specific surface area, flexibility, high porosity and interconnected pores. Different strategies are applied for the production and structural design of these ion-exchange nanofiber membranes, which are discussed in this review. Nanofibers with an ion-exchange functionality can be produced by either pre-or postfunctionalization methods, combined with electrospinning. Depending on the application, these nanofiber mats can be used as such, or further membrane processing is possible to improve the dimensional stability, typically by adding a pore-filling matrix in between the nanofibers. Eventually, the current state of research on ion-exchange nanofibers in electrochemical separation and degradation applications is discussed. The many examples highlighted in this review prove the potential of nanofibers as ion-exchangers and provide insights for future research in this area.