Ion-Exchange Nanofiber Membranes for Advanced Water Treatment Applications

Challenges in clean water availability have risen over the years, and especially third world countries are in great need of localised, low-cost water purification techniques, that make use of separation membranes. Electrochemical treatments in (waste)water management show high potential in the global water resource crisis, but are often limited by the performance of the ion-exchange membrane (IEM). Low chemical resistance and fouling are major issues in the development of the next generation IEMs. An interesting choice of material for IEMs is the use of nanofibers 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. Nanofibers with an ion-exchange functionality can be produced by either pre- or post-functionalization 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. By producing IEMs from hybrid nanofibrous membranes containing both organic and inorganic parts, a wide range of different membrane properties can be obtained by altering the molecular structure. This results in IEMs with high thermal and chemical resistance as well as tunability towards a.o. mechanical properties and hydrophobicity for the use in harsh environmental conditions. For example, sulfonated silica-based nanofiber cation-exchange membranes (CEMs) offer a promising solution to the current issues of IEMs, due to their superior chemical resistance and self-cleaning properties