The potential of Kevlar aramid nanofiber composite membranes

Kevlar aramid nanofibers (KANFs), a nanoscale version of poly(paraphenylene terephthalamide), are a fascinating class of one-dimensional organic nanomaterials with a combination of electrical conductivity, flexibility, mechanical robustness, physical stability and resistance to solvents. The interest in Kevlar aramid nanofibers with high mechanical strength is mainly due to the effectiveness of the interactions between nanofibers and matrices. They have been widely used as high-performance composites. In sharp contrast to other nanomaterials, due to their intrinsically ordered and asymmetric alternating nanostructure of molecular chains and abundant intermolecular hydrogen bonds, KANFs have received much attention in diverse fields including membrane separation technology. In recent years, research studies appeared ranging from synthesis strategies to separation application of KANF-based membranes. This review analyses and summarizes the synthesis and applications of KANF-based membranes in different processes, such as nanofiltration membranes, mixed matrix membranes, ion exchange membranes and proton exchange membrane fuel cells. Particular attention is paid to the tunable structure, chemical/physical stability, hydrophobicity/hydrophilicity and chemical reaction required in order to develop suitable KANF-based composite materials for membrane fabrication. In addition, approaches to fabricate KANF-based membranes, such as blending, grafting, amide reaction, network interpenetrating, interfacial polymerization and gel-confined conversion, are highlighted. Based on this, the application of KANF-based membranes in water treatment (including oil/water separation, water purification and desalination, emulsion separation, and dye wastewater separation), organic solvent treatment, ion separation, separation of battery and proton exchange membrane fuel cells is discussed. Finally, the advantages and disadvantages of KANF-based membranes are summarized; on this basis, the challenges and future opportunities in this field are defined. This tutorial review provides an overview of the promising potential applications of Kevlar aramid nanofibers in membrane science.