Nanoarray-fortified ultra-durable nanofiber membrane via sequential crystallization

Advanced polymeric nanofiber membranes (PNMs) are hindered by intrinsically low mechanical strength and stability, especially under harsh conditions of oily water separation. Here, we report an approach to simultaneously enhance the tensile strength, stability and hydrophilicity of PNMs by sequentially crystallizing the covalent organic framework (COF) and poly(ether-etherketone) (PEEK). During the process, a superhydrophilic pine-needle-shaped COF nanoarray layer is inserted into the PEEK nanofibers to form a mechanical interlocking structure through the entanglement between PEEK non-crystallizing polymer chains and the hetero-interpenetration crystal structure consisting of COF crystal and PEEK crystal regions. Both simulation and experimental results show that the mechanical interlocking structure enhances the mechanical properties (16.2 MPa) and harsh-condition stability of the PNMs. In addition, the rigid COF nanoarray layer significantly improves the affinity with water, thereby enhancing the emulsion permeance up to 3.4 ×10⁴ L m^-2 h^-1 bar^-1 (968% increment) with nearly zero irreversible fouling during 100 fouling-cleaning cycles, which exceeds that of the state-of-the-art membranes.