Metal ion-assisted fabrication of aramid nanofilm with high strength and toughness for the dye separation

Herein, Fe3+, Co2+, and Ni2+ were respectively introduced into the splitting of aramid fibers, and then the metal hydroxide nanoparticles (NPs) were formed on the aramid nanofibers (ANFs). The nanofilm assembled from NP-grafted ANFs shows high stress, toughness, and dielectric breakdown strength. The results indicate that the ANF nanofilm contained 5 wt% Fe3+ presents the highest enhancing capacity to the mechanical properties of ANF film, with a strength of 312 MPa and a toughness of 61.9 MJ m−3, increased by 73.3% and 215.8%, respectively. The NPs increase the ANF film's dielectric breakdown strength by 40.8%–60.2%. Different from the previous studies, we have not observed the densification of the nanofilm, and the enhanced mechanical properties may be caused by the strong electrostatic and coordinate interactions between NPs and ANFs, evidenced by the large numbers of fiber pull-out on fracture cross-sections. Because of the hydrophilicity of the NPs and the un-densified structures, the composite films show both high flux and rejection to methylene blue (MLB).