Facile synthesis of Kevlar nanofibrous membranes via regeneration of hydrogen bonds for organic solvent nanofiltration

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Polymeric organic solvent nanofiltration (OSN) membranes have gained increasing attention in OSN for their relatively low cost and ease of scaling up. However, fabrication processes are still complex, consume a large amount of aggressive solvents and sometimes even pose a safety risk in fabrication, resulting in a negative environmental impact and still having potential to lower the fabrication cost further. In this study, thin Kevlar nanofibrous organic solvent nanofiltration membranes were fabricated through a facile and green thermal treatment by using greener solvent. Instead of corrosive concentrated H2SO4, a greener solvent, i.e., a DMSO-KOH/water mixture was used to prepare a dope solution containing Kevlar nanofibers. Then, hydrogel ultrafiltration membranes were obtained from this dope solution by phase inversion. Subsequently, a facile thermal treatment in an oven was applied to transform the hydrogel ultrafiltration membrane into a solvent resistant nanofiltration membrane without consuming additional solvents and crosslinking agents by the regeneration of hydrogen bonds. The obtained nanofibrous membrane (M2%-200) has a Rose Bengal rejection of 95.4% and an ethanol permeation of 2.9 L/(m2 bar h), outperforming most other polymeric pristine OSN membranes prepared by phase inversion. This gives the Kevlar membrane a high baseline for further modification in order to increase the performance. In addition, Kevlar nanofiltration membranes maintain a relatively constant dye rejection during the filtration of a dye solution for 6 h and retain a dye rejection over 94% after being treated by different solvents for 7 days, indicating a very good solvent resistance. Moreover, this study not only provides a facile way of synthesizing Kevlar OSN membranes from a dope solution containing nanofibers, but also enables the fabrication and application of Kevlar threads in membranes by a non-corrosive and greener solvent, which may open up new insights and strategies to develop Kevlar into nanofiltration membranes.