From ultrafiltration to nanofiltration: Hydrazine cross-linked polyacrylonitrile hollow fiber membranes for organic solvent nanofiltration

Ultrafiltration-level polyacrylonitrile (PAN) hollow fiber membranes were molecularly engineered via chemical cross-linking to obtain membranes suitable for use in organic solvent nanofiltration (OSN). By adjusting the dope composition and spinning conditions, hollow fibers possessing a desirable sponge-like cross-section with minimal macrovoids were obtained. Hydrazine monohydrate was used as the cross-linker and the effects of cross-linking time on the membrane's separation performance were investigated. X-ray photoelectron spectroscopy was used to elucidate the possible reactions and indicated the successful cross-linking of the PAN hollow fiber membranes. The cross-linked nanofiltration-level hollow fibers were subjected to OSN tests using ethanol and dyes as model feed solutions. With this simple and effective modification, the PAN hollow fiber membranes were able to achieve a pure ethanol permeance of 2.32 L m⁻² h⁻¹ bar⁻¹ and an impressive Remazol Brilliant Blue R (M_w 626.54 g mol⁻¹) rejection of more than 99.9%. Given the ease of fabrication and modification, these PAN hollow fibers represent a significant step forward in the use of hollow fiber membranes for OSN, particularly in larger-scale operations.