Silicification-interlayered nanofiber substrates regulated crumpled ultrathin polyamide nanofilms for highly enhanced nanofiltration

Abstract

Thin-film nanofiber composite (TFNC) membranes have shown great potentials for highly efficient nanofiltration. However, it remains a challenge to construct defect-free ultrathin polyamide nanofilms with designed crumpled structures on polymeric nanofiber substrates via traditional interfacial polymerization (IP) to realize high permeability and selectivity synchronously. Herein, a novel strategy is reported to regulate the polyamide nanofilm by a silicification-interlayered nanofiber substrate with hydrophilic and rugged surface. The silica interlayer could enrich piperazine (PIP) monomers in aqueous solutions and control the releasing towards the interfacial reaction zone, enabling the homogeneous IP reaction and the reduced thickness of PA nanofilms. The silicified nanofiber substrate can also serve as a templating support to crumple the PA nanofilms and thus increase their effective infiltrating area. Furthermore, deep insight has been taken into the intermolecular interactions in the IP system and the fundamental mechanism of the silicification-interlayered nanofiber substrate regulating the IP process via density function theory (DFT) and dissipative particle dynamics (DPD) simulations. The membrane morphologies were observed by SEM and AFM, and chemical structures of membrane surfaces were characterized by FTIR/ATR, XPS and XRD in detail. The hydrophilicity and charged properties of different membrane surfaces were analyzed by water contact angle and Zeta potential tests, respectively. As a result, an ultrathin crumpled PA nanofilm is generated on top of the nanofiber substrate as selective layer, enabling the composite membrane with enhanced water permeability of 19.6 L m−2 h−1 bar−1 (approximately two folds higher than that of the pristine PA membranes) and high Na2SO4 rejection of 96.5%. Meanwhile, the prepared membranes reveal good structural stability not only under different operation pressures but also during long-term filtration processes. This work is believed to provide a facile approach to engineer advanced TFNC membranes with high-efficiency nanofiltration performance.