Saponin-assisted fabrication of high-performance and antifouling reverse osmosis membranes

Abstract

The applications of polyamide (PA) reverse osmosis (RO) membranes are limited by the trade-off between their separation and antifouling performance. Although antibacterial surfactants as additives have been proven effective in enhancing both the separation and antibiofouling performance of RO membranes, they are mostly petroleum-based, unsustainable, and highly toxic. Herein, we demonstrate that the introduction of saponin (SAP), a plant-derived biocompatible antibacterial surfactant, to the reaction solution during interfacial polymerization produces high-performance and fouling-resistant RO membranes. SAP increases substrate wettability with the reaction solution and promotes amine monomer diffusion by inducing Marangoni convection, thereby forming a denser and more permeable PA layer. Concomitantly, the hydrophilic SAP is embedded in the PA matrix, imparting antibacterial and enhanced hydrophilic characteristics to the resultant membrane. Hence, the membrane formed with the optimal SAP dose exhibits excellent RO performance (NaCl rejection = 99.5 ± 0.1%; water permeance = 3.3 ± 0.1 L m−2 h−1 bar−1), outperforming commercial and many lab-made RO membranes. Moreover, the membrane displays higher fouling resistance for both organic and biological foulants (flux decline ratio [FDR] = ∼17–24%; flux recovery ratio [FRR] = ∼88–95%) compared with its pristine counterpart (FDR = ∼25–32%; FRR = ∼80–87%). The RO performance and properties of the prepared membrane also remain unchanged during long-term operation owing to the robust incorporation of SAP into PA. This study provides a facile and sustainable route for tailoring the performance and functionality of membranes for diverse separation applications.