Synergistic emulsion effect-inspired design of starch nanoparticle-based nanofiltration membranes with nano-Turing structures for enhanced performance

In this paper, inspired by the synergistic emulsion effect, nano-Turing structured nanofiltration (NF) membranes were prepared using negatively charged starch nanoparticles (SNP) and anionic surfactant sodium dodecyl sulfate (SDS). The SNP and SDS at the water–oil interface were utilized to influence the interfacial properties, and through the synergistic effect resulting from the strong electrostatic repulsion between the two, the organic phase was stably dispersed in the form of oil droplets on the water surface in a transient period. By constructing “ring-like” interfacial polymerization (IP) templates, a polyamide (PA) layer with coffee-ring structures on the surface was finally formed. This structure not only increased the effective filtration area for water molecules, but nanovoids underneath optimized the water transport path and enhanced water flux by suppressing the funnel effect. It was further found by adjusting the SNP content that NF membrane with 0.02 % SNP showed the lowest effective thickness of PA layer and the best wettability. Those factors together contributed to high water flux (29.97 L·m −2 ·h −1 ) and good divalent salt rejection (98.88 %). Furthermore, it showed excellent ionic selectivity (162.6) for Cl − /SO 4 2− . This paper deeply explores the formation mechanism of coffee-ring structures by analyzing the water–oil 2D interface, and the discovery provides a new direction for the preparation of PA NF membrane surfaces with regular patterns.