Nanofoaming by surfactant tunes morphology and performance of polyamide nanofiltration membrane

Fabricating nanofiltration (NF) membrane with a crumpled structure is promising for improving water permeance without compromising selectivity. Nanobubbles, which are in-situ produced during the interfacial polymerization (IP) of m-phenylenediamine (MPD)/trimesoyl chloride (TMC) system, enabled templating the “ridge-and-valley” structure of thin-film composite (TFC) reverse osmosis (RO) polyamide (PA) membranes. However, the templating effect of nanobubbles in NF PA membrane fabrication is rarely aware in the literature. Herein, we used a surfactant [sodium dodecylbenzene sulfonate (SDBS)] for reducing the interfacial tension and foaming, which enabled introducing additional nanobubbles into the piperazine (PIP)/TMC system. This would ensure that there are adequate amounts of nanobubbles to shape the PA structure, facilitating the encapsulation of nanobubbles between the PA layer and the substrate to form a bubble-like crumpled structure. The bubble-like crumpled structure increased the specific surface area and nanovoids of PA layer, beneficial for the improvement of membrane water permeance. In the presence of SDBS, the elimination of nanobubbles could change the crumpled structure to a smooth surface, while the enhancement of nanobubbles enabled more intensified crumpled structures. Our study provided a new dimension to manipulate the nanoscale structure of the PA layer of TFC NF membranes.