300-Nm-Ultrathin Polyethylene Supporting Layer Boosts Nanofiltration Membrane with Superior Mono-/Divalent Anions Selectivity

Abstract

For a long time, research in nanofiltration (NF) membrane has predominantly focused on the selective layer or the interlayer, often overlooking the supporting layer's critical contributions to membrane fabrication and performance. Our study addresses this gap by adopting an ultrathin hydrophilic ultra-high molecular weight polyethylene (PE) membrane as the supporting layer. Exceptionally thin at approximately 600 nm, this hydrophilic-modified PE membrane exhibits high porosity high mechanical strength, and hydrophilic homogeneity in the plane. This innovation not only reduces overall mass transfer resistance, leading to higher flux rates compared to conventional substrates but also allows for more precise control over the formation of the selective layer. This is achieved as the freestanding ultrathin PE membrane serves as a manipulable interface during interfacial polymerization. Consequently, the resulting polyamide layer exhibits a hybrid Turing structure that can be finely modulated. Impressively, our NF membrane demonstrates an ultrahigh Cl-/SO42- selectivity of 338.03, placing it at the forefront of existing literature. The resulting NF membrane boasts an overall thickness of merely ~628 nm, which, to our knowledge, represents the thinnest NF membrane documented to date. This work provides new insights into the unique significance of the supporting layer during selective layer preparation, offering a new strategy for ultrathin, high-performance membranes for nanofiltration and beyond.

Keywords: Polyethylene, Ultrathin, Polyamide, Nanofiltration, Mono-/divalent selectivity