Ordered crown-ether 2D framework based loose nanofiltration membranes for improved separation and stability

Abstract

Loose nanofiltration (LNF) membranes, known for high water permeability and dye/salt selectivity, have been widely used. However, LNF membranes fabricated through layer-by-layer (LbL) assembly lack structural stability and uniformity. Herein, we employed a 2D crown-ether framework (C₂O) for LbL assembly due to its physical stability, uniform pores, and chemical robustness. The LbL membrane exhibited a high water permeance of 39 L m⁻² h⁻¹ bar⁻¹, excellent dye rejection of 99.8% for methyl blue (MB) and congo red (CR), and 99.7% for eriochrome black T (EBT), as well as superior dye/salt selectivity (EBT/NaCl selectivity of 295). Furthermore, the membrane showed remarkable stability under varying pH conditions and throughout prolonged operation.