Macrocyclic pillararene-based polyester loose nanofiltration membranes for efficient dye/salt separation

Abstract

Loose nanofiltration membranes, particularly those fabricated using hydroxyl-based monomers, have garnered considerable interest due to their exceptional ability to reject dyes while allowing the passage of monovalent salts. These properties make them highly suitable for applications in resource recovery and the treatment of saline textile wastewater. In this study, a series of well-designed macrocyclic polyester loose nanofiltration membranes were fabricated through classic interfacial polymerization, involving the reaction of an aqueous monomer containing pillar[n]arenes with their intrinsic cavity structure and an organic phase containing 1,3,5-benzenetricarboxylic acid chloride. Notably, triethylamine was employed as an acid-binding agent to enhance the solubility and esterification reactivity of P[n], facilitating the formation of an ultrathin polyester selective layer (56–85 nm). The macrocyclic pillar[n]arene-based polyester loose nanofiltration membranes exhibited a smooth, negatively charged surface and achieved a high water permeance of 89.35 L m⁻² h⁻¹ bar⁻¹, good dye rejection (97.92 % for Congo red, 95.27 % for Methyl blue), and low rejection of inorganic salts (4.3 % for NaCl, 3.5 % for MgCl₂). Remarkably, the Congo red/NaCl mixture selectivity reached 46.0. These macrocyclic loose nanofiltration membranes showed stable performance during continuous filtration, confirming the significant potential of macrocyclic pillar[n]arene-based polyester loose nanofiltration membranes for treating salt-containing textile wastewater.