Erythritol-based polyester loose nanofiltration membrane with fast water transport for efficient dye/salt separation

Loose nanofiltration membranes with a remarkable water permeability are highly promising for the fractionation of dyes and salts in the treatment of textile wastewater. In this study, a novel polyester membrane with unprecedented water permeability was developed via interfacial polymerization (IP), in which meso-erythritol (ME) was utilized as an aqueous monomer. Instead of using toxic catalysts, sodium hydroxide was incorporated to the aqueous solution to catalyze the ester reaction between hydroxyl and acyl chloride. A series of characterizations demonstrated that the formed polyester film is hydrophilic and negatively charged, with microsphere structures on the surface. Due to the low-active hydroxyl groups of the aqueous monomers, the participation of ME could yield a coherent polyester film with slightly loose structure atop the polyethersulfone (PES) membrane. The resultant membrane with high water permeability exhibited both a high rejection of dyes and a high transmission of salts. The rejection of the LNFM-2 membrane with an excellent water permeability of 53.23 LMH bar⁻¹ for Congo red (CR), direct red 23 (DR23), reactive blue 2 (RB2), Na₂SO₄, NaCl was 99.6%, 95.2%, 99.6%, 11.0%, and 5.6% respectively. Furthermore, LNFM-1 has a water permeability of up to 87.13 LMH bar⁻¹ while maintaining a competitive dye/salt separation performance. In addition, this type of polyester membrane has a superior antifouling performance and long-term stability during the filtration of dye/salt mixtures. The newly developed polyester LNF membranes have great application potential in the treatment of textile wastewater. This study paves the way for applying hydroxyl monomers like polyols for constructing TFC membranes for diverse separations.