Tris-phenol phosphine oxide-based polyester loose nanofiltration membranes with a three-dimensional structure for efficient dye/salt separation

Abstract

Loose nanofiltration (LNF) membranes prepared by hydroxyl monomers with good dye rejection and inorganic salt permeation properties have attracted significant attention for treating salt-containing textile wastewater. This study adopted interfacial polymerization (IP) method to fabricate a novel polyester LNF membrane, in which tris (4-hydroxyphenyl) phosphine oxide (THPPO) with a steric structure was employed as the solely aqueous monomer. To enhance the solubility and esterification reaction activity of THPPO, sodium hydroxide (NaOH) was specially adopted in aqueous phase, helping the development of the polyester selective layer. The findings demonstrated that the prepared ultrathin (30–38 nm) polyester selective layer exhibited a smooth surface with a negative charge. The optimal membrane LNF-0.05 exhibited a good water permeance of 20.8 L m⁻² h⁻¹ bar⁻¹, excellent rejection of anionic dyes (99.6 % for EBT, 99.3 % for CR, 98.8 % for DR 23, and 98.1 % for MB), and low rejection of monovalent salts (8.2 % for NaCl, 5.0 % for MgCl₂), showing excellent EBT/NaCl mixture selectivity as high as 221. The performance stability of the membranes was partially testified by continuous filtration process. These results confirm the significant application potential of tris-phenol phosphine oxide-based polyester LNF membrane for treating saline textile wastewater.