Customizing loose nanofiltration membranes on nanofiber scaffolds with surfactants: Towards efficient dye/salt selective separation

Abstract

A loose nanofiltration membrane prepared using a nanofiber support layer demonstrates significant efficiency and convenience for textile wastewater treatment. However, maintaining high permeability alongside elevated dye/salt selectivity remains a critical challenge. Surfactants, as promising agents for enhancing interfacial tension, can facilitate the preparation of loose nanofiltration membranes (LFNM) by influencing the diffusion rates of amine monomers during the interfacial polymerization process. In this study, sodium dodecylbenzene sulfonate (SDBS) was utilized as a water-phase additive to fabricate nanofiltration membranes of varying thickness on the surface of nanofiber membrane supports. Scanning electron microscopy and atomic force microscopy revealed systematic changes in the morphology of the LFNM, showing a correlation between thickness and surface roughness. Notably, the addition of a small amount of SDBS significantly enhanced membrane permeability and dye/salt selectivity, resulting in LFNMs superior to control membranes. This improvement can be attributed to a more porous polyamide (PA) layer, increased surface hydrophilicity, and a higher molecular weight cutoff. The results indicate that LFNM-0.5 exhibits a high rejection rate for dye (Congo Red) at 98.9% and a low rejection rate for salt (NaCl) at 6.5%. Furthermore, during the selectivity tests on mixed solutions, the dye/salt selectivity of LFNM for Na₂SO₄/CR and NaCl/CR remained stable after 2 h of operation, with the highest selectivity factors reaching 104 and 116.5, respectively. The antifouling and acid-base resistance assessments also demonstrated excellent performance. This suggests that LFNM-0.5 possesses good stability in the dye/salt separation process. This study introduces a novel approach for the preparation of loose nanofiltration membranes by modulating the surfactant strategy for the microscopic structure of the membranes.