Development of Mixed-Dimensional Membranes Comprising Halloysite Nanotubes and Kevlar Aramid Nanofiber for Enhanced Small-Molecule Dye/Salt Separation

In this work, the novel mixed-dimensional nanofiltration membranes [halloysite nanotubes (HNTs)/Kevlar aramid nanofiber (KANF)] with the ability to separate small-molecule dye/salt mixtures were prepared by comprising the rigid HNTs and the soft KANF. The considerable sieving in separating low-molecule dyes from dye/salt mixture solution was designed via the provision of additional channels for water molecules and salt ion transport via the special structure of the hollow structure of HNTs. The optimal 30% HNTs/KANF membrane displayed an eightfold water flux (39.2 L m–2 h–1) of the HNTs-free membrane, the low rejection of salts (21.7% for Na2SO4 and 7.7% for NaCl), and high rejection of various dyes (98.7% for Coomassie brilliant blue G-250, 95.3% for Congo red, 99.5% for Eriochrome black T, and 98.0% for Tropaeolin O). Besides, owing to the hydrophilicity of HNTs and the highly ordered and compact structure of KANF, the HNTs/KANF mixed-dimensional membrane showed excellent antipollution performance and long-term stability. This study provides some ideas for improving the permeability and selectivity of nanofiltration membranes by adding nanomaterials with special structures.