Sub-4 nanometer porous membrane enables highly efficient electrodialytic fractionation of dyes and inorganic salts.

During the synthesis of dyes, desalination of high-salinity dye-containing waste liquor is a critical premise for high-quality, clean dye production. Conventional membrane processes, such as electrodialysis, nanofiltration and ultrafiltration, are inevitably subjected to serious membrane fouling, deteriorating the dye/salt fractionation efficacy. Integrating the technical merits of electrodialysis and pressure-driven membrane separation, we devise an electro-driven filtration process using a tight ultrafiltration membrane as alternative to conventional anion exchange membrane for rapid anion transfer, in view of dye desalination and purification. By employing a sub-4 nanometer tight ultrafiltration membrane as anion conducting membrane, the electro-driven filtration process achieves 98.15% desalination efficiency and 99.66% dye recovery for one-step fractionation of reactive dye and NaCl salt, markedly outperforming the system using commercial anion exchange membranes. Notably, the electro-driven filtration system displays a consistently high and stable fractionation performance for dyes and salts with unprecedentedly low membrane fouling through an eight-cycle continuous operation. Our results demonstrate that the electro-driven filtration process using nanoporous membranes as high-performance anion conducting membranes shows a critical potential in fractionation of organic dyes and inorganic salts, unlocking the proof of concept of nanoporous membranes in electro-driven application.