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Effective fractionation of dyes and salts (NaCl) potentially paves a new path to sustainable treatment of textile wastewater. Herein, a loose nanofiltration (NF) membrane was innovatively used as the anion conductive membrane in electrodialysis (ED) for dye and salt separation. The NF membrane with a molecular weight cut-off of 678 Da showed a sufficient retention for reactive dyes with small molecular weights (<627 Da) predominantly based on synergistic effect of steric repulsion and Donnan repulsion. Simultaneously, the NF membrane had a considerably fast transport for anions (i.e., Cl−), as its loose surface structure created extra nano-channels for ion transfer. The anion conductive loose NF membrane based ED process yielded excellent separation performance in a one-step dye/NaCl fractionation. Specifically, a 98.9% desalination efficiency was obtained by the loose NF-based ED process along with 99.4% dye recovery. Additionally, an extremely low fouling propensity was observed during a 5-cycle ED operation, as the negative surface charge of the loose NF membrane served as an intrinsic barrier to prevent the dye species from entering the membrane pores through electrostatic repulsion. This study demonstrated a desirable potential of loose NF membranes as anion conductive membranes in ED for resource recovery from highly-saline wastewater. Image 1 1. Loose nanofiltration (NF)-based electrodialysis (ED) was used for dye/salt separation 2. Loose NF membrane shows an excellent ion transport as anion conductive membrane 3. Loose NF-based ED yields 98.9% desalination efficiency and 99.4% dye recovery 4. Low fouling propensity is observed for loose NF membrane as anion conductive membrane [ABSTRACT FROM AUTHOR]

The growing concern over heavy metal ion contamination in industrial wastewater, posing a significant threat to global public health, has led to a heightened interest in devising efficient removal methods. Nanofiltration, while promising, faces a substantial challenge in simultaneously achieving a high rejection of heavy metal cations and maintaining an elevated water permeance. In response, this study utilizes a simple approach by employing choline chloride with a quaternary ammonium group to modify the surface of PEI-TMC membrane, leading to the design of a high-performance PEI-TMC-CC membrane. The choline chloride modification optimized the surface morphology, hydrophilicity, roughness, and combined the Donnan exclusion effect as well as sieving effect, enabling the PEI-TMC-CC membrane to achieve an exceptional rejection of heavy metal ions while retaining a great water permeance. An impressive water permeance 10.0 L m−2 h−1 bar−1 was performed by the PEI-TMC-CC membrane, nearly three times that of traditional PEI-TMC membranes. Concurrently, the PEI-TMC-CC membrane demonstrated an impressive rejection of heavy metals Cd2+, Pb2+, Ni2+, Zn2+, and Cu2+, reaching rejections of 98.3 %, 95.9 %, 98.1 %, 98.5 % and 99.1 %, respectively. Moreover, density functional theory (DFT) calculations confirmed the improved hydrophilicity of choline chloride molecules, aligning with experimental results. The modification of traditional nanofiltration membranes using cost-effective, hydrophilic, positively charged chemicals not only leads to significant performance improvements but also holds the potential to advance the development of positively charged nanofiltration membranes tailored for the removing of heavy metals cations from wastewater. This approach demonstrates promising prospects for industrial applications and further development. [Display omitted] • The affordability and non-toxic choline chloride was employed to modify the surface of PEI-TMC membrane. • The hydrophilicity of choline chloride were demonsitrated by Density Functional Theory method. • The choline chloride improve the membrane permeance while retaining the great rejection of heavy metal cations. [ABSTRACT FROM AUTHOR]