Positively charged loose nanofiltration membranes via the assembly of amino-quinone networks for efficient dye/salt separation

Nanofiltration (NF) membranes with superior permeability and selectivity are highly desirable for the applications. The development of non-polyamide loose NF membranes with high permeability and dye/salt selectivity has aroused great attention in recent years. In this work, 2-hydroxy-1,4-naphthoquinone, a natural compound commonly existed in plants, was chosen to prepare loose NF membranes via the co-deposition with polyethyleneimine (PEI). By optimizing the deposition conditions, we successfully fabricated amine-quinone network coatings on the surface of polyacrylonitrile (PAN) ultrafiltration membranes, and further cross-linked the coatings with glutaraldehyde to improve the compactness and stability. For this kind of loose NF membrane, the rejections to dyes with a molecular weight larger than 600 Da reach 98 %, and the water permeance keeps above 10 L·m−2·h−1·bar−1. In contrast, the rejections to inorganic salts (NaCl, Na2SO4, MgCl2, and MgSO4) are only about 10 %, and the selectivity of the dye molecule alcian blue against NaCl can reach 430. These results prove that this novel composite membrane can realize effective separation for dyes with different molecular weights and desalination for dye solutions. The present work will open up an avenue for designing loose NF membranes with novel separation layers.