Ionic liquid grafted polyamide 6 as porous membrane materials: Enhanced water flux and heavy metal adsorption

The design and preparation of new membrane material are of great importance. In this work, a hydrophilic ionic liquid (IL) grafted polyamide 6 (PA6) (IL-g-PA6) porous membrane materials were designed and prepared via radiation induced grafting method. The improved hydrophilicity, solubility and the unique ion structure of IL-g-PA6 made it suitable to prepare porous membrane using simple immersion precipitation phase inversion method. SEM images showed opened sponge-like pores for both PA6 and IL-g-PA6 porous membranes, while the pore size decreased and porosity increased as ionic liquid was grafted on PA6. It is believed that the mass transfer process was slowed down by enhanced hydrophilicity and solubility of IL-g-PA6, which lead to a different porous structure from that of PA6. Besides, even though the pore size of 2%-50 K membrane was much smaller, the water flux of which was 2.6 times higher than that of PA6 membrane. Moreover, the chromate sorption on 8%-50 K membrane was 2.7 times higher than that of PA6 membrane, which implies that the IL-g-PA6 porous membranes are good sorbent for heavy metal ions. The special interaction between grafted ionic liquid and heavy metal ions would account for the excellent adsorption property.