In order to obtain high water flux and salt rejection polyelectrolyte complex nanofiltration membranes (PECNFMs), a novel type of PECNFMs is prepared with the polyethyleneimine (PEI), the sodium alginate (SA) and the carboxymethyl cellulose (CMC) via the in-situ ionic cross-linking method. The chemical compositions, structures, and hydrophilicity of the PECNFMs are characterized by the Fourier transform infrared spectroscopy (FTIR), the field emission scanning electron microscope (FESEM), and the water contact angle (CA), respectively. The effects of the PEI mass ratios, the polyanionic types, the feed inorganic salts, and the operating temperature on the nanofiltration performance of the PECNFMs are investigated. It is shown that the in-situ ionic cross-linking PEI/ SA PECNFMs enjoy a higher water flux as compared to the PEI/CMCs with the some PEI mass ratio, and the surface charge of the PECNFMs could be turned from negative to positive by increasing the PEI mass ratio. With the optimized PEI/SA value of 0.9, a water flux of 13.4 L·m-2·h-1 is obtained with the MgCl2 rejection being maintained at around 94.0% (with 1 g·L-1 aqueous MgCl2 solution at 25℃ and 0.6 MPa). Moreover, with the PEI/SA value of 0.9, the best Na+/Mg2+ selectivity (αMg2+Na+=10.4) is secured. This study provides an approach for fabricating PECNFMs with high water flux and salt rejection via an in-situ ionic cross-linking method and opens new avenues for fabricating high performance nanofiltration membranes.

polyelectrolyte complex  /  nanofiltration  /  in-situ ionic cross-linking  /  water softening