Membranes with negatively-charged nanochannels fabricated from aqueous sulfonated polysulfone nanoparticles for enhancing the rejection of divalent anions

Nanofiltration membranes (NFMs) with negatively-charged nanochannels (NCNs) are of critical significance for enhancing the rejection of divalent anions. Herein, NFMs with NCNs are fabricated through a facile coating-heating route. Sulfonated polysulfone (SPSF) nanoparticles (13–40 nm) dispersed in aqueous phase are used to generate a dense layer on PES ultrafiltration (UF) membranes with different molecular weight cut-off (MWCO). It is found that the differences in the roughness of the substrates have significant contributions to the packing process of the SPSF nanoparticles, which indicate the smooth surface can be the better one. Scanning electron microscopy (SEM) images suggest the successful fabrication of the dense layer about 200 nm on different substrates. The resultant membranes feature selective layers with the nanochannels from 0.7 to 1.2 nm in average and zeta potential measurements indicate the nanochannel layers are negatively charged, causing the salts rejection in the following sequence: Na 2 SO 4  > NaCl > MgSO 4  > MgCl 2 . Furthermore, the constructed membranes exhibit an excellent separation performance with the water flux of 7.2 L m −2  h −1 bar −1 and the rejection rate for Na 2 SO 4 of 94%, which demonstrates a novel economic and effective approach towards fabrication of nanofiltration membranes.