Preparation of novel positively charged copolymer membranes for nanofiltration

A novel type of positively charged copolymers, poly (2-methacryloyloxy ethyl trimethylammonium chloride-co-2-hydroxyethyl acrylate) (PDMCHEA) were synthesized via free-radical copolymerization. Positively charged nanofiltration membranes (PCNFMs) were made from PDMCHEAs copolymers via glutaraldehyde (GA) cross-linking method. Chemical structures and compositions of PDMCHEAs and PCNFMs changes with varying copolymerization ratio of DMC to HEA (RDMC/HEA), and were characterized by element analysis, viscosity measurements, attenuated total reflectance fourier transform infrared spectroscopy, field emission scanning electron microscope and atomic force microscopy, respectively. The optimum membrane preparation conditions: 1.5 wt% PDMCHEA, 0.3 wt% GA and cured at 50 °C for 3 h were obtained. Effects of charge density and molecular weight of PDMCHEAs on their membranes’ nanofiltration performance were studied. It was found that the PCNFM3 (RDMC/HEA = 1.28) showed the best salt rejection and water flux, e.g. RMgCl2=94.3%RMgCl2=94.3%, JMgCl2=19.1 L m−2h−1JMgCl2=19.1 L m−2h−1, RNaCl = 60.7% and JNaCl = 20.6 L m−2 h−1, respectively. PCNFM3 exhibited good separating capability and stability in its desalination process. Therefore, PDMCHEA is a promising material for fabricating PCNFMs with high performance in cations separation or recovery.

► Positively charged nanofiltration membranes PCNFMs were prepared with poly (2-methacryloyloxy ethyl trimethylammonium chloride-co-2-hydroxyethyl acrylate) (PDMCHEA) copolymers.
► Nanofiltration performance of PCNFMs changes with varying the charge density and molecular weight of PDMCHEAs copolymers.
► PCNFMs exhibited good separating capability and stability in desalinating multivalent cations.