A novel positively charged composite membranes for nanofiltration prepared from poly(2,6-dimethyl-1,4-phenylene oxide) by in situ amines crosslinking

A novel positively charged membrane for nanofiltration was prepared from linear engineering plastics poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by composting the aryl-substitution substrate with brominated polymers of proper benzyl and aryl bromine content (ABC) followed by in situ amine crosslinking. The resultant membrane was characterized with pure water flux and rejection of electrolytes MgCl2 and NaCl. The results show that the membrane nanofiltration properties are significantly affected by the type of brominated polymers of the top layer, the amination time, the composition of amination medium. The pure flux is enhanced by the benzyl substitution of the top layer, amination time, ratio of trimethyl amine (TMA) in amination medium etc.; while the rejection of electrolyte is increased with the aryl substitution of the top layer, ratio of ethylenediamine (EDA) in amination medium, etc. In addition, due to positive charge on the top layer, the membrane behaves much higher rejection for multi-valent cations (e.g. Mg2+) than for monovalent cations (e.g. Na+) if the electrolytes have the same monovalent counterion (e.g. Cl−). Therefore, by properly balancing bromination and amination conditions, a desired positively charged membrane could be obtained for removal of multivalent cations from water or for separation of monovalent cations and multivalent cations.