PH-responsive nanofiltration membranes containing carboxybetaine with tunable ion selectivity for charge-based separations

Abstract

Although multiple methods and materials have been developed to fabricate pH-responsive membranes, separating organics/inorganic salts mixtures and divalent/monovalent ions systems with these membranes still remains a challenging task. In this study, pH-responsive nanofiltration membranes (PCHMs) with tunable ion selectivity were first prepared with poly(carboxybetaine methacrylamide (CBMA) -co-N-(Hydroxymethyl) acrylamide) (PCHs) through surface coating and glutaraldehyde cross-linking method. The membrane ion selectivity towards divalent ions and monovalent ions can be well tuned by adjusting the pH of feeding solution. At pH 3.0, the retention of PCHM3 (CBMA content in PCHs is 48.8mol%) to MgCl2 (92.9%) is much higher than that to NaCl (3.4%). And by adjusting the feed pH value to pH 10.0, the retention to Na2SO4 (91.8%) is much higher than that to NaCl (3.8%). While at neutral environment, PCHM3 allows the transport of the inorganic salts but blocks the transport of PEG800. It indicates that PCHMs could be a kind of high performance membranes for divalent/monovalent ions separation and organics/inorganic salts separation. Furthermore, the PCHMs possess a reversible and stable pH-responsive property, which is essential for practical charge-based separations. The responsiveness and adaptiveness of the PCHMs to the feeding solution make it being a versatile material for custom-designed membrane separations.