Boric acid-loosened polyvinyl alcohol/glutaraldehyde membrane with high flux and selectivity for monovalent/divalent salt separation

Polyvinyl alcohol (PVA) has the advantages of excellent hydrophilicity, good film-forming properties and competitive prices, thus it is an ideal membrane material. However, rare reports about PVA membrane for monovalent/divalent salt separation, which is widespread in chemical industry can be found. Herein, we developed a novel boric acid (BA)-loosened PVA/glutaraldehyde (GA) membrane with high flux and selectivity for monovalent/divalent salt separation. Our idea is based on the fact that BA and PVA can form a complex due to some special interactions (including chemical bonding and H-bonding). In general, PVA membrane needs to crosslink with GA for obtaining a high salt rejection. However, PVA/GA membrane is usually too compact, leading to a low membrane water flux. The formation of PVA/BA complex reduced PVA/GA membrane crystallinity and increased its pore size, thereby improving the membrane flux obviously (by 16 times). PVA/GA/BA membrane flux is high: under 7.5 bar, its pure water flux was 20.20 L/m2·h. Besides, a high monovalent/divalent salt selectivity (64.21) was also achieved since the rejection of monovalent salt (NaCl) declined sharply and meanwhile the high rejection of divalent salt (Na2SO4) was maintained. Moreover, the developed PVA/GA/BA membrane exhibited a good alkali resistance, antifouling performance and stability of permselectivity, which has a bright application prospect. This work may pave a novel avenue to develop high-performance PVA monovalent/divalent salt separation membranes.