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/m 2 ·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 (Na 2 SO 4 ) 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 .