pH-regulated interfacially polymerized nanofiltration membranes to achieve high separation of NOM and moderate desalination for purifying ground water

Highly permeable nanofiltration (NF) membranes with efficient natural organic matter (NOM) removal yet preserving essential minerals are of great significance for purifying ground water. In this work, a novel pH-regulated interfacial polymerization (PRIP) strategy was proposed to fabricate ultra-low pressure NF membranes. This strategy was achieved by changing the aqueous solution pH (5, 7, 9, and 11) during IP process. The effects of pH-regulated processes on the structure, chargeability, and physicochemical properties of NF membranes were systematically investigated. Tailored NF membranes under acidic conditions (TFC-pH 5) achieved the ultrahigh permeability of 42.9 L m−2 h−1 bar−1 and 83.3 % moderate rejection of Na2SO4. For the NF membranes prepared under alkaline conditions (TFC-pH 11), the sieving capacity was obviously improved with fewer defects, and 99.4 % rejection of Na2SO4 was observed. In addition, the purification performance of NF membranes in ground water treatment was further studied. Modified NF membranes showed significant removal of NOM and retain moderate amounts of mineral salts. Finally, the mechanism of the pH-regulated influence on the polyamide active layer formation process was proposed. This study provides a feasible and facile design idea for ultralow-pressure NF membranes in purifying ground water.