Functionalized g-C3N4 nanosheet interlayer enables enhanced separation performance of nanofiltration membranes

Thin film nanocomposite membrane with a nanomaterial interlayer (TFNi) has attracted extensive attention in recent years. Herein, for the first time, tannic acid (TA) functionalized g-C3N4 nanosheets are used to construct an interlayer for the fabrication of TFNi nanofiltration membranes with enhanced separation performance. The TA-C3N4 nanosheet interlayers possess high hydrophilicity, low resistance for water transport, and strong structural stability, which is conducive to improving water permeance of the TFNi membranes. Meanwhile, the uniformity of interfacial polymerization on the interlayers is improved by virtue of the smooth surface of the interlayer, enabling the formation of an integral and dense polyamide layer with a thickness of only about 10 nm. The TFNi membranes exhibit excellent performance with water permeance of 34.25 L m−2 h−1 bar−1 and Na2SO4 rejection of 98.53%, which are obviously higher than those of the corresponding membrane without TA-C3N4 nanosheets (21.03 L m−2 h−1 bar−1 and 92.04%). The TFNi membranes also show significant selectivity improvement toward divalent/monovalent ions. This work gives inspiration for designing advanced nanofiltration membranes with functionalized nanomaterials acting as interlayers.