A highly chlorine-oxidation and fouling resistant thin film nanocomposite membrane enhanced by few-layered graphitic carbon nitride nanosheets

Abstract

In addition to the desalination performance, the importance of chlorine-oxidation and fouling resistance of nanofiltration membranes has also been highly recognized recently for special separation. In this study, the beneficial effects of incorporation of few-layered graphitic carbon nitride (g-C₃N₄) nanosheets on the permeability, chlorine-oxidation and fouling resistance of the polyamide (PA) skin layer were systematically investigated. Overall, the incorporation of single or few-layered g-C₃N₄ nanosheets induced the nodule structures of the thin film nanocomposite (TFN) membrane, which caused a rougher, more hydrophilic, and more stable PA skin layer with greater negative charge. The obtained membranes with 0.0100 wt% g-C₃N₄ nanosheets showed an outstanding water flux of 51.0 L m⁻² h⁻¹, with a high salt rejection with a sequence of Na₂SO₄ > MgSO₄ > MgCl₂ > NaCl. More importantly, the normalized flux of the obtained membrane could reach 0.88 after 450 min of fouling test. Furthermore, the membrane had a normalized salt rejection of 0.99 under 10 000 ppm h chlorination condition. Such an outstanding performance should be ascribed to the enhancement effect of hydrophilicity, the negatively charged surface, and the isolation of free chlorine by g-C₃N₄ nanosheets. Therefore, this study provides a new strategy to improve the overall performance of TFN membranes by the incorporation of 2D nanomaterials, where special attention should be paid to the surface topography of the membranes and the uniform dispersion of 2D nanomaterials.