Facile fabrication of graphitic carbon nitride nanosheets and its integrated polyamide hyper-cross-linked TFC nanofiltration membrane with intrinsic molecular porosity for salts and organic pollutant rejection from water

A new intrinsically and molecularly porous highly dense hyper-cross-linked polyamide thin film composite nanofiltration membrane was fabricated by incorporating graphitic carbon nitride (g-C₃N₄) nanosheets in the polyamide (PA) active layer through interfacial polymerization on the surface of ultrafiltration PSf/PET support (fabricated by phase inversion). The g-C₃N₄ nanosheets were fabricated through thermal pyrolysis and homogenously dispersed in an aqueous solution of a linear aliphatic tetra-amine prior to interfacial polymerization with non-aqueous solution of terephthaloyl chloride (TPC) and the fabricated membrane was named as g-C₃N₄/PA@PSf/PET membrane. The g-C₃N₄ nanosheets and g-C₃N₄/PA@PSf/PET membrane were thoroughly characterized by TEM, FE-SEM, FT-IR, Water contact angle (WCA), elemental mapping and EDX analysis. FE-SEM of the g-C₃N₄/PA@PSf/PET membrane showed uniform and equal distribution of g-C₃N₄ nanosheets in the polyamide active layer. In the crossflow nanofiltration performance test, the membrane showed a water flux of 55.71 L m⁻²h⁻¹ and % rejection of >85% of MgSO₄ while the % rejection of Eriochrome Black T reached to >99.5% leading to clean and potable water as a permeate. The % rejection of membrane followed the following trend of % rejection as MgSO₄ > MgCl₂ > Na₂SO₄ > CaCl₂ > NaCl. This study shows that the incorporation of g-C₃N₄ nanosheets is an excellent option for enhancing the nanofiltration performance of the membranes.