Deciphering the mechanism insights of carbon nitride mediated thin film nanocomposite membrane towards advanced nanofiltration

Abstract

Recent progress in the membrane field emphasizes the considerable potential of 2D material of carbon nitride (C₂N) as an appealing candidate for new nanofiltration membrane fabrication. In current work, a novel class of thin film nanocomposite (TFN) membrane was developed by embedding the post-synthesized C₂N nanosheets as a quasi-molecular-scale regulator to mediate the interfacial polymerization procedure for achieving high selective nanofiltration. The entrapped heterogenous C₂N nanoflakes disrupt the typical reaction-diffusion proceeding of interfacial polymerization by imparting additional interfacial disturbance and restricting the amine monomer's rapid diffusion towards organic phase, contributing to a thinner polyamide (PA) nanofilm with closely scattered nodes pattern formation on membrane upper surface. Furthermore, the water-harvesting essence of C₂N nanosheets capture amine aqueous micro-phase, assuming the framework of nanofillers and undeviatingly impacting the membrane morphology conversion from flatten to nodes, collaboratively assisting fluid transport pathways creation inside membrane matrix for water molecules quick pass through. Finally, C₂N with porous structure and unshared electron pairs in N atoms interact with water molecules via hydrogen bonding, promoted water easy transport and improved membrane anti-fouling property. Therefore, the best-performing membrane (PA-g-C₂N (0.02)) with augmented separation permeance exhibited intriguing water permeance of 22.18 L m⁻² h⁻¹ bar⁻¹, approximately 3 folds than the pristine PA membrane with comparable salts selectivity (98.61 % for Na₂SO₄ and 60.7 for Cl⁻/SO₄²⁻). Because of the distinctive intrinsic water-affinitive capacity, the PA-g-C₂N (0.02) membrane also displayed superior anti-fouling ability. In general, the as-prepared membrane evinces competitive separation properties compare to that of state-of-the-art desalination membranes and shows good potential in future water remediation.