Cross-linked g-C3N4 nanofibers enable thermal stable composite membranes for high-performance loose nanofiltration

Abstract

Loose nanofiltration (LNF) membranes show applications in various fields such as the separation of dyes and salts. The development of LNF membranes with high permeability and high dye/salt selectivity has received great attention in recent years. In this study, inorganic graphitic carbon nitride (g-C3N4) nanofibers modified with polyethyleneimine (PEI) were cross-linked by glutaraldehyde to fabricate a novel LNF membrane on polyethersulfone (PES) microfiltration membrane. Owing to the great hydrophilicity, electro-positivity, and unique structure, the composite membrane exhibits excellent Congo red (CR)/NaCl selectivity of 301.8 with water permeance as high as 162.7 L m−2 h−1 bar−1. Moreover, the cross-linked inorganic separation layer enables the membranes with excellent alkali and temperature resistance. After being immersed in an acidic solution (pH = 1) or an alkaline solution (pH = 13) for 48 h, the rejection to CR does not significantly decrease. Furthermore, the nanofiltration membrane maintains structural stability without obvious decline in CR rejections over the temperature range of 25 ∼ 95 °C, demonstrating the potential in high temperature separation. The present work will open up an avenue for designing and fabricating high-performance nanofiltration membranes.