Enhanced Polyimide–Graphene Oxide Nanofiltration Membranes for High-Efficiency Separations of Inorganic Salts and Organic Dyes

Polyimide (PI) nanofiltration (NF) membranes have garnered significant attention in water purification due to superior separation efficiency and stability. This study presents the fabrication of PI/graphene oxide (GO) NF membranes through a non-solvent-induced phase inversion process, specifically for the separations of inorganic salts and organic dyes. The chemical structures of the PI-GO NF membranes are characterized using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and their properties are examined through zeta potential measurements, water contact angle tests, and thermogravimetric analysis. The incorporation of GO significantly enhances the hydrophilicity of the membranes, subsequently optimizing their separation capabilities. Filtration experiments demonstrate that the addition of GO notably increases the water permeance of the PI NF membranes and substantially rejects negatively charged organic dyes such as Coomassie Brilliant Blue (CBB), Congo Red (CR), and Direct Black 38 (DB38). Moreover, the PI-GO NF membranes exhibit excellent permeance to inorganic salt ions while effectively removing negatively charged organic dyes. Notably, the membranes also display remarkable separation performance with hot (50°C and 90°C) CBB/Na₂SO₄ feed solutions, indicating their robust thermal stability. These findings suggest that PI-GO membranes hold substantial promise in the field of separation technology, owing to their exceptional permeance and separation performance.