Novel polyfurfuryl alcohol loose nanofiltration membrane for efficient dye/salt selective separation

Loose nanofiltration (LNF) is a novel separation and purification technology to achieve organic wastewater treatment and sustainable recovery and recycling of available components in wastewater. However, it is still a formidable challenge to further improve the selectivity and permeability of LNF membranes in applications. In this study, Polyfurfuryl alcohol (PFA) LNF membranes with controllable pore structure were constructed from furfuryl alcohol (FA) on the surface of poly(ether sulfone) (PES) substrate by an acid-catalyzed in situ self-polymerization approach. By regulating the concentration of FA, the hydrophilicity, pore size distribution, and charge properties of the PES/PFA membranes were optimized to achieve the high flux and selective separation efficient. The results showed that the PES/PFA LNF membrane presented a uniform porous structure and exhibited considerable hydrophilicity and electronegativity. The optimized membrane (PES/PFA-2.0) exhibited excellent water flux (∼112.04 L m^-2 h^-1 bar^-1), high dye rejection (e.g. R_CR > 98 %) and low rejection of salts (R_salts < 15 %). The PES/PFA-2.0 membrane also exhibited a high dye/salt separation efficiency (e.g. CR/Na₂SO₄ selectivity ≈ 107.62). In addition, the PES/PFA-2.0 membrane demonstrated an excellent long-term stability and significant anti-contamination properties due to the rigid cross-linked network of PFA with hydrophilic and electronegativity surface modifications. The acid-catalyzed in situ self-polymerization of FA proposed in this study provides a feasible membrane separation solution for high-salt wastewater treatment and conforms to the demand of sustainable chemical development.