Preparation of high-flux loose nanofiltration membranes for efficient dye/salt separation by controlling interface polymerization through physical and chemical dual constraints

Abstract

High-flux loose nanofiltration membranes (LNMs) are ideal for treating and recovering dyes and salts from saline textile wastewater. In this study, a self-synthesized polyphenolic monomer (HCTT) was introduced into an interfacial polymerization (IP) system, establishing a dual physical and chemical constraint mechanism to regulate the reaction rate. Physically, HCTT exhibits a slow diffusion rate and reduces the diffusion rate of piperazine (PIP). Chemically, the phenolic hydroxyl groups of HCTT are less reactive than the amino groups of PIP, enhancing the controllability of the IP process. Using HCTT and anhydrous PIP as the aqueous phase and trimesoylchloride (TMC) as the oil phase, LNMs were prepared on hydrolyzed polyacrylonitrile (HPAN) substrates. The resulting membranes feature a negatively charged hydrophilic surface and a selective layer with a Turing structure, improving water permeability and mass transfer. The membranes achieved a flux of 124.8 LMH bar⁻¹ with dye rejection rates exceeding 95 % for Congo Red (CR) and Methyl Violet (MV) while maintaining low salt rejection rates (14.1 % for Na₂SO₄ and 5.4 % for MgSO₄), resulting in a dye/salt selectivity 14.9 times higher than conventional polyamide membranes. The membranes demonstrated excellent performance in mixed dye/salt solutions and maintained high stability after 48 h of continuous operation, achieving a flux recovery rate of 84.2 % after seven fouling cycles with CR. This study offers a novel and efficient strategy for developing LNMs for dye containing wastewater treatment and resource recovery.