Chelidonic Acid-Regulated Synthesis of Asymmetric Polyamide Nanofiltration Membrane: Mechanisms and Separation Performance

Abstract

pH-regulated nanofiltration (NF) membranes have been used in many scenarios, but it is difficult to mitigate the inherent “permeability-selectivity” trade-off effect without the elaborate selection of acidic additives. In this study, a unique pyrone dicarboxylic acid, chelidonic acid (CHA), is selected as an additive to regulate the synthesis of asymmetric polyamide NF membrane.The asymmetric structure is confirmed by experimental characterization and theoretical simulation, further, its formation mechanism is elucidated from both thermodynamic reactivity and kinetic diffusion coefficient. Compared with the control NF membrane (Con-11.0), the thinner polyamide (PA) layer thickness and the slightly enlarged average pore diameter significantly enhance the permeation flux of NF membranes; compared with HCl-regulated NF membranes, the asymmetric structures (relatively dense upper layer of PA) of the CHA-regulated NF membranes maintain the higher rejections of Na2SO4 (97.2%) and antibiotics (96.1% of erythromycin, 93.6% of ceftazidime, 90.2% of tetracycline). This greatly alleviates the “permeability-rejection” trade-off effect of NF membranes, and can be widely used in antibiotic separation and purification, and other water treatment fields. Moreover, the comparison of three typical carboxylic acids (BA, IPA and TMA) proves the specificality of pyrone structurein regulating the asymmetric NF membranes, and the importance of the structure and true ionization of acidic molecules, and their interactions with amine monomers in the interfacial polymerization regulation. The method of CHA-regulated asymmetric PA layer tactfully provides a new way to develop NF membranes with excellent comprehensive performance.

Keywords: Chelidonic acid (CHA), Asymmetric NF membranes, Thermodynamic reactivity, Kinetic diffusion coefficient, Excellent comprehensive performance