Novel poly(ester amide) nanofiltration membranes fabricated utilizing 4-hydroxypiperidine as a co-reactive monomer for monovalent/divalent anionic salt separation

Abstract

The thin-film composite (TFC) nanofiltration (NF) membranes are extremely promising in the field of monovalent/divalent anionic salt separation. The selection of monomers with different reactive groups could enable the TFC NF membranes to be more suitable for monovalent/divalent anionic salt separation. In this study, a novel low-cost compound 4-hydroxypiperidine (HDP) was first utilized with piperazine (PIP) as an aqueous phase co-reactive monomer to fabricate poly (ester amide) (PEA) TFC NF membranes via interfacial polymerization. The addition of HDP made the PEA layer thinner, smoother, and more hydrophilic while also creating larger pores and increasing the surface negative charge density. The water permeance of the optimal membrane NF–1P1H (with a PIP: HDP ratio of 1:1) was 13.67 L·m⁻²·h⁻¹·bar⁻¹, which was 70.24 % higher than that of NF–P (with a PIP: HDP ratio of 1:0). The NaCl/Na₂SO₄ separation factor of NF–1P1H was 43.00, which was 73.39 % higher than that of NF–P. NF–1P1H also had excellent selectivity in the mixed salt solution. In addition, NF–1P1H demonstrated superior operational stability, anti-fouling performance, chlorine resistance, and sufficient pH stability after short-term acid-base immersion. Moreover, the water permeance of NF–1P2H (with a PIP: HDP ratio of 1:2) could reach 15.08L·m⁻²·h⁻¹·bar⁻¹, which was 87.80 % higher than that of NF–P, and its separation factor was maintained at 27.12. This study presents a straightforward and efficient method for fabricating PEA TFC NF membranes with desirable water permeance and monovalent/divalent anionic salt separation performance.