Modulating interfacial polymerization via 1-methylimidazole as reactive additive for nanofiltration membrane with high-performance

Abstract

Nanofiltration (NF) membrane technology has become the most critical alternative to resolve fresh water resources shortage and water pollution. Preparing polyamide (PA) NF membrane with excellent water permeance and mono/multivalent salts selectivity is highly desired. Herein, we introduced 1-methylimidazole (1-MI) as a reactive additive into interfacial polymerization (IP) to prepare NF membrane and attempted to improve the NF membrane performance. 1-MI modified NF membranes exhibited enlarged pore size and thickness of PA layer, as well as a smooth and hydrophilic membrane surface, the water permeance improved from 7.7 L/(m²·h·bar) of Virgin-NF to 13.1 L/(m²·h·bar) of 1-MI-0.05-NF. The Na₂SO₄ rejection was maintained at 95.01% while NaCl rejection dramatically reduced from 25.79% to 13.29%, and the Cl⁻/SO₄²⁻ selectivity slightly increased from 21.47 to 23 under the mixed salts solution as feed. The enhancement of water permeance was ascribed to the looser PA layer and enhanced hydrophilicity. The retaining Na₂SO₄ rejection was attributed to electrostatic repulsion caused by more carboxylic acid groups, and the decreased NaCl rejection was ascribed to the looser PA layer. Besides, the modified membrane had an acceptable pH stability. In summary, 1-MI modified NF membrane was suitable for the separation of monovalent/divalent anionic salts.