Interfacial construction of PIM-based interlayers in nanofiltration membranes for efficient saline wastewater treatment

Abstract

The coexistence of inorganic salts and organic micropollutants, such as dyes and antibiotics, in saline wastewater presents a significant challenge for effective water treatment. Nanofiltration (NF) membranes have emerged as a promising technology for the simultaneous removal of these pollutants. However, the performance is often constrained by the intrinsic trade-off between permeability and selectivity. To address this limitation, polymers of intrinsic microporosity (PIMs) were introduced as an interlayer to modulate the interfacial polymerization process, resulting in the formation of a highly crosslinked and wrinkled selective layer (∼12 nm) that significantly enhanced both permeability and molecular selectivity. The optimized NF membrane exhibited a remarkable increase in water flux (24.2 L m⁻² h⁻¹·bar⁻¹) compared to the pristine membrane (13.8 L m⁻² h⁻¹·bar⁻¹), while maintaining a high Na₂SO₄ rejection rate (>98.5 %). To elucidate the formation mechanism of the selective layer, dansyl chloride was employed as a fluorescent probe, enabling visualization of monomer adsorption during interfacial polymerization. Molecular simulations further revealed that the PIM interlayer enhanced piperazine adsorption at the interface while restricting its diffusion into the organic phase. In addition, the membrane demonstrated excellent antifouling performance, long-term operational stability, and superior ion separation, achieving a Cl⁻/SO₄²⁻ selectivity of 71.7, six times higher than the commercial NF membrane. Outstanding separation was also achieved in dye/salt and antibiotic/salt systems, with separation factors exceeding 240.0 for Congo Red/NaCl. This study provides valuable insights into the rational design of NF membranes with enhanced permeability and selectivity, offering a promising strategy for the efficient removal for inorganic salts and organic pollutant in advanced water treatment applications.