Engineering Interfacial Structure and Channels of Polyamide Thin-Film Nanocomposite Membranes to Enhance Permselectivity for Water Purification

Polyamide thin-film nanocomposite (TFN) membranes provide a promising pathway to alleviate the trade-off between water permeability and selectivity of conventional thin-film composite (TFC) membranes. However, the fabrication of defect-free TFN membranes with enhanced permselectivity remains a challenge due to the formation of defects at the polyamide–filler interface and from filler agglomeration. In this study, a facile interfacial modification strategy was demonstrated to effectively mitigate particle agglomeration and enhance the interaction between the polyamide with the filler particles using UiO-66-NH₂ nanoparticles as the probe fillers, leading to the formation of TFN membranes with excellent interfacial compatibility and selectivity toward both salt ions and small neutral molecules. The TFN membrane with an optimized particle loading shows high rejections of 97.0–99.2% to NaCl, MgCl₂, Na₂SO₄, and MgSO₄ with a water flux greater than 4.0 L m^–2 h^–1 at a relatively low pressure of 150 psi, which represents a ≥23.0% increase in salt rejections relative to the TFC benchmark. Additionally, the TFN membranes show great potential for effectively discriminating small neutral contaminants such as boric acid (H₃BO₃) at a pH value of 7.5, outperforming the commercial TFC membrane benchmark at the same testing conditions. The structural stability of the TFN membranes was confirmed by performing a continuous performance test of 480 h. These findings demonstrate that enhanced size screening for various species can be achieved by TFN membranes based on the engineered interfacial structure of the porous fillers, and the reported method represents an advancement in addressing permselectivity limitations in classic TFNs through a multifaceted yet generalizable approach of reducing particle agglomeration and creating compatible polymer–filler interfaces. We believe this strategy can be applied broadly with different filler systems, enabling TFNs to address a wide variety of unmet separation needs.