Hydrophilic polymers of intrinsic microporosity as water transport nanochannels of highly permeable thin-film nanocomposite membranes used for antibiotic desalination

Abstract

Nanofiltration (NF) membranes with superior perm-selectivity are highly desirable in separation and purification processes. In this work, a highly permeable thin film nanocomposite (TFN) NF membrane containing hydrophilic polymer nanoparticles of intrinsic microporosity (PIM NPs) in polyamide (PA) separation layer is developed for antibiotic desalination. The hydrophilic PIM NPs were synthesized by one-pot polycondensation with hydrophilic β-cyclodextrin (β-CD) as one of building units and used as an additive of aqueous phase in the preparation TFN membranes by interfacial polymerization. Unlike commonly-used inorganic nanomaterials, the β-CD-PIM NPs are well compatible with PA matrix due to their polymer characteristic. Moreover, the hydroxyl groups in β-CD can participate in interfacial polymerization and thus the interfacial defects between β-CD-PIM NPs and PA matrix are effectively eliminated. As a result, the TFN membranes exhibit not only high water permeance (15.3 L m−2 h−1 bar−1), about three times as large as that of the prinstine membrane, but also high divalent salt rejection (RNa2SO4 = 95.1%). It is believed that the interior micropores inside β-CD-PIM NPs play a role of water transport nanochannels and contribute to high water permeance of the membranes. The long-term durability of the membranes are superior due to the chemical bonding between β-CD-PIM NPs and PA matrix. In addition, the TFN membranes were used for antibiotics desalination due to their high rejection towards antibiotics, but low rejection towards sodium chloride. This work offers a new strategy for constructing water transport nanochannels in separation layer to develop high performance TFN NF membranes.