Interfacial engineering of UiO-66-NH2 nanofillers in TFN membranes for simultaneous salt and boron removal

The fabrication of high-performance desalination membranes capable of removing both ionic species and neutral trace contaminants is critical for advancing seawater desalination. Due to their crystalline nature, tunable porosity, and hybrid inorganic-organic composition, metal-organic frameworks (MOFs) have shown remarkable potential for selective ion removal while maintaining high water recovery. Hence, in this work, we have synthesized nanosized UiO-66-NH 2 to enhance crystal uniformity and reduce defect density during the nanofiller incorporation in the reverse osmosis (RO) membrane. The core of the current study was to explore the optimal strategy for uniformly incorporating this MOF into the polyamide active layer of thin-film nanocomposite (TFN) membranes. Three distinct interfacial polymerization strategies were employed: TFN-A (aqueous-phase dispersion), TFN-O (organic-phase dispersion), and TFN-I (dip-coating on the support layer). Among the fabricated membranes, TFN-A exhibited the highest water flux (up to ~33.8 LMH at 30 ± 1 bar transmembrane pressure) and superior salt rejection (98.8%) under brackish water conditions (2000 mg L −1 NaCl). The TFN-A also exhibits high desalination performance across a range of NaCl and other divalent salt concentrations. The fabricated membrane also shows tremendous performance during long term test for 48 h and improved antifouling properties. Further, the boron rejection tests using 5 mg L −1 boron demonstrate that TFN-A achieves 87.8% rejection in the absence of competing salts and 81.8% rejection in simulated brackish water (2000 mg L −1 NaCl and 5 mg L −1 boron). Furthermore, this study has explored boron rejection at different pH values of the feed, which reveals that boron rejection increases significantly at alkaline pH, reaching 98.1% for TFN-A at pH 13 due to the conversion of boric acid into large borate ions. Hence, the results of the current study highlighted the role of nanosized MOFs in enhancing interfacial compatibility, overall separation performance, and the rejection of challenging neutral species, such as boron, from saline water.