Defect-engineered metal organic framework thin film nanocomposite membranes for enhanced forward osmosis performance...

The integration of metal-organic frameworks (MOFs) into forward osmosis (FO) membranes has emerged as an effective approach to improve water permeability while mitigating persistent challenges such as high reverse salt flux (RSF) and fouling. In this study, a novel defect-engineered UiO-66-NH₂ was synthesised and integrated into the polyamide (PA) selective layer of thin-film nanocomposite (TFN) FO membranes. Structural defects in UiO-66-NH₂ were introduced using citric acid-crosslinked chitosan (CSC) as a biopolymer modulator, which simultaneously enhanced the porosity of the MOF structures as well as their interfacial compatibility with the membranes and their hydrophilicity. The TFN membranes were prepared via interfacial polymerisation and systematically evaluated for water flux, RSF, surface properties, and fouling behaviour. The optimised TFN membrane containing 0.1 wt% defective UiO-66-NH₂/CSC exhibited a three-fold increase in the water flux and a 43 ± 7% reduction in the RSF compared to the control PA membrane. In addition, it outperformed the TFN membrane incorporated with 0.1 wt% non-defective UiO-66-NH₂, achieving a further 20 ± 3% enhancement in water flux and a 10 ± 2% reduction in RSF. These improvements are attributed to defect-mediated water transport pathways, enhanced surface hydrophilicity, and improved MOF-polymer interactions that promote a more uniform and selective PA layer. Moreover, the defective UiO-66-NH₂/CSC TFN membrane demonstrated superior resistance to microplastic (MP) fouling, with a smaller flux reduction (3%) and maintaining >95% flux recovery after physical cleaning. These findings highlight the potential of defect-engineered MOFs using green polymers in developing high-performance FO membranes for advanced water treatment applications.