Zirconiumv (IV)-carboxylate metal-organic framework (MOF) UiO-66 nanoparticles were successfully synthesized and incorporated in the polyamide (PA) selective layer to fabricate novel thin-film nanocomposite (TFN) membranes. Compared to unmodified pure polyamide thin-film composite (TFC) membranes, the incorporation of UiO-66 nanoparticles significantly changes the membrane morphology and chemistry, leading to an improvement of intrinsic separation properties due to the molecular sieving and superhydrophilic nature of UiO-66 particles. The best performing TFN-U2 (0.1 wt % particle loading) membrane not only shows a 52% increase of water permeability but also maintains salt rejection levels (∼95%) similar to the benchmark. The effects of UiO-66 loading on the forward osmosis (FO) performance were also investigated. Incorporation of 0.1 wt % UiO-66 produced a maximum water flux increase of 40% and 25% over the TFC control under PRO and FO modes, when 1 M NaCl was used as the draw solution against deionized water feed. Meanwhile, solute reverse flux was maintained at a relatively low level. In addition, TFN-U2 membrane displayed a relatively linear increase in FO water flux with increasing NaCl concentration up to 2.0 M, suggesting a slightly reduced internal concentration polarization effect. To our best knowledge, the current study is the first to consider implementation of Zr-MOFs (UiO-66) onto TFN-FO membranes.

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Forward osmosis (FO) is an emerging technology for environmental applications such as seawater desalination and wastewater treatment. However, the lack of long-term water stability and internal concentration polarization (ICP) phenomenon of FO membranes are the key challenges limiting its impact in real practice. In this study, we explore the use of water-stable metal−organic framework UiO-66 in different concentrations as fillers for the fabrication of high-performance and water-stable FO mixed-matrix membranes (MMMs) with mitigated ICP. The influences of UiO-66 on the phase inversion pathway and postinterfacial polymerization reaction cause changes in membrane morphology and chemistry, reducing the membrane structural parameter (S) and mitigating the ICP effect. As a result, the best performing FO membrane (6.5 wt % UiO-66) exhibits a 50% increased water flux over the pristine membrane, when deionized water and 1 M NaCl are used as the feed and draw solutions, respectively. The extent of ICP mitigation has been quantified by the solution-diffusion model, demonstrating effective control by the presence of UiO-66. Because of the excellent water stability of UiO-66, no significant degradation of water permeability is observed over 72 h operation. Therefore, the newly designed UiO-66 incorporated FO MMMs are of great interest and have potential for advancing membrane performances in water filtration and related environmental practice.

For the first time, continuous polycrystalline UiO-66−NH 2 thin film supported by a cross-linked Matrimid substrate was successfully fabricated via in situ solvothermal synthesis at room temperature for organic solvent nanofiltration. The integrated structure of the formed UiO-66− NH 2 selective layer was inferred by various characterizations including X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. We have demonstrated that pretreatment of the substrate by an organic ligand, the number of solvothermal synthesis cycles, and the reaction time play important roles in MOF film formation. The newly developed UiO-66−NH 2 membrane possesses high surface hydrophobicity and mean pore size of 0.89 nm in diameter. It shows an exceptional rejection of 96.33% to Rose Bengal with moderate ethanol permeance of 0.88 L m −2 h −1 bar −1 . Benefiting from the extraordinary chemical stability of Zr-MOF crystals, the UiO-66−NH 2 membrane shows excellent stability in different solvents, implying their great potential for real applications. This work provides useful insights into the fabrication of continuous UiO-66-type MOF membranes on polymeric substrates, which are very promising in practical separations involving organic solvents.

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