In situ growth of 2D nanosheets of terbium-based metal organic frameworks as super-hydrophilic and super-oleophobic (underwater) selective layer on a ceramic support for efficient separation of stabilized oil-in-water emulsion

The current study aimed to develop an active layer composed solely of 2-dimensional nanosheets of terbium-based metal organic frameworks (Tb-IPA-NH₂ MOFs) on a ceramic support via an in situ growth approach. The ultimate aim of the current study was to develop a stable, defect-free active layer composed of 2-dimensional nanosheets that can be readily applied under cross-flow filtration conditions for the separation of surfactant-stabilized oil-in-water emulsions. In addition, the current approach for membrane fabrication focuses on reducing the need for high temperatures, high-polarity solvents, and extended growth times for metal-organic frameworks. These purposes were readily achieved by using a higher proportion of the green solvent, ethanol, and a smaller quantity of N,N-dimethylformamide during the in situ growth of 2-dimensional nanosheets on the ceramic support. High-resolution transmission electron microscopy confirmed the thin, sheet-like feature of the 2-dimensional Tb-IPA-NH₂ MOF with an average thickness of 1.8 nm. Moreover, the in situ growth of 2-dimensional Tb-IPA-NH₂ MOFs on a ceramic support yields relatively dense leaf-like growth resembling that of broad-leaved trees that densely populate a forest. As a result, the 2-dimensional Tb-IPA-NH₂ MOF-decorated ceramic membrane exhibited altered surface features, being both superhydrophilic and superoleophobic underwater, with an underwater oil contact angle of 160.7°. The 2-dimensional Tb-IPA-NH₂ MOF-decorated ceramic membrane showed a permeance of 147.9 L m⁻² h⁻¹ bar⁻¹ and a separation efficiency of >99 % using 100 ppm crude oil-in-water emulsion. Moreover, the membrane's separation efficiency remained stable for 660 min. The fouling and cleaning cycles revealed that the majority of the membrane fouling was reversible, as the membrane regained its normalized flux, reaching 0.93 after a decline to 0.20 over 360 min. Hence, the current approach is facile, simple, and yields a continuous layer of 2-dimensional MOFs on a ceramic support, which opens up the route for further tuning the performance of the membrane.