Self-assembled MOF membranes with underwater superoleophobicity for oil/water separation

Metal-organic frameworks (MOFs) have attracted extensive attention in catalysis and adsorption fields due to the large surface area and tunable pore structure, however MOFs have not been so broadly exploited for water treatment primarily due to their low water stability and hydrophilicity. In this study, a kind of MOFs, poly(acrylic acid) (PAA) modified UiO-66-NH₂ (UiO-66-NH₂@PAA), was first synthesized and used to fabricate membranes via vacuum-assisted self-assembly process. Owing to the high water adsorption ability of MOF, abundant hydrophilic, negatively-charged carboxyl groups and high surface roughness, the membranes exhibited high hydrophilicity and underwater superoleophobicity, and thus better antifouling performance. Owing to the ionization and deionization ability of carboxyl groups, the membranes exhibited good stability in the pH range from 1 to 11. Owing to the existence of chemical and hydrogen bond interactions, the membranes exhibited improved multicycle stability. Accordingly, the MOF membranes exhibited high separation efficiency for oil/water emulsion (rejection > 99.9%). Under optimum conditions, the pure water flux was 2330 L m⁻² h⁻¹ bar⁻¹ and the flux recovery ratio (FRR) after 3 cycles separation of oil/water emulsion maintained over 80%, manifesting great potential of MOF membranes in oil/water separation.