Superhydrophobic fluorinated metal–organic framework (MOF) devices for high-efficiency oil–water separation

Abstract

Oil spills have been a persistent environmental challenge globally, resulting in severe long-term impacts. Thus, developing materials for efficient oil–water separation is crucial. Metal–organic frameworks (MOFs), as a rapidly emerging class of porous materials, have gained tremendous attention due to their ultra-high surface area. In this study, four fluorinated MOFs with UiO-66 topology were synthesized and characterized. Their hydrophobicity was tailored by varying the types and quantities of the fluorine-containing functional groups (–F or –CF₃) on the ligands. Among them, 2CF₃-UiO-66 showed the highest hydrophobicity, with a water contact angle (WCA) of 145.9°, making it promising for adsorbing organic pollutants and as a hydrophobic coating material. 2CF₃-UiO-66 powder efficiently reduced the concentration of 3,5-dichlorophenol (a model halogenated water pollutant) from 300 ppm to 23.4 ppm within 2 hours. Furthermore, 2CF₃-UiO-66 was in situ coated on cotton (CT) and sponge (SP) to form composite materials, 2CF₃-UiO-66@CT and 2CF₃-UiO-66@SP. 2CF₃-UiO-66@CT is superhydrophobic (WCA = 164.7°), flexible, and fire retardant. It efficiently separated water and nine organic solvents via filtration, meeting commercial standards of <0.01% water content in the filtered organic solvents. 2CF₃-UiO-66@CT remains structurally intact after 20 filtration recycles, suggesting its durability. These advantages make the 2CF₃-UiO-66@CT an ideal candidate for oil–water separation via filtration. Alternatively, 2CF₃-UiO-66@SP, with a porous sponge backbone, is suitable for oil–water separation by adsorbing the organic phase efficiently (60–140 g g⁻¹ adsorption capacity on nine organic solvents), and the adsorbed oil can be easily pumped out. Overall, we believe the fluorinated MOFs reported in this work have great potential for adsorption and superhydrophobic coating applications.