Covalent organic frameworks (COFs), which are constructed from organic linkers, are a new class of crystalline porous materials comprising periodically extended and covalently bound network structures. The intrinsic structures and the tailorable organic linkers endow COFs with a low density, large surface area, tunable pore size and structure, and facilely-tailored functionality, attracting increasing interests in different fields including membrane separations. Exciting research activities ranging from fabrication strategies to separation applications of COF-based membranes have appeared. This review analyzes the synthesis and applications of diverse continuous/discontinuous COF membranes, such as COF-based mixed matrix membranes (MMMs), COF-based thin film nanocomposite (TFN) membranes, and free-standing COF films. Special attention was given to pore size, stability, hydrophilicity/hydrophobicity and surface charge of COFs in view of determining proper COFs for membrane fabrication, along with the approaches to fabricate COF-based membranes, such as blending, in situ growth, layer-by-layer stacking and interfacial polymerization (IP). Moreover, applications of COF-based membranes in gas separation, water treatment (deaslination and dye removal), organic solvent nanofiltration (OSN), pervaporation and fuel cell are disscussed. Finally, we illustrate the advantages and disadvantages of COF-based membranes through a comparison with MOF-based membranes, and the remaining challenges and future opportunities in this field.

The development of super-hydrophobic surfaces for water/oil separation has attracted much interest in fundamental research and industrial applications in recent years. This article proposes a facile method to fabricate super-hydrophobic surfaces on 3D printed polysulfone (PSU) membranes via the coating of candle soot. A 3D printed PSU membrane fabricated by selective laser sintering was applied for the oil/water separation and showed a different wettability on its top surface and bottom surface. The self-assembled candle soot loose network endowed the 3D printed PSU membrane with super-hydrophobicity with a water contact angle of 161° and a sliding angle of 5°, preserving an outstanding mechanical stability under sonication and chemical stability in 1 M HCl, 1 M NaOH, 1 M NaCl and hot water. Interestingly, this super-hydrophobic surface could dramatically switch to a super-oleophobic state after being prewetted by water. Ten cycles of switchable oil/water separation were performed, demonstrating a high oil/water separation stability of the dry candle soot coated PSU membrane and the water prewetted candle soot coated PSU membrane. Additionally, the effect of selective laser sintering processing parameters on the structure and performance and the influence of the immersion time on the deposition of candle soot were investigated. Overall, this study provides an efficient, simple and reliable fabrication method for super-hydrophobic surfaces with switchable wettability.