COF-based nanofiltration membrane for effective treatment of wastewater containing pharmaceutical residues

Nanofiltration has been identified as an effective method for removing emerging pharmaceuticals from wastewater with potential to mitigate environmental impacts and improve water quality. However, the low separation efficiency from the current nanofiltration membranes impeded their development. Here, using the vacuum-assisted self-assembly method, we prepared a thin film composite membrane by stacking covalent organic framework (COF) nanosheets on a predesigned ceramic hollow fibre. By adding methanol as the co-solvent for the assembly, a continuous and defect-free COF TpPa-SO3H layer was formed on top of the YSZ hollow fibre. The resultant COF composite membrane showed high rejection for five environmentally persistent pharmaceuticals (i.e., diclofenac, sulfamethoxazole, ketoprofen, naproxen, and ibuprofen). The hydrophilic pore surface and strong keto-amine linkages of the COF ensured high and stable permeation during operation with separation governed by electrostatic repulsion and steric exclusion. Due to our design using ceramic hollow fibres, these membranes have a small footprint and can be easily integrated into existing water treatment systems. These features make COF-based nanofiltration membranes a promising option for mitigating the environmental impacts of emerging pharmaceuticals in wastewater.