A review on recent advances in covalent organic frameworks-based membranes: Synthesis, modification, and applications in liquid phase separation

The ever-growing global population and the scarcity of clean water resources are major social challenges. In response, researchers are exploring novel materials for water treatment, with a focus on producing high-quality drinkable water for various uses. Covalent organic frameworks (COFs) are a type of porous organic polymers that possess well-defined pore architectures and are constructed through covalent bonds between organic building blocks. COFs offer considerable potential in the field of membrane separation due to their unique characteristics, such as consistent pore sizes, regular pores, and diverse pore environments. In this review paper, we provide an in-depth evaluation of the recent advancements in the synthesis and modification of COF-based membranes, including the fabrication of hybrid COFs, surface modification, and defect engineering for liquid phase separation. Firstly, we discuss conventional COF processing techniques such as support-assisted, free-standing, and mixed matrix membranes (MMM). Secondly, the reactivity of synthesizing monomers is a critical factor in the development of advanced COF-based membranes. Therefore, we emphasize the nature and reactivity of reacting amine and aldehyde monomers and their significant implications for enhancing the properties and performance of COFs membranes. Finally, we highlight the applications of COF membranes in water treatment, organic solvent nanofiltration, desalination, and heavy metal recovery operations. Our comprehensive review aims to provide an essential guide for researchers in the field of liquid phase separation techniques with an interest in developing unique COF membranes for improved water treatment processes.