Preparation of ionic covalent organic frameworks and their applications in solid-phase extraction

Ionic covalent organic frameworks (iCOFs) possess dual specific properties both COFs and ions, such as tunable cation or anion charge, crystalline structure, large surface area, ordered pore structure, low density, good stability and so on. Similar to available synthetic methods of COFs, the preparation of iCOFs mainly is divided as direct synthesis and post-modification strategies. Some iCOFs were applied in solid-phase extraction field (cartridge solid-phase extraction, dispersive solid-phase extraction, and magnetic solid-phase extraction) and displayed excellent extraction performance. In this paper, their preparation methods and detailed applications for solid-phase extraction are reviewed, and the extraction mechanism including electrostatic, π-stacking, hydrogen-bonding, hydrophobic interactions, etc. for various analytes is also discussed. Through designable ionic monomers or facile post-modification ways, task-specific iCOFs can be developed for sample preparation and other fields. As one type of popular materials, the challenges and development trends of iCOFs are also presented.