A Key to Crystallinity and Reusability of Covalent Organic Frameworks: Adsorption-Induced Deformation

The design and synthesis of covalent organic frameworks (COFs) with excellent reusability are promising ways to advance practical applications in many fields, including as absorbents for environmental remediation. However, a lack of guiding principles makes it challenging. Herein, two COFs (DhaTAT and DhaTAB) are prepared and demonstrated to work excellently for the adsorption and removal of the representative environmental pollutant phenanthrene (PHE) with the highest adsorption capacity and the fastest adsorption kinetics reported so far. Although having comparable PHE adsorption performances, DhaTAT displays much better reusability than DhaTAB. By deeply exploring the underlying mechanism, we reveal for the first time the adverse effects of adsorption-induced deformation phenomenon on the crystallinity, morphology, specific surface area, and thus reusability of COFs, and propose that introducing electron-withdrawing groups can alleviate this phenomenon and endow COF-based adsorbents with excellent reusability. Such a prediction is further confirmed by the recycling performances of two new COFs (DapTFB and DanTFB) that are designed under the guidance of theoretical calculations. This study provides valuable insights into the effects of adsorption-induced deformation on the practical application potential of COFs, which is crucial for the development of new materials with stable adsorption performance and good reusability.