Unravelling the microscopic interactions underlying uranyl species adsorption by charged COFs: A molecular dynamics simulation study

•First proven spontaneous adsorption of three uranyl species onto charged COFs.•Capture real-time interactions of uranium adsorption in COFs using MD simulations.•Frist proposed a novel cation-mediated co-coordination adsorption mechanism.•Uranyl species adsorbed in COFs via hydrogen bonds or coordination interactions.•MD simulations helped to understand how uranium adsorbs in charged COFs. Covalent organic frameworks (COFs) are highly efficient materials for removing toxic and radioactive uranium contaminants from water, yet the molecular interactions governing uranium adsorption in COFs remain insufficiently understood. In this study, molecular dynamics (MD) simulations were employed to investigate the adsorption behaviors of three uranyl species —UO22+, UO2CO3, and UO2(CO3)34-—in COFs functionalized with charged sulfonic acid groups (-SO3-). Two distinct adsorption mechanisms for different uranyl species were identified: (i) an ion-exchange mechanism, where UO22+ replaces the counterions (which is Na⁺ in this work) originally adsorbed in COFs pores and forms hydrogen bonds with -SO3- or carbonyl groups through water molecules in its hydration shell; and (ii) a cation-mediated co-coordination mechanism, where UO2CO3, particularly UO2(CO3)34- coordinate with Na⁺ to form stable complexes, which are then adsorbed onto -SO3- through coordination interactions. These findings demonstrate the ability of charged COFs to adsorb various uranyl species, including like-charged ones. The simulations also reveal that hydrogen bonding and coordination interactions influence the tilt angle of uranyl ions during adsorption and their entry into COFs pores. These insights enhance our understanding of uranium adsorption in charged COFs and highlight their potential for broad-spectrum uranium removal. [Display omitted]