Polyimide Covalent–Organic Frameworks for Aqueous Actinide Sequestration: Combined Ab Initio and Molecular Dynamics Studies

The sustainable expansion of nuclear power hinges on the effective management of actinide-containing waste streams, particularly through the capture and recovery of plutonium and uranium. Selective sequestration of these actinides is crucial not only for environmental remediation but also for recycling these finite and nonrenewable resources in advanced nuclear fuel cycles. Covalent-organic frameworks (COFs) have emerged as next-generation sorbents, offering versatile structural designs, exceptional surface areas, and precisely tunable binding sites to enable highly selective sorption and efficient regeneration. In this in silico study, we evaluate a series of polyimide COFs (PI-COFs) for their ability to detect and capture radioactive actinides, UO₂²⁺ and Pu⁴⁺, from aqueous solutions. We employ a multiscale computational approach that combines ab initio density functional theory (DFT) calculations with molecular dynamics (MD) simulations to characterize the energetics and diffusion dynamics of adsorbates within adsorbent frameworks. Our results show that PI-COF-1 displays the strongest adsorption for UO₂²⁺, while PI-COF-3 exhibits the highest adsorption energy for Pu⁴⁺ and correspondingly strong selectivity. The combined adsorption and diffusion trends reveal how the stacking arrangement and nitrogen-rich functional groups strengthen host-guest interactions and modulate ion transport. These insights identify specific PI COF structural features that promote efficient actinide sequestration and provide guidance for targeted experimental validation and material optimization.