Sulfone Molecular Switch Enables Direct Two-Electron Uranium Photoreduction in Programmed Covalent Organic Frameworks.

Abstract

Photocatalytic uranium extraction from seawater is indispensable for sustainable nuclear energy, yet its efficiency is fundamentally limited by the prevailing indirect superoxide-mediated reduction pathway, which suffers from sluggish kinetics, oxygen dependency, and poor selectivity. Herein, it is demonstrated that a molecular-level "sulfone switch", integrated into a covalent organic framework via edge-hanging engineering, orchestrates a decisive shift from the indirect to a direct two-electron transfer pathway for uranium photoreduction. The optimized Py-DaSO-COF achieves a remarkable uranium extraction capacity of 21.25 mg g^-1 in natural seawater, which is coupled with rapid kinetics and high selectivity against vanadium ions, surpassing most reported photocatalytic systems. Notably, combined experimental and theoretical studies reveal that the electron-deficient thiophene sulfone group promotes exciton dissociation, stabilizes key *UO₂ intermediates, and suppresses •O₂ ^- generation by diverting electrons directly to adsorbed uranium species. This work establishes a versatile molecular engineering strategy for controlling photocatalytic pathways, highlighting its universal significance for solar-driven resource recovery and beyond.