Hydrogen-Bond-Assisted Secondary Amine-Phosphonate Tandem Sites on Mesoporous Nano-Silica for Uranyl Carbonate...

The selective capture of uranium from alkaline radioactive wastewater remains highly challenging because uranyl carbonate complexes, particularly [UO₂(CO₃)₃]^4-, possess remarkable thermodynamic stability and electrostatic repulsion from negatively charged adsorbent surfaces. Herein, we report a secondary-sphere activation strategy by constructing secondary amine-phosphonate tandem sites within mesoporous nano-silica channels (GP@SiO₂-APTES) for efficient uranyl carbonate capture. The rationally integrated secondary amine groups and phosphonate moieties establish a cooperative binding microenvironment, in which hydrogen-bond-donating secondary amine sites facilitate carbonate activation while adjacent phosphonate groups provide strong uranium coordination. As a result, GP@SiO₂-APTES achieves a remarkable adsorption capacity of 348.8 mg g^{- 1} toward [UO₂(CO₃)₃]^4- under alkaline conditions (pH 8-10), significantly outperforming monofunctional control materials. Combined spectroscopic analyses and density functional theory calculations reveal that the secondary amine-assisted secondary coordination environment weakens uranyl-carbonate interactions and promotes phosphonate-mediated uranium binding. Moreover, the hybrid silica framework exhibits excellent operational durability, retaining over 99% uranium removal efficiency after 250 kGy γ-irradiation and five adsorption-desorption cycles. This work demonstrates a molecular design strategy that employs hydrogen-bond-assisted secondary coordination to facilitate the capture of stable metal complexes, providing new opportunities for advanced actinide separation materials.