Distinctive Two-Step Intercalation of Sr2+ into a Coordination Polymer with Record High 90Sr Uptake Capabilities

⁹⁰Sr²⁺remediationfrom acidic nuclear waste solution and contaminatedseawaterattracts great public attention but is very challenging because the removal performance toward soft Sr²⁺by traditional oxidic ion-exchange materials are greatly affected by hardcationsincluding H⁺, Na⁺, and Ca²⁺. We report a layered oxidiccoordination polymer[(CH₃)₂NH₂][ZrCH₂(PO₃)₂F] (SZ-4) showing a notable advance over existing ion-exchange materials in⁹⁰Sr removal efficiencies with elevated distribution coefficients and record-high uptake capacities underacidic conditions. Moreover, the removal of Sr²⁺is not significantly affected by the presence of a large excess of hard cations, leading to the successful cleanup of⁹⁰Sr-contaminated seawater samples. Such superior capabilities are directly visualized by well-refinedsingle-crystalstructures duringin situSr²⁺sorptionprocess, revealing a distinctive two-step intercalation mechani** and a unique soft cation uptake selectivity achieved through collaborative coordination by the host layer and the interlayerdimethylamine(DMA) as a softN-donor ligand.