Water-Cluster-Expanded Interpenetrated Covalent Organic Frameworks Create High-Affinity Coordination Microenvironments for Efficient Strontium Capture

The efficient capture of radioactive strontium (Sr2+) from nuclear-contaminated water is of critical importance for environmental safety and public health protection. Three-dimensional covalent organic frameworks (3D COFs) with multi-interpenetrated architectures offer the potential for multidentate synergistic coordination toward target Sr2+. However, the confined internal environment arising from uncontrolled multi-interpenetration often restricts coordination freedom, while the concomitant reduction in pore size and obstruction of transport channels impose significant kinetic limitations on the adsorption process. Herein, we report a water-cluster-induced framework swelling strategy implemented in our synthesized 3D TB-COF adsorbent. This approach simultaneously establishes a multisource coordination environment that enhances both Sr2+ affinity and selectivity, and expands the pore channels to eliminate transport barriers, reduce mass-transfer resistance, and improve active-site accessibility. The water-expanded TB-COF adsorbent achieves a record-high maximum adsorption amount (qmax = 346.2 mg g–1) and excellent selectivity in simulated nuclear wastewater, alongside outstanding radiation tolerance. Combined experimental and theoretical analyses reveal that the superior Sr2+ recognition originates from the water-cluster-modulated coordination space constructed by three adjacent networks. This work provides a general design strategy for developing advanced 3D interpenetrated COF adsorbents toward environmental remediation of nuclear contamination.