How Central Metal Ions in MOF Affect the Uranyl Elimination Performance: Insights from Experimental and Theoretical...

Conventional strategies for enhancing the performance of metal-organic framework (MOF) adsorbents primarily focus on modifying functional groups, while the critical role of central metal ions remains underexplored. Herein, a definitive structure-activity relationship governing uranyl (U(VI)) elimination by engineering isomorphic HHTP MOFs (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with Zn²⁺, Ni²⁺, and Cu²⁺ centers is revealed. Advanced characterization confirms that the identity of the metal dictates electronic configurations and binding thermodynamics without altering crystallographic topology. Remarkably, Zn-HHTP achieves a record U(VI) uptake capacity of 458.73 mg·g^-1, surpassing Ni-HHTP (441.27 mg·g^-1) and Cu-HHTP (317.24 mg·g^-1), coupled with ultrafast kinetics (80 min) and exceptional selectivity. Mechanistic studies reveal that the optimal electronegativity (χ = 1.65) of Zn²⁺ endows it with superior Lewis acidity, facilitating enhanced charge transfer (Δq = 0.065 e^-) via Zn─O─U coordination, as demonstrated by combined XPS analysis and DFT calculations. This lower electronegativity of Zn²⁺ promotes greater electron acceptance from U-O, yielding a robust binding energy (E_ads = -35.16 kcal·mol^-1). This work establishes the modulation of central metal ions as a critical design paradigm for next-generation MOF adsorbents, positioning Zn-HHTP as a transformative material for high-efficiency radioactive wastewater remediation.