Revealing Moderate Lewis Acidity of Cerium Enhancing Hydrolytic Activity of MOF-Based Nanozymes

The hydrolytic activity of nanozymes against organophosphorus nerve agents is related to the Lewis acidity (LA) of the metal sites, but no direct correlation has been identified. Understanding the influence mechanism of LA on activity is crucial for the rational design of nanozymes. Herein, M-NU-1200 is utilized with metal sites having different LA (M = Ce, Zr, and Hf) to evaluate, to the best of our knowledge, the impact of varying LA on the hydrolytic activities of nerve agent simulants. Solid precursors (Ce₆ clusters) are utilized to synthesize Ce-NU-1200 with a uniform cubic morphology, enabling direct comparison of the activities among M-NU-1200. Our study reveals that Ce-NU-1200 exhibits notably higher catalytic performance compared to its analogs and surpasses the most advanced materials reported so far (K_cat/K_m = 533 M^-1 min^-1). This high performance can be attributed to the moderate LA of Ce sites, which promotes the polarization of the phosphorus center, electron withdrawing and transfer at M₆O₈ sites, and imparts the neighboring M-OH with enhanced electronegativity for nucleophilic attack. It is illustrated that effective Lewis acidity (eLA), defined as the acidity of metal-ligand coordination, is the highest for Ce-NU-1200 and directly correlated with the hydrolytic activity of nanozymes.