Dual-Functional Eu^2+/3+-Complex@ZIF-67 Nanocatalyst Derived from a Green Reduction of Eu³⁺ Compound

The Eu^2+/3+ mixed-valent complexes have aroused attention because of their potential application in the catalytic field endowed by the variable valence. Herein, we develop an ingenious green strategy to achieve the partial reduction of Eu³⁺ to Eu²⁺ ions in the complex of pyrenol-containing cyclen (H₄(Pyr)₄cyclen, H₄[PC]) via a ligand-to-metal charge transfer (LMCT) effect in air at room temperature. To reveal the inherent regulated capacity of the Eu^2+/3+ complex in catalysis, we prepared the nanocomposites assembled by the lanthanide complexes encapsulated into ZIF-67 to successively realize the decomposition of H₂O₂, including europium, gadolinium, and terbium complexes. Among the nanocomposites, Eu^2+/3+[PC]H@ZIF-67 exhibits the best catalytic performance due to the achievement of dual regulation of Co³⁺/Co²⁺ ratio by the mixed-valent complex. Because of extremely abundant Co²⁺ active sites, the Eu^2+/3+[PC]H@ZIF-67 after catalyzing H₂O₂ sample was further utilized to degrade organic dye rhodamine B (RhB). The rather outstanding catalytic degradation efficiency was still present in Eu^2+/3+[PC]H@ZIF-67. This research presents a facile strategy of Eu³⁺ reduction based on the ligand design and a new direction for the future development of the composite catalytic materials with mixed-valent complexes.