Core–Shell Heterostructured Composite Architected from a Multilanthanide-Included Phospho(III)tungstate and MIL-(53)Fe as a Nanozyme for Catalytic Oxidation of 3,3′,5,5′-Tetramethylbenzidine

The development of novel multicomponent nanozymes with high catalytic efficiency and selectivity continues to be a focal point in contemporary research. In this work, a multilanthanide-containing phospho(III)tungstate [H₂N(CH₃)₂]₈Na₁₂H₁₆[La₄(H₂O)₁₅W₈(tart)₃(H₂tart)O₂₀]₂[H₂P₂W₁₄O₅₂]₄·52H₂O (1, H₄tart = tartaric acid) was synthesized. Its polyoxoanion consists of two identical tartrate-stabilized tetra-La³⁺-substituted {La₄(H₂O)₁₅W₈(tart)₃(H₂tart)O₂₀} units bridged by four multivacant Dawson-like [H₂P₂W₁₄O₅₂]¹²⁻ fragments. Subsequently, 1 was subjected to ultrasonic treatment to form a nanofilm, which was then used as a guest material to coat MIL-(53)Fe (MILFe), preparing a series of core-shell heterostructured MILFe@1 composites. These MILFe@1 composites facilitate multielectron transfer and function as highly active nanozymes, significantly enhancing the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Under optimized conditions, the MILFe@1-2 (1: MILFe = 1:2) composite demonstrates robust catalytic performance over a broad TMB concentration range without the need for H₂O₂. This work highlights the potential of integrating lanthanide-containing polyoxometalates with metal-organic frameworks to construct core-shell heterostructured nanozymes with enhanced catalytic efficiency. Concurrently, the polyoxometalate shell enables rapid electron transfer kinetics, which is crucial for enhancing the overall catalytic performance of the system.