Yanhui Feng, Linghong Han, An Xu, Xueying Liang, Xiumei Lin, Hongxu Guo
The catalytic efficiency of nanozymes is governed by their surface electronic structure and defect chemistry, yet the synergistic regulation of oxygen vacancies (OVs) and mixed-valence states remains challenging. Herein, we report a ternary core-shell heterostructure, Cu/Cu2O/CuVO3@MOF(Cu-His-BDC)(CCVO@@MOF(Cu-His-BDC)), constructed via an in situ dual-ligand coordination strategy using histidine and terephthalic acid. This dual-ligand architecture enriches surface oxygen vacancies (33.86% → 59.87%) and reshuffles valence equilibria (V4+: 10.75% → 29.21%; Cu+: +10.21%), while creating a hierarchical porous network. Spectroscopic and electrochemical characterizations reveal that the enhanced oxidase-like activity stems from coupled ROS generation and interfacial electron transfer. Interestingly, Cr(VI) acts as a bifunctional regulator, triggering metal valence cycling (Cu+/V4+ ⇌ Cu2+/V5+) to amplify colorimetric signals while suppressing electrochemical responses. Leveraging this orthogonal promotion-inhibition effect, a dual-mode platform covering pM to μM ranges is established with recoveries of 94-107% in complex matrices. Combined with EDTA masking and alkaline persulfate oxidation, the platform enables reliable Cr(VI)/Cr(III) speciation, validated by ICP-MS, while smartphone-based RGB readout offers field-deployable capability. This work establishes a design paradigm for intelligent nanozymes through synergistic ligand and defect modulation.