Dual-Mechanism Insights into the Peroxidase-like Activity of Co<sub>3</sub>O<sub>4</sub> Nanoparticles: Nonradical and Superoxide Radical Catalysis
Shufeng Liang, Yun Zhao, Yunhui Zhang, Xing Zhao, Miaomiao Li, Yunpeng Wang, Hui Han, Yanling Yu, Yan Dai, Yujing Guo
Abstract
Although the Co 3 O 4 nanozyme has been reported to exhibit peroxidase (POD) mimicking activity, its explicit catalytic mechanism remains indefinable. This study systematically investigates the POD-like catalytic mechanism of Co 3 O 4 nanoparticles (NPs) through integrated experimental and theoretical approaches. The results reveal that their catalytic activity originates from dual synergistic pathways: the nonradical and the radical pathways. In the nonradical pathways, Co 3 O 4 NPs mediate electron transfer from the substrate (e.g., 3,3′,5,5′-tetramethylbenzidine, TMB) to H 2 O 2 through the Co(III)/Co(II) redox couple, as its redox potential lies between that of TMB and H 2 O 2 . During the radical pathways, electron paramagnetic resonance (EPR) and fluorescent or UV–vis probe experiments demonstrate that H 2 O 2 preferentially decomposes into superoxide radicals (O 2 •- ) over hydroxyl radicals ( • OH). Furthermore, density functional theory calculations reveal that H 2 O 2 exhibits a relatively lower activation barrier (0.78 eV) to generate O 2 •- on the Co 3 O 4 (110) facet, compared to the higher barrier (1.72 eV) for • OH formation. Additionally, the distinct degradation behaviors of organic dyes provide further validation of the proposed mechanism. This research will encourage further exploration into the catalytic mechanisms of nanozymes, thereby facilitating their rational design and application.