Heterogeneous Nanostructure Design Based on the Epitaxial Growth of Spongy MoS_<i>x</i> on 2D Co(OH)₂ Nanoflakes for Triple-Enzyme Mimetic Activity: Experimental and Density Functional Theory Studies on the Dramatic Activation Mechanism

Abstract

In this study, we present a three-in-one catalytic platform for intrinsic oxidase-, peroxidase-, and catalase-like activity, which is enabled by epitaxial growth of the MoS _x nanosponge on 2D Co(OH)₂ nanoflakes [2D Co(OH)₂ NFs] (CoMo hybrids). First, the 2D Co(OH)₂ NFs are stripped from hierarchical three-dimensional Co(OH)₂ nanoflowers which are synthesized in an eco-friendly way via one-step surfactant-free chemical route. Next, the porous MoS _x nanosponge is decorated on the 2D Co(OH)₂ NFs' surface using a solvothermal process forming heterogeneous nanostructured CoMo hybrids. Finally, because of the host-guest interaction, that is, after the epitaxial growth of spongy MoS _x on 2D Co(OH)₂ NFs, the heterogeneous nanostructure of CoMo hybrids exhibits unpredictable triple-enzyme mimetic activity simultaneously. The mechanisms of the oxidase-like properties are investigated by density functional theory (DFT) calculations, and it is discovered that a simple reaction/dissociation of O₂ absorbed on Co-Mo thin films can explain the enhanced oxidase-like activity of the CoMo hybrids. In addition, the CoMo hybrids are also reproducible, stable, and reusable, that is, after 10 cycle uses, >90% mimic enzyme activity of the CoMo hybrids is still maintained. The oxidase-like activity of the CoMo hybrids enables it to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) producing the blue oxTMB, which can selectively oxidize ascorbic acid (AA) and pave a new avenue for colorimetric sensing of AA. The proposed colorimetric strategy has been successfully utilized to measure AA in rat brain during the cerebral calm/ischemia process. Our findings provide in-depth insight into the future research of enzyme-like activities and might help to elucidate the mechanism and understand the role of epitaxial growth on the properties and application of hybrid nanostructures.