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

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 MoSx 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 MoSx 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 MoSx 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.