We report a two-step synthesis method to fabricate peroxidase-like Co3O4 nanoparticles–carbon nitride nanotube (Co3O4 NPs–CNNT) hybrid catalysts enabling a high redox activity. At first, the energy-dispersive spectrometer mapping shows that the CNNT surface is wrapped by the Co(OH)2 after the first solvothermal step using cobalt acetylacetonate of Co(acac)3 precursor and triethylene glycol solvent. Also, the X-ray diffraction and photoelectron spectroscopy measurements support that the subsequent heat treatment transforms the Co(OH)2 into the crystalline Co3O4 NPs on the CNNT. Also, the near-edge X-ray absorption fine structure analysis and density functional theory calculations provide a clue regarding the role of pyridine- and graphite-like N atoms of the CNNT to anchor agglomeration-free Co3O4 NPs on its surface. Indeed, the Co3O4 NPs–CNNT hybrid shows high peroxidase-like redox activity for 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2. Furthermore, the electron spinning resonance analysis elucidates the mechanism for the high peroxidase-like redox activity, where the electrons of Co3O4 NPs and a CNNT first move to H2O2 and then H2O2 form one OH radicals and one OH ion. Next, TMB is oxidized by a Co3O4 NPs–CNNT hybrid and generates electrons. Then, the generated electrons offset to maintain the neutral state of a Co3O4 NPs–CNNT hybrid. The XRD data of a Co3O4 NPs–CNNT hybrid after the peroxidase reaction further supports our proposed model.
