Two-step synthesis of agglomeration-free peroxidase-like Co3O4nanoparticles–carbon nitride nanotube hybrids enabling a high redox activity

Abstract

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.