Superior performance of 3 D Co-Ni bimetallic oxides for catalytic degradation of organic dye: Investigation on the effect of catalyst morphology and catalytic mechanism

• Four NiCo2O4 with diverse morphologies were prepared and used in MICD process.
• Morphology-dependent catalytic activity of NiCo2O4 for dye was discovered.
• Hierarchical structure and high MW utilization facilitated activity of NiCo2O4-S.
• A band-gap model was proposed to accurately predict types of active species in MICD.
• A possible catalytic mechanism of 3D NiCo2O4-S was revealed in detail.

An application of novel magnetic separable NiCo2O4 in microwave-induced catalytic degradation (MICD) of organic dye was found, and the structures of NiCo2O4 significantly affect its catalytic activity. Diverse NiCo2O4 structures, including NiCo2O4 nanoplates (NiCo2O4-P), NiCo2O4 nanorods (NiCo2O4-R), NiCo2O4 nanoparticles (NiCo2O4-N) and three-dimensional (3D) hierarchical dandelion-like NiCo2O4 spheres (3D NiCo2O4-S), have been successfully synthesized. Among them, 3D NiCo2O4-S displayed superior catalytic activity for congo red (CR) under microwave (MW) irradiation. Enhanced catalytic activity of 3D NiCo2O4-S can be attributed to the higher MW energy harvesting capacity resulted from multiple absorption of MW and relatively high specific surface area. Various scavengers, the band structure, as well as Mott–Schottky analysis, were utilized to identify the roles of active species. A possible catalytic mechanism was proposed. The 3D NiCo2O4-S is expected to have potential applications in pollutants degradation because of its efficient catalysis, easy separation and good reusability.

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