Complex Three-Dimensional Co₃O₄ Nano-Raspberry: Highly Stable and Active Low-temperature CO Oxidation Catalyst

Highly stable and active low-temperature CO oxidation catalysts without noble metals are desirable to achieve a sustainable society. While zero-dimensional to three-dimensional Co₃O₄ nanoparticles show high catalytic activity, simple-structured nanocrystals easily self-aggregate and become sintered during catalytic reaction. Thus, complex three-dimensional nanostructures with high stability are of considerable interest. However, the controlled synthesis of complex nanoscale shapes remains a great challenge as no synthesis theory has been established. In this study, 100 nm raspberry-shaped nanoparticles composed of 7⁻8 nm Co₃O₄ nanoparticles were synthesized by hydrothermally treating cobalt glycolate solution with sodium sulfate. Surface single nanometer-scale structures with large surface areas of 89 m²·g^-1 and abundant oxygen vacancies were produced. The sulfate ions functioned as bridging ligands to promote self-assembly and suppress particle growth. The Co₃O₄ nano-raspberry was highly stable under catalytic tests at 350 °C and achieved nearly 100% CO conversion at room temperature. The addition of bridging ligands is an effective method to control the formation of complex but ordered three-dimensional nanostructures that possessed extreme thermal and chemical stability and exhibited high performance.