Method-dependent structural evolution of Co3O4 nanoparticles synthesized via sonochemical, chemical precipitation, and hydrothermal routes.

The precise control of microstructural properties in Co3O4 nanoparticles is crucial for performance, however, the relationship between synthesis method, crystallite size, and lattice strain remains unclear. In this study, Co3O4 nanoparticles were systematically synthesized using three distinct methods: sonochemical, chemical precipitation, and hydrothermal, to evaluate the method-dependent evolution of their structural characteristics. Phase purity and crystalline structure were rigorously analyzed using X-ray diffraction (XRD), while the Debye-Scherrer equation and the Williamson-Hall method were employed to quantitatively decouple the effects of finite crystallite size and internal microstrain on peak broadening. Key results demonstrate that the synthesis route is a decisive factor in structural tailoring: chemical precipitation yielded the smallest crystallite size (12.1 nm) with the highest dislocation density (6.83 × 10-3 nm-2), suggesting a defect-rich surface that may enhance catalytic activity. Conversely, the hydrothermal method produced a higher degree of crystallinity with low dislocation density (0.88 × 10-3 nm-2), but introduced higher residual microstrain (2.49 × 10-3) due to rapid growth dynamics. TEM characterization results confirmed the formation of irregular and quasi-spherical morphologies, along with size distribution analysis. UV-Vis spectroscopy revealed two distinct absorption bands corresponding to ligand-to-metal charge transfer (LMCT). A noticeable reduction in the optical band gap was observed for the Co3O4-CP sample. This shift is directly associated with increased lattice strain identified in structural analysis and quantum confinement effects. SEM and EDS results indicated that the synthesis method strongly affects the morphology of Co3O4, while confirming the homogeneous presence and distribution of cobalt and oxygen throughout the samples. These findings provide a strategic roadmap for selecting synthesis parameters to engineer Co3O4 nanostructures with specific defect densities and strain profiles for targeted industrial applications.