Morphology-Dependent Structural Evolution of Co3O4 from Co-ZIFs during Thermal Decomposition

Abstract

The thermal decomposition of zeolitic imidazolate frameworks (ZIFs) into metal oxides is a promising route for creating nanostructured materials, yet a systematic understanding of the structural evolution mechanism remains limited. This study investigates the synergistic effects of precursor morphology and calcination temperature on the formation of Co3O4 from cobalt-based ZIFs (Co-ZIFs). Co-ZIF precursors with distinct three-dimensional (3D) polyhedral and two-dimensional (2D) sheet-like morphologies were synthesized by modulating solvent systems and reactant concentrations. Their transformation into Co3O4 via calcination in air was systematically studied using SEM, XRD, TGA-DSC, and Raman spectroscopy. The results reveal that the precursor morphology dictates the thermal decomposition pathway: 3D polyhedral evolve into hollow structures via the Kirkendall effect, while 2D sheets exhibit excellent morphological inheritance, forming hierarchical assemblies. Critically, the calcination temperature regulates the content and role of residual carbon species, which initially constrain the lattice at lower temperatures and subsequently drive crystalline refinement upon their removal at higher temperatures. This work elucidates the cooperative mechanism between morphological templating and thermal dynamics, providing fundamental insights for the rational design of MOF-derived functional oxides.