Mechanistic elucidation of dye degradation over light-activated Co-MOF-derived Co₃O₄ nanoparticles via experimental...

This study describes cobalt oxide nanoparticles (Co₃O₄ NPs) produced by calcining a hydrothermally prepared metal-organic framework (Co-MOF) precursor. They were then thoroughly characterized to interpret their photocatalytic properties by a detailed analytical investigation of the experimental data. Phase-pure cubic spinel Co₃O₄ NPs were confirmed by X-ray diffraction with an average crystallite size of ∼22 nm. FT-IR was performed to investigate the phase obtained through Co-O bonding. Electron microscopy revealed a porous, flower-like structure, while elemental analysis (EDAX) confirmed the presence of cobalt and oxygen as the primary constituents. UV-vis spectroscopy analysis was performed to determine the optical properties, and photoluminescence measurements revealed clear defect-related emissions, indicating the presence of intrinsic defect states. The improvement in photocatalytic activity was explained by extensive theoretical calculations from characterization techniques such as crystallographic parameters, lattice strain, dislocation density, optical band gap, absorption behavior, and defect-related electronic features. All these factors influence the efficiency of light harvesting, the generation of charge carriers, transport, and recombination dynamics. Based on a range of structural, optical, and defect-related features, this work shows how their combined effect results in a substantial improvement in photocatalytic activity. A review of the literature has enabled the establishment of a comprehensive structure-property activity relationship entirely grounded on experimentally derived analytical insights, leading to a rational framework for the design of advanced MOF-derived photocatalysts. Co₃O₄ NPs showed excellent photocatalytic performance, degrading nearly 99.47% of Rhodamine B (Rh B) within 280 minutes and 99% of Thymol Blue (TB) within 140 minutes, while displaying faster degradation rates for TB, and they both exhibited pseudo-first-order kinetics as evidenced by their good linearities with R² values of 0.91 and 0.93, respectively.