Comparative non-isothermal kinetic and thermodynamic analysis of Fe3O4 and CoFe2O4 spinel ferrite nanoparticles by multi-heating-rate thermogravimetry

Spinel ferrites continue to attract significant interest owing to their composition dependent multifunctionality and tunable physicochemical properties at the nanoscale. Although the synthesis and structural characterization of Fe3O4 and CoFe2O4 nanoparticles have been reported previously, systematic comparative investigations of their non-isothermal thermal kinetics and thermodynamic behaviour remain limited. Comprehensive thermogravimetric and differential thermal analyses (TG-DTA) performed at heating rates of 10–25 K min−1 revealed a two distinct mass-loss stages associated primarily with the removal of surface-associated species at lower temperatures and thermally induced structural relaxation together with residual mass-loss processes at higher temperatures. The non-isothermal kinetic parameters were evaluated using the model-free Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) isoconversional methods. The calculated activation energies ranged from 138–275 kJ mol−1 for Fe3O4 and 57–196 kJ mol−1 for CoFe2O4, demonstrating the superior thermal stability of Fe3O4. Thermodynamic analysis provided positive activation enthalpy (ΔH*) and Gibbs free energy (ΔG*) values together with negative activation entropy (ΔS*) values, indicating the formation of a more ordered activated complex and that the thermal mass-loss processes require continuous energy input. The comparative kinetic and thermodynamic analyses demonstrate that cation composition significantly influences the thermal stability of spinel ferrite nanoparticles and provide valuable information for understanding their thermal behaviour and optimizing their utilization in high-temperature magnetic, catalytic, and energy-related applications.