Tuning crystallinity and electronic structure of Co₃O₄ nanoparticles via hydrothermal time for improved...

This study explores photodegradation using needle-like Co₃O₄ NPs with time-dependent morphology, fabricated using a hydrothermal method with different hydrothermal reaction times (12 h, 24 h, 48 h, and 72 h), as a photocatalyst for organic dye degradation under simulated solar light irradiation. XRD, FTIR spectroscopy, SEM, EDX, diffuse reflectance spectroscopy (DRS), and BET analyses were used to characterize the prepared Co₃O₄ NPs. A notable temperature-dependent transition in crystallinity and phase composition, coupled with a notable reduction in lattice strain and refinement of the grain size at higher temperatures, was observed. The results demonstrated a decrease in band gap from 3.53 eV to 3.46 eV as the hydrothermal reaction time increased progressively, implying higher electronic structural ordering and improved light-harvesting capabilities. Selectivity studies on degrading the EY and BF dyes at 5 ppm showed distinct responses for catalysts with different Co₃O₄ preparation times. Co₃O₄ NPs synthesized over 48 h with 6.5 m² g^-1 loading exhibited high selectivity for EY and BF, with 71.2% and 76.9% degradation, respectively. Kinetics were analyzed using pseudo-first-order models and Minitab software to evaluate the experimental data and model the reaction behavior, with a statistically significant p-value of ∼0.000. Recyclability tests demonstrated that Co₃O₄ was highly stable under simulated solar light dye degradation conditions. The enhanced photocatalytic activity of Co₃O₄ NPs is likely due to the optimized hydrothermal reaction time that resulted in Co₃O₄ NP structures with reduced charge recombination and increased catalytic activity. The findings demonstrate the importance of hydrothermal reaction time for designing 48 h Co₃O₄ nanostructures with optimized structural features and better photocatalytic activity.