Tuning crystallinity and electronic structure of Co3O4 nanoparticles via hydrothermal time for improved photocatalytic dye degradation and statistical kinetic evaluation.

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.