Deciphering the effect of calcination temperature on crystallinity, morphology, oxygen vacancy and photocatalytic activity of bi-phasic ZnO/ ZnCo2O4 heterostructured nanomaterials

This study investigates the synthesis of cobalt incorporated zinc oxide (ZnO) metal oxide via co-precipitation followed by calcination at varying temperatures ranging from 300 degrees C to 700 degrees C. X-ray diffraction analysis revealed the presence of two crystallite phases, hexagonal ZnO and wurtzite ZnCo2O4, at temperatures between 500 degrees C and 700 degrees C, while only the ZnO phase was observed below 500 degrees C with ZnCo2O4 remaining amorphous. Morphological evolution revealed the gradual development of a rod-shaped morphology for ZnO phase, reaching peak stability at 500 degrees C, beyond which the structural rupture occurred. The impact of temperature on oxygen vacancy, surface area, optical band gap energy, and recombination of charge carriers was investigated. Photocatalytic activity against MO dye demonstrated an increase with calcination temperature up to 500 degrees C, attributed to improved crystallinity. Notably, the sample annealed at 500 degrees C exhibited the highest photocatalytic activity due to its highly ordered crystallinity, bi-phase composition, and appropriate band gap. However, further increase in calcination temperature led to a rapid decrease in photocatalytic activity due to morphological destruction and loss of crystallinity. These findings highlight the importance of optimizing calcination temperature to tailor the crystallinity, morphology, and photocatalytic activity of mixed metal oxides, offering insights for controlled material synthesis with desired properties.