Implications on Structural, Morphological, and Optical Properties and Photocatalytic Degradation Behavior of Zinc Oxide Nanoparticles: Effect of Calcination Temperature

ZnO nanoparticles synthesized via co-precipitation were calcinated at different temperatures (300 °C, 500 °C, and 700 °C) followed by their structural, morphological, photocatalytic, and optical properties, and characterized by using X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), UV-visible and Fourier-transform infrared (FTIR) spectroscopy. The XRD spectra of ZnO nanoparticles indicated a shift of the characteristic XRD peak towards lower angles from 31.62° to 31.83°, 34.24° to 34.49°, and 36.11° to 36.37°, respectively, with calcination. The crystalline size of the calcinated ZnO nanoparticles increased from 33.5 to 45.5 nm and from 30.2 to 37.8 nm, calculated by Rietveld refinement and Scherrer’s method. The UV-visible spectrum showed absorption bands at 468 nm and 671 nm, respectively. A Tauc plot has been drawn from the absorption spectra from UV data, and the range of the optical energy bandgap of the calcinated samples lay between 3.67 ± 0.07 and 3.35 ± 0.02 eV. SEM and EDX confirmed the presence of Zn and O in the ZnO nanoparticles. The intensity of the absorption decreased steadily with increasing UV irradiation time for each annealed sample. The reduction in photocatalytic activity of the calcined Zinc oxide (ZnO) samples can be linked to the simultaneous decrease in both oxygen vacancies and surface-bound oxygen species.