In this research, Zn-Co3O4 solid solution (ZCH) nanoparticles have been synthesized by hydrothermal method calcined at the different temperature (300, 400, 500 °C). Cobalt nitrate hexahydrate (Co(NO3)2.6H2O) and Zinc nitrate hexahydrate (Zn(NO₃)₂.6H₂O) have been used as sources of Co3O4 and Zn cation. X-ray diffraction (XRD), UV-Vis spectrophotometer, BET analysis, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) have been used to investigate the structural, optical, surface area, photocatalytic and morphological properties of nanoparticles. The results showed that the calcination temperature has a significant effect on the microstructure, optical and photocatalytic activity of the samples. The crystallite size of ZCH nanoparticles is about 8, 11 and 14 nm respectively at the calcination temperature of 300, 400 and 500 °C. The calcined solid solution sample at 400 °C (ZCH-400) has shown higher photocatalytic degradation under visible light irradiation than the other two temperatures. The percentage of degradation of methylene blue in the presence of this sample was about 13.83% in 1 hr. Increasing the calcination temperature from 300 to 500 °C has led to a decrease in the band gap from 1.48 to 1.38 eV for ZCH samples.
