The effect of temperature (from 300 to 600°C) of decomposition of the metal-organic framework ZIF-67 deposited on a glass FTO substrate coated with TiO2 nanotubes on the formation of the Co3O4 catalyst was studied. Using a set of physicochemical methods, such as powder X-ray diffraction, X-ray fluorescence analysis, and IR and UV-visible spectroscopy, various stages of the transformation of ZIF-67 into Co3O4 were revealed. The complete thermal destruction of ZIF-67 occurs at a temperature of 460°C, and the spinel phase is formed at 540°C. The elemental composition of the samples, obtained by X-ray fluorescence analysis, made it possible to identify three different regions of change in the Si/Sn/Ti/Co ratio depending on the calcination temperature. Before 380 and after 520°C, the composition of the samples changed relatively monotonously, while in the intermediate temperature range, a nonlinear change was detected. Based on the data obtained, two samples (Co3O4-440 and Co3O4-540) were selected and calcined at 440 and 540°C, respectively, after which their photoelectrochemical activity was estimated. Linear voltammograms showed higher photocurrent values for the Co3O4-440 sample with a smaller active surface area, calculated from the linear dependence of the current density difference on the scanning speed.
Polyakov et al. (Mon,) studied this question.