Figure 2 a Low and b high-magnification SEM images of ZnCo2O4; c SEM images of Ag3PO4; d SEM images of ZnCo2O4/Ag3PO4;e TEM image of ZnCo2O4/Ag3PO4;f HRTEM image of ZnCo2O4/Ag3PO4and g SAED pattern of ZnCo2O4/Ag3PO4.
Fig. 2a shows the spherical ZnCo2O4successfully synthesized by the microwave-assisted method with a diameter range of 3–8 μm. Fig. 2b shows the structure of a single ZnCo2O4 microsphere, which can be seen from the figure as a stack of nanosheets. Fig. 2c shows Ag3PO4 crystals with a regular hexahedral structure and a particle size range of 0.4–1 μm. Fig. 2d is an SEM image of the composite ZnCo2O4/Ag3PO4. It can be seen from the figure that the particle size range of ZnCo2O4/Ag3PO4is also 0.4–1 μm, which is caused by the recrystallization of ZnCo2O4 and deposition on Ag3PO4 during the synthesis process. To further observe the morphology of ZnCo2O4/Ag3PO4, Fig. 2e shows the TEM image of ZnCo2O4/Ag3PO4, from which it can be seen that the recrystallized ZnCo2O4 is attached to the Ag3PO4 crystal surface. Fig. 2f shows the HRTEM image of ZnCo2O4/Ag3PO4, which further verifies that the recrystallized ZnCo2O4 is successfully attached to the Ag3PO4 crystal surface, and the lattice spacing d is 0.244 and 0.269 nm for ZnCo2O4 and Ag3PO4, corresponding to the (220) and (210) crystal planes of ZnCo2O4 and Ag3PO4, respectively. Fig. 2g shows the SAED plot of ZnCo2O4/Ag3PO4, in which the bright diffraction rings of ZnCo2O4/Ag3PO4can be seen, indicating that it is polycrystalline. In addition, the lattice distances of 0.244 nm and 0.269 nm for the two crystal planes can be clearly seen in Fig. 2g, which is in agreement with the results of HRTEM plots. In summary, it can be clearly seen that the composite catalyst ZnCo2O4/Ag3PO4is formed by loading the recrystallized ZnCo2O4 onto the Ag3PO4 crystal surface.