Figure 2. XRD patterns of Co-P (a); Cu-P (b); Cu-Co-xP-2(x= 1, 2, 3, 4. ) (c); Cu-Co-2P-x(x= 1, 2, 3, 4. ) (d).
The SEM images are shown in Figure 3, displaying the morphology characteristics of Cu-MOFs, ZIF-9(Co) and Cu-MOFs@ZIF-9(Cu-Co-2) as well as the samples after phosphating. In Figure 3(a), the sample of Cu-MOFs exists as a regular octahedron, and the surface is relatively flat. ZIF-9(Co) displays the morphology of the 2D nanosheet which is well-shaped and has averaged size (Figure 3(b)). When ZIF-9(Co) grows on the surface of Cu-MOFs, the growth of 2D nanosheets is suppressed to a certain degree. Therefore, ZIF-9(Co) on the surface of Cu-MOFs in the Cu-Co-2 composite sample shown in Figure 3(c) exists in the form of fibrous rods or small pieces. Cu-P, Co-P and Cu-Co-2P-2 composite samples were obtained by phosphating Cu-MOFs, ZIF-9(Co) and Cu-Co-2 samples, as shown in Figure 3(d-f). Cu-P samples almost do not have regular geometric shapes, showing larger particles and more denser. The SEM image of Co-P obtained from the phosphorization of Co-MOFs of 2D nanosheets is shown in Figure 3(e). In Figure 3(e), Co-P shows a very uniform and fine flaky structure. The SEM image of Cu-Co-2P-2 sample obtained by phosphating the Cu-MOFs@ZIF-9(Cu-Co-2) sample is shown in Figure 3(f). In the composite sample, the surface of Co-MOFs is almost completely phosphatized, showing a small plate shape, and Cu-MOFs inside still have a small number of regular three-dimensional structures. Combined with XRD analysis, it can be seen that the phosphorization of Cu-MOFs is not complete, so there will be a small number of regular octahedral structures in Figure 3(f).