3.1.2 Morphology of the CMNR

The morphologies of Ti membrane substrate, ZIF-8/Ti membrane and Cu/ZnO/Ti CMNR could be observed through Figure 6. The porous structure and smooth surface could be clearly observed for the Ti membrane substrate from Figure 6(A1, A2). The pores can be still observed after ZIF-8 and Cu/ZnO has been immobilized in membrane pores (Figure 6(B1, C1)). This phenomenon implied that the pores of the Ti membrane substrate cannot be blocked by the immobilization nanoparticles. And numerous nanoparticles could be observed in membrane pores (Figure 6(B1, B2)). Besides, the Ti membrane substrate, ZIF-8/Ti membrane and Cu/ZnO/Ti CMNR were cut off and the cross-sectional morphology characteristics were observed. It could be observed that there was no nanoparticle distributed in the pores of Ti membrane substrate and the sintered bulk metal piled up to form an open pore structure, as shown in Figure 6(A3). After the Zn²⁺ solution and 2-mIm solution were permeated through the Ti membrane substrate in turn, the coordination reaction between Zn²⁺ and 2-mIm resulted in the formation of a large amount of 2D flake-shaped ZIF-8³³ in the pores of Ti membrane substrate with the average particle size of ZIF-8 being 208 nm, as shown in Figure 6(B3) and Figure S7(A). The Cu²⁺ solution was permeated through the ZIF-8/Ti membrane and then calcined at 360 ℃ under H₂/N₂ environment and spherical Cu/ZnO nanoparticles were successfully immobilized in membrane pores with an average particle size of 82 nm, as shown in Figure 6(C3) and Figure S7(B). The TEM image of ZIF-8 nanoparticles in ZIF-8/Ti membrane was shown as Figure 6D, and the regular dodecahedron crystal of ZIF-8 can be clearly observed. The TEM and HRTEM images of Cu/ZnO nanoparticles in Cu/ZnO/Ti CMNR were shown as Figure 6E and Figure 6F, respectively. The distance of 0.260 nm and 0.181 nm belong to ZnO (002) crystal plane and Cu (200) crystal plane, which proved the Cu⁰ and ZnO were immobilized in the membrane pores successfully by calcination and reduction.