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.