## 3 Results and Discussion  
### Morphology and Characterization of the CuBTC@PET Membranes  
#### 3.1.1 PET Electrospun Fiber Morphology Study  
The one-factor control microscopic morphology of PET fiber membrane prepared by electrostatic spinning is shown in Figure 2; the SEM images shown are all magnified 30,000 times. The spinning parameters of Figure 2A are as follows: TFA/DCM is 1:1; PET 12 wt%; 16 kV; 1 mL/h. The diameter distribution is more uniform, with an average diameter of 374.22 \(\pm\) 70.56 nm. The effect of the solvent system on the morphology of the fibers can be seen by observing Figure 2A-C. Researchers generally believe that TFA/DCM is a better solvent for PET electrostatic spinning [37,38]. TFA has a high dielectric constant and low surface tension (42.1 N/m and 13.63 dyn/cm), and as a good solvent for PET, it can be effective in stretching droplets to form a stable jet. DCM has a low dielectric constant and high surface tension (8.9 N/m and 28.12 dyn/cm), and as a co-solvent, it can be used as an auxiliary solvent to control the fiber size through the adjustment of the ratio. As shown in Figure 2B, the ratio of TFA/DCM is 1:2, and when the ratio of DCM is higher, the fibers cannot be completely stretched because the electric field force can not overcome the excessive surface tension of the solution, resulting in leading defects in the fibers and extremely non-uniform fiber distribution. When the ratio of solvent increases, as shown in Figure 2C, it leads to a decrease in the surface tension of the solution, and the phenomenon of Taylor cone instability and uneven fiber diameter distribution occurs during the spinning process. Figure 2D,E shows the micrographs under 10 wt% and 14 wt% PET. As shown in Figure 2D, a lower concentration resulted in the polymer droplets not being fully stretched in the needle, and the droplets dropped on the fiber membrane without being fully stretched by the electric field force to form leading defects. When the PET concentration was further increased, the solution surface tension was subsequently increased, leading to a decrease in the solution spinning and splitting ability, and the fiber diameter was subsequently increased, as shown in Figure 2E [39,40]. The control at different voltages is shown in Figure 2F.G. At 14 kV, due to the small electric field force, the speed of the spinning jet is insufficient, and the solvent evaporates slowly, resulting in the phenomenon of fiber adhesion and aggregation, which is mainly because the electric field force is insufficient to stretch the solution jet sufficiently at this voltage, which leads to the failure of the solvent to evaporate completely, resulting in the spinning defects described above [41]. When the voltage was further increased to 18 kV, the Taylor cone angle was observed to become smaller and jitter during the spinning process, and its microscopic morphology is shown in Figure 2G. Figure 2H,I shows the microscopic morphology under different flow rate conditions. Under the condition of 0.8 mL/h, the interruption of the Taylor cone due to insufficient solution was observed during the spinning process. While increasing to 1.2 mL/h, the droplets at the needle could not be stretched to the Taylor cone in time, resulting in droplet falling. Both sets of samples had larger diameters and were unevenly distributed compared to sample A. The results showed that the droplets were not uniformly distributed.