## 3 Results and Discussion
### Filtration Performance Analysis  
Figure 13 shows the N\({}_{2}\) adsorption-desorption isotherms; compared with the classification of gas adsorption isotherms defined by the International Union of Theoretical and Applied Sciences (IUPAC), it can be seen that the N\({}_{2}\) adsorption-desorption isotherms of PET fibers is a type III curve, and its specific surface area is 1.175 m\({}^{2}\)/g, which indicates that there is no microporous structure in the PET fibers. The N\({}_{2}\) adsorption-desorption isotherms of the CuBTC powders show a typical type I shape of microporous materials with a specific surface area of 600.639 m\({}^{2}\)/g, which is consistent with the data published by [PERSON] et al. [34]. The N\({}_{2}\) adsorption-desorption isotherm of the solubilized recrystallized PET was determined as a type IV shape with an H2-type mesoporous hysteresis loop and a specific surface area of 3.093 m\({}^{2}\)/g, indicating the presence of a large number of irregular mesopores on top of the composite fibers. The N\({}_{2}\) adsorption-desorption isotherm of CuBTC@PET was determined as a type IV shape with an H2-type mesoporous hysteresis loop and a specific surface area of 10.524 m\({}^{2}\)/g, suggesting that CuBTC@PET is a typical microporous material. The results showed that the micropores and mesopores of CuBTC@PET fibers were derived from the structures of CuBTC and solution-recrystallized PET, respectively. In summary, the  
Figure 12: Thermogravimetric-differential scanning calorimetry for different samples. dissolution-recrystallized PET fibers showed a mesoporous structure in the N\({}_{2}\) adsorption-desorption isotherm, while the specific surface density of CuBTC@PET fibers after CuBTC in situ growth decreased compared to that of CuBTC powder but increased substantially compared to that of PET fibers and dissolution-recrystallized PET fibers, which was about 10 times of that of PET fibers and 3.5 times of that of dissolution-recrystallized PET fibers. It is about 10 times that of PET fiber and 3.5 times of solubilized recrystallized PET fiber. In this paper, the fiber membrane thickness was too low for accurate measurement, so it was determined by weighing the calculated fiber membrane g/m\({}^{2}\) with an electronic balance. The thickness of the fiber membrane is an important factor affecting its filtration efficiency. When the fiber membrane is thicker, the pore path in the filtration medium is more complex, and it can intercept small particles more effectively, thus improving the filtration efficiency, but overly thick fibers will also increase the resistance to fluid flow, resulting in a decline in filtration performance. By optimizing the thickness of the fiber membrane, a higher filtration efficiency can be achieved while maintaining a lower filtration resistance, achieving the best balance of filtration performance. Figure 14a shows the control of fiber film thickness by spinning time. The filtration efficiency of fiber membranes with different thicknesses is improved with the increase in particle size, and the change curves are similar. As the thickness of the fiber membrane increased from 2.4 g/m\({}^{2}\) to 5.4 g/m\({}^{2}\), the filtration efficiency was significantly improved, but when the thickness of the fiber membrane increased to 8.3 g/m\({}^{2}\), the filtration efficiency was not significantly improved, so 5.4 g/m\({}^{2}\) was selected for the subsequent experiments, and the filtration efficiency was measured. By observing Figure 14b, the filtration efficiency of the PET fibers after the swelling and recrystallization treatment was significantly improved compared to that of the initial PET fibers. This may be attributed to the porous structure and high specific surface area of the fiber surface after swelling.