## 3 Results and Discussion
### CuBTC@PET Characterization Analysis  
Figure 7 shows the XRD patterns of each fiber membrane specimen by X-ray diffraction, which is a common method to confirm the crystal structure of MOFs. Comparing the XRD patterns of PET fibers before and after swelling and recrystallization, the PET fibers after swelling are smoother compared with the original PET fibers, indicating that swelling makes the PET molecular chains less crystalline. It can be proven that the swelling and recrystallization treatment can provide carboxymethyl binding sites for Cu\({}^{2+}\) and improve  
Figure 6: SEM images of CuBTC@PET composite fibers without recrystallization post-treatment at different growth cycles: (**a**) three cycles, (**b**) five cycles, (**c**) seven cycles, (**d**) nine cycles. the density of CuBTC crystal growth due to the uniformity. PET@CuBTC composite fibers were found to be in the range of 20 = 6.61\({}^{\circ}\), 9.42\({}^{\circ}\), 11.50\({}^{\circ}\), 13.30\({}^{\circ}\), 14.55\({}^{\circ}\), 14.90\({}^{\circ}\), 16.35\({}^{\circ}\), and 17.36\({}^{\circ}\), compared with PET fibers with 20 = 18.90\({}^{\circ}\), 20.10\({}^{\circ}\), 24.01\({}^{\circ}\), 25.83\({}^{\circ}\), 29.20\({}^{\circ}\), 35.13\({}^{\circ}\), and 39.09\({}^{\circ}\). They also showed new diffraction peaks, which corresponded to the CuBTC characteristic peaks [34], which preliminarily proved the in situ growth of CuBTC on the PET surface. Comparing the XRD patterns of different growth cycles, it can be seen that the intensity of the characteristic peaks of CuBTC increases with the growth cycle, and its diffraction peaks are strong, sharp, and symmetric at five cycles, crystallizing complete crystals with larger grains and more regular internal plasmonic arrangement, which proves that the degree of crystallinity is high under the cyclic conditions and the grains are larger, with more regular internal plasmonic arrangement. When the growth cycle reaches seven cycles, CuBTC diffraction peaks show a tendency to broaden, which may be due to the further growth of the crystal. The size increases, and the skeletons at different growth points squeeze each other, which affects the continuation of the crystallization process of CuBTC or leads to the growth of different crystals merging and the irregular arrangement of the internal plasmodesmata. The FTIR profiles of the fiber membranes at different treatment stages are shown in Figure 8, where PET functional groups can be determined by specific peaks, such as terephthalate C=O at 1711 cm\({}^{-1}\); asymmetric vibrational -C-C-O- at 1238 cm\({}^{-1}\); stretching vibrational -O-C-C- at 1092 cm\({}^{-1}\); and -CH- at 728 cm\({}^{-1}\)[44]. By comparing the absorption peaks before and after post-treatment, it can be determined that there is no NMP residue in the fiber, and the PET molecular chain structure is maintained. The coordination of the ligand BTC and Cu\({}^{2+}\) in CuBTC can be determined by the following peaks: COO-asymmetric vibration at 1644 cm\({}^{-1}\); COO- symmetric vibration at 1372 cm\({}^{-1}\); and -CH- aromatic out-of-plane vibration at 728 cm\({}^{-1}\). It can be initially determined that the functional structure of CuBTC has appeared in PET@CuBTC fibers, Cu\({}^{2+}\) is bonded to PET fibers mainly through the carboxyl group at both ends of the PET molecular chain, the intensity of the absorption peaks is weakened with the observation of the C=O stretching vibration at 1007 cm\({}^{-1}\) and 1711 cm\({}^{-1}\), and the C=O bonding is weakened with the growth of CuBTC occupying the -COOH group at the ends of the PET molecular chain. The intensity of the absorption peak is weakened, and it can be determined that the Cu\({}^{2+}\) is attached to the PET by bonding. Comparing the PET@CuBTC fibers before and after hydrophobic modification,  
Figure 7: XRD patterns of different fiber membranes. the FTIR spectra of PET@CuBTC fibers were unchanged, and it can be determined that the POTS hydrophobically modified coating did not change the functional group structure of PET and CuBTC.