# Preparation and Physicochemical Properties of Tannin-Imobilized Membrane Adsorbent
## 3 Results and Discussion
The characteristic peaks of C 1s and F 1s at binding energies of 285.08 eV and 684.8 eV appeared in both PVDF  
Figure 1: The tannin loading capacity of the tannin-immobilized membranes: PA-BWT, PA-AA-BWT, PVDF-BWT, and CELL-BWT. Figure 2: FESEM images of (**a,b**) PA and PA-BWT, (**c,d**) PA-AA and PA-AA-BWT, (**e,f**) PVDF and PVDF-BWT, and (**g,h**) CELL and CELL-BWT. and PVDF-BWT. However, the difference is that the characteristic peak of O 1s at a binding energy of 531.1 eV newly appeared in PVDF-BWT, and the peak intensity of F is decreased, while the peak intensity of C 1s increased. This is due to the introduction of tannins containing multiple benzene rings and phenolic hydroxyl groups, thereby introducing the O element and increasing the C 1s content on the surface of PVDF-BWT. Further analysis of the O 1s spectrum (as shown in Figure 3g,h) indicates that the intensity of the O 1s peak in the PVDF spectrum was extremely low, which may have been caused by impurities on the surface of the PVDF membrane. In contrast, the O 1s peak intensity of PVDF-BWT was greatly improved, and could be divided into two peaks, C=O and C-O, with binding energies of 531.6 eV and 532.5 eV, respectively, which were caused by the immobilizing of tannins. The XPS spectrum of PA-AA-BWT were similar to those of PA-BWT (Figure 3i,j). The N 1s peak intensity of PA-AA-BWT was reduced after the tannin was immobilized by the esterification reaction. Compared with PA-BWT, the content of C 1s and O 1s in PA-AA-BWT changed. The content of O 1s in PA-AA-BWT increased and was higher than that of C 1s due to the introduction of the carboxyl group in the esterification reaction of methacrylate. Figure 3k,l shows the XPS spectra of CELL and its tannin-immobilized membrane CELL-BWT. Both CELL and CELL-BWT contain C and O elements. However, in Figure 3l, after immobilizing tannin, the peak intensity of O 1s decreased and the peak intensity of C 1s increased. This is due to the introduction of tannins with multiple benzene rings, thereby increasing the C 1s content on the surface of CELL-BWT. The FTIR spectra also confirmed the successful synthesis of four M-Tans (Figure S1). Figure 3: High resolution XPS spectra and O 1s spectra of (**a–d**) PA and PA-BWT, (**e–h**) PVDF and PVDF-BWT, (**i,j**) PA and PA-AA-BWT, and (**k,l**) CELL and CELL-BWT. The hydrophilicity of the microporous membrane and the M-TANs were evaluated by testing the water contact angle of the surface. Figure 4a shows the water contact angles of various membranes and M-TANs. As shown in Figure 4a, the hydrophilicity of the PA was significantly enhanced after immobilizing the tannin, and the water contact angle was reduced from the original 88.5\({}^{\circ}\) to 70.1\({}^{\circ}\). This is because after the cross-linking reaction between the 6,8 positions on the tannin A ring and the amino group of the PA, the unreacted phenolic hydroxyl group on the tannin is exposed to the surface of the M-TANs, and the phenolic hydroxyl group is a strong hydrophilic group [26]. Therefore, the hydrophilicity of PA-BWT was enhanced. The hydrophilicity of PA-AA-BWT was also enhanced, and the water contact angle was reduced from the original 88.5\({}^{\circ}\) to 72.5\({}^{\circ}\). However, compared with PA-BWT, the hydrophilicity of PA-AA-BWT was not as strong due to a smaller tannin grafting degree. PVDF membrane is a hydrophobic microporous membrane with a water contact angle of 110.4\({}^{\circ}\), but the hydrophobicity of PVDF-BWT immobilized with tannin obviously changed greatly, and the water contact angle directly dropped to 85.2\({}^{\circ}\). It changed from a hydrophobic membrane to a hydrophilic membrane, which is also caused by the tannins rich in hydrophilic phenolic hydroxyl groups. The CELL membrane itself is a hydrophilic membrane with a water contact angle of 81.2\({}^{\circ}\). After the tannin was immobilized by the dip coating method, the hydrophilicity of CELL-BWT was slightly reduced, and the contact angle increased to 84.2\({}^{\circ}\).