# Preparation and Physicochemical Properties of Tannin-Imobilized Membrane Adsorbent
## 4 Conclusions  
Typical polyamide, polyvinylidene fluoride, and cellulose microporous filter membranes were selected as basic materials using different immobilizing methods to prepare tannin-immobilized membranes: PA-BWT, PVDF-BWT, CELL-BWT, and PA-AA-BWT. The tannin grafting degrees of M-TANs prepared by different methods are different: the PA-BWT had the maximum grafting degree, followed by PA-AA-BWT and PVDF-BWT, and the minimum grafting degree belonged to CELL-BWT. The contact angle of the surface water proves that the introduction of tannins rich in phenolic hydroxyl groups improved the hydrophilicity of the original membrane, and the higher hydrophilicity resulted in a greater water flux. The adsorption performance studies show that PA-BWT had the largest adsorption capacity for UO\({}_{2}\)[24]. The PA-BWT exhibited a maximal adsorption capacity (0.4 mmol/g) at pH 5.0 and 333 K with an initial U(VI) concentration of 2 mmol/L. In addition, the adsorption isothermal and kinetic data were well fitted by the Langmuir equation and the Elovich model, respectively. The PA-BWT, PVDF-BWT, and PA-AA-BWT prepared by the covalent cross-linking method had good stability under different environmental conditions; thus, the membrane structure will not be destroyed, and the tannins on the membrane will not easily fall off. Therefore, PA-BWT exhibits a great potential in practical application for U(VI) removal from aqueous solutions as a low-cost, highly effective, and reusable adsorbent. The following are available online at [[https://www.mdpi.com/article/10.3390/appp11209684/s1](https://www.mdpi.com/article/10.3390/appp11209684/s1)]([https://www.mdpi.com/article/10.3390/appp11209684/s1](https://www.mdpi.com/article/10.3390/appp11209684/s1)). Schematic S1: Schematic illustration showing the preparation of PA-BWT, Schematic S2: Schematic illustration showing the preparation of PA-AA-BWT, Schematic S3:  
Figure 6: Water flux and adsorption capacity of different M-TANs before and after long-term shaking and soaking at (**a**,**b**) different temperatures and (**c**,**d**) pH. Schematic illustration showing the preparation of PVDF-BWT, Schematic S4: Schematic illustration showing the preparation of CELL-BWT, Figure S1: The FTIR spectra of (a)PA and PA-BWT, (b) PA and PA-AA-BWT, (c) PVDF and PVDF-BWT, (d) CELL and CELL-BWT, Figure S2: Adsorption capacity of UO\({}_{2}\)\({}^{2+}\) on different M-TANs: the initial concentration of the UO\({}_{2}\)\({}^{2+}\) solution is 1 mmol L\({}^{-1}\), the pH is 5.0, and the adsorption time is 24 h, Figure S3: Adsorption kinetics regression by the Weber-Morris model: q\({}_{t}\) = k\({}_{tp}\)t\({}^{1/2}\) + C, where \(q_{t}\) (mmol/g) are the adsorption capacity of UO\({}_{2}\)\({}^{2+}\) at time \(t\), k\({}_{tp}\) is Internal diffusion rate constant and C is a constant of the surface boundary layer thickness of the adsorbed material, Figure S4: Digital photos of different M-TAN before and after long-term shaking and soaking at different temperatures (a) 20\({}^{\circ}\)C, (b) 50\({}^{\circ}\)C, and pH (c) pH=2, (d) pH=9. Conceptualization, W.L., X.Y. and J.C. ([PERSON]); Data curation, W.L. ; Formal analysis, H.L. ; Funding acquisition, X.Y. ; Investigation, Z.W. ; Methodology, W.L. and X.Y. ; Project administration, X.Y. ; Software, H.L. ; Validation, Z.W., J.C. ([PERSON]) and R.C. ; Visualization, W.L. and X.Y. ; Writing--original draft, W.L. ; Writing--review & editing, W.L., X.Y. and J.C. ([PERSON]) All authors have read and agreed to the published version of the manuscript. This research was financially supported by the National Natural Science Foundation of China (No. 22008035), the Fujian Industry-University-Research Project (No. 2019H6008), the Natural Fujian Science Foundation National (No. 2020J05131), the Science and Technology Project of Fujian Educational Committee (No. JAT190053), the Fuzhou University Testing Fund of precious 23. apparatus (No. 2020T009), and the Research Initiation Funding of Fuzhou University (No. GXRC-19060).