## 3 Results and Discussion
### Batch Adsorption Experiments
As shown in Figure 6d, the maximum adsorption capacity of the SiPMA-TEPA adsorbent exceeded 198.95 mg/g. The SiPMA-TEPA adsorbent with the longest polyamine chain exhibited the highest adsorption capacity, consistent with the findings of [PERSON]'s study [34]. The adsorption capacity of the SAER adsorbent with the same polyamine group was 124 mg/g [30; 40]. Adsorption isotherm experiments were conducted to elucidate the uranium adsorption mechanism of SiPMA-TEPA. The detailed experimental procedures are described in Section S2 of the Supplementary Materials. The saturation U(VI)-adsorption capacity of SiPMA-TEPA is illustrated in Figure S3. The fitting results of the Langmuir model (Equation (S3)) [12] and the Freundlich model (Equation (S4)) [41] are shown in Table S2. The \(R^{2}\) value for the Langmuir model was higher than that for the Freundlich model, indicating that the adsorption process aligned with the Langmuir model, which represents a monolayer chemisorption process. Interfering ions in environmental water predominantly include anions such as Cl\({}^{-}\), NO\({}_{3}\)\({}^{-}\), and SO\({}_{4}\)\({}^{2-}\) and cations such as Na\({}^{+}\), K\({}^{+}\), Ca\({}^{2+}\), and Mg\({}^{2+}\). To compare the adsorption selectivity of the three polyamine resins, experiments were designed using salts with concentrations ranging from 0 mM to 100 mM. The three types of polyamine resins were reacted in these three salts (NaCl, KNO\({}_{3}\), and Na\({}_{2}\)SO\({}_{4}\)) with different concentrations. The results are shown in Figure 7. As the number of interfering ions in the solution increased, the interfering ions competed with UO\({}_{2}\)(CO\({}_{3}\))\({}_{2}\)\({}^{2-}\) or UO\({}_{2}\)(CO\({}_{3}\))\({}_{3}\)\({}^{4-}\) for adsorption with the protonated polyamine resin. The adsorption selectivity of the three polyamine resins for uranium remained high at a 100 mM salt concentration. Specifically, the uranium adsorption efficiency of all three polyamine adsorbents exceeded 90% in the presence of 100 mM NaCl or KNO\({}_{3}\) and surpassed 80% in the presence of 100 mM Na\({}_{2}\)SO\({}_{4}\). SiPMA-DETA, with the shortest polyamine chain, exhibited a higher selectivity for uranium than the other two polyamine resins. The uranium adsorption efficiency of SiPMA-DETA reached 83% in 100 mM Na\({}_{2}\)SO\({}_{4}\) \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Adsorbents** & **Pseudo-First-Order Kinetic Model** & \multicolumn{3}{c}{**Pseudo-Second-Order Kinetic Model**} & \multicolumn{3}{c}{\(\mathbf{Q_{e,exp}}\) **(mg/g)**} \\ \hline  & \(K_{1}\) & \(Q_{e}\) & \(R^{2}\) & \(K_{2}\) & \(Q_{e}\) & \(R^{2}\) & \\ \hline SiPMA-DETA & 0.71 & 5.26 & 0.999 & 0.45 & 5.33 & 0.999 & 5.26 \\ SiPMA-TETA & 0.62 & 4.94 & 0.998 & 0.34 & 5.03 & 0.997 & 4.962 \\ SiPMA-TEPA & 0.55 & 4.64 & 0.995 & 0.27 & 4.76 & 0.999 & 4.681 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters obtained by fitting the data with the pseudo-first-order and pseudo-second-order models. likely owing to the relatively higher content of primary amines in SiPMA-DETA, which enhanced selectivity [34]. As shown in Figure 8, the adsorption efficiencies of the three polyamine resins were almost unchanged with an increase in the MgCl\({}_{2}\) concentration to 5 mM, while the removal efficiencies of the three resins decreased with an increase in the CaCl\({}_{2}\) concentration to 5 mM, which corresponded to the average concentration of Ca\({}^{2+}\) in groundwater. The decrease in the removal efficiency of the resins was due to the tendency of Ca\({}^{2+}\) to combine with UO\({}_{2}\)(CO\({}_{3}\))\({}_{3}\)\({}^{4-}\) to produce a neutral molecule, Ca\({}_{2}\)UO\({}_{2}\)(CO\({}_{3}\))\({}_{3}\)[30; 42]. The removal efficiency of uranium remained around 90% in 5 mM CaCl\({}_{2}\) or MgCl\({}_{2}\), demonstrating the practical application potential of SiPMANs. In summary, the SiPMA-TEPA resin demonstrated superior overall adsorption performance and was selected for further study.