## 3 Results and Discussion
### Batch Adsorption Experiments  
As shown in Figure 6a, all three polyamine adsorbents were highly effective in removing uranium from aqueous solutions at pH 4-10, with particularly high efficiency at pH 5-9, where the removal efficiency remained nearly constant at -90%. As the H\({}^{+}\) concentration in the solution increased, the nitrogen-containing functional groups on the polyamine resin ligands became more easily protonated. However, the chemical form of uranium gradually converted from UO\({}_{2}\) (CO\({}_{3}\))\({}^{4-}\) to UO\({}_{2}\)\({}^{2+}\)[30], which is not conducive to ion exchange. This resulted in a decrease in adsorption efficiency, particularly at pH 4, where the decrease was most pronounced. As shown in Figure 6b, the polyamine adsorbents hardly adsorbed uranium when the HNO\({}_{3}\) concentration exceeded 0.1 M. As fewer H\({}^{+}\) ions were present in the solution, the nitrogen-containing functional groups on the polyamine resin ligands were less likely to be protonated, which hindered ion exchange. Consequently, the adsorption efficiency of the polyamine resins for uranium decreased, especially at pH 10. The pH of environmental water systems varies owing to regional differences, with an overall range \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Materials**} & **BET Surface Area** & **Pore Volume** & **Pore Size** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(nm)** \\ \hline SiO\({}_{2}\) & 74.59 & 0.76 & 56.08 \\ SiPMA-DETA & 48.38 & 0.25 & 23.05 \\ SiPMA-TETA & 46.86 & 0.59 & 23.77 \\ SiPMA-TETA & 46.42 & 0.61 & 52.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: BET results for SiO\({}_{2}\) and SiPMANs obtained via nitrogen adsorption. Figure 4: N\({}_{2}\)-adsorption–desorption isotherms (**a**) and pore size distributions (**b**) of SiO\({}_{2}\) and SiPMANs. of 6-8 [30]. This indicates that SiPMANs are widely applicable to diverse environmental water conditions. Figure 5: FT-IR spectra of SiO\({}_{2}\), SiPMA, and SiPMANs. Figure 6: Effect of pH on the uranium removal efficiency **(a)**; effects of the nitric acid concentration on the uranium removal efficiency **(b)**; plots of the pseudo-first-order and pseudo-second-order kinetic models for uranium adsorption **(c)**; and amount of uranium adsorbed as a function of the liquid-to-solid ratio **(d)** (C\({}_{0}\)(NaHCO\({}_{3}\)) = 3 mmol/L, initial pH 7 \(\pm\) 0.05, **(a)** C\({}_{0}\)(U) \(\approx\) 1 mg/L, \(t\) = 24 h, \(m\)/\(v\): 0.05 g/30 mL; **(b)** C\({}_{0}\)(U) \(\approx\) 10 mg/L, \(t\) = 2 h; **(c)** C\({}_{0}\)(U) \(\approx\) 10 mg/L; and **(d)** C\({}_{0}\)(U) \(\approx\) 50 mg/L, \(t\) = 2 h). The adsorption equilibrium time is a crucial performance indicator for ion exchange resins. Figure 6c illustrates the effect of the reaction time on uranium adsorption. Adsorption rapidly increased within the first 5 min, and equilibrium was reached in less than 10 min. This rapid equilibrium was due to the SiPMAN resins having a larger specific surface area and pore size, which facilitated the entry of uranium. The experimental data were fitted using the pseudo-first-order kinetic model (Equation (S1)) [38] and the pseudo-second-order kinetic model (Equation (S2)) [36] to investigate the adsorption mechanism. The fitting results are shown in Table 2.  
According to the \(R^{2}\) values in Table 2, the pseudo-second-order kinetic model was more suitable for describing the adsorption mechanism than the pseudo-first-order kinetic model, indicating that the adsorption of uranium onto SiPMA-TEPA was chemisorptive [39]. The saturated adsorption capacity of a resin is crucial for its practical application. This capacity is generally determined from the adsorption isotherm. However, at pH levels close to 7, highly concentrated uranium can hydrolyze and precipitate, which can complicate the measurement of the adsorption capacity [40]. Thus, a solid-to-liquid ratio experiment was conducted to investigate the maximum adsorption capacity of the resin.