## 3 Results and Discussions
### Adsorption Isotherms  
The Langmuir adsorption model and Freundlich adsorption model were adopted to evaluate the adsorption capacity of PVK and PVKAP to U(VI). Further details about Langmuir and Freundlich isotherm adsorption models have been explained in the Supplementary Materials. Figure 4 and Table 2 show the specific fitting parameters, the adsorption capacity of U(VI) by PVKAP is significantly improved. Additionally, the adsorption capacity of PVKAP to U(VI) increases as the initial U(VI)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **BET Surface Area (m\({}^{2}\) g\({}^{-1}\))** & **Pore Volume (cm\({}^{3}\) g\({}^{-1}\))** & **Average Pore Size (nm)** \\ \hline PVK & 5.02 & \(4.954\times 10^{-3}\) & 4.47 \\ \hline PVKAP & 6.63 & \(7.965\times 10^{-3}\) & 5.12 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Pore structure parameters of PVK and PVKAP.  
Figure 3: (**a**) Nitrogen adsorption–desorption isotherms of PVK and PVKAP; (**b**) the thermogravimetric analysis (TGA) analysis curves of PVK and PVKAP.  
concentration increases, indicating that the initial U(VI) concentration is the main driving force for the liquid-solid phase adsorption. Furthermore, the capture capacity of PVKAP increases rapidly when the U(VI) concentration is relatively low, while the adsorption capacity increases slowly as its concentration increases to relatively high values. Thus, the efficient capture of U(VI) by PVKAP could be ascribed to surface complexation rather than U(VI) precipitation [46].  
Simultaneously, the fitting results of the Langmuir adsorption model show that the maximum adsorption capacities (pH = 5, \(T\) = 293 K) of PVK and PVKAP are 57.2 and 714.3 mg g\({}^{-1}\), respectively. The significantly increased adsorption capacity of PVKAP could be attributed to the increased adsorption sites introduced by copolymerization on the surface of PVK, which is in accord with the results of FTIR spectroscopy. In addition, the Langmuir adsorption model could be better to describe the adsorption process of U(VI) on PVKAP compared to the Freundlich adsorption model, which indicates that the active adsorption sites on PVKAP are uniformly distributed, and the adsorption process is a single layer adsorption process.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Adsorbate** & \(T\) **(K)** & \(q_{\text{e}}\) **(mg g\({}^{-1}\))** &
\begin{tabular}{c} **Langmuir \(K_{\text{L}}\)** \\ **(L mg\({}^{-1}\))** \\ \end{tabular} & \(R^{2}\) & \(K_{\text{F}}\) **(mg\({}^{1+n}\) L\({}^{n}\) g\({}^{-1}\))** & **Freundlich \(n\)** & \(R^{2}\) \\ \hline PVK & 293 & 57.2 & 0.03 & 0.991 & 3.2 & 0.60 & 0.971 \\ \hline PVKAP & 293 & 714.3 & 0.42 & 0.995 & 257.5 & 0.34 & 0.971 \\ \hline PVKAP & 313 & 770.2 & 0.82 & 0.994 & 362.3 & 0.29 & 0.950 \\ \hline PVKAP & 333 & 853.7 & 1.03 & 0.994 & 428.8 & 0.29 & 0.952 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Isotherms parameters of Langmuir and Freundlich for PVK and PVKAP.  
Figure 4: **(a)** Experimental equilibrium adsorption data of PVK and PVKAP under the condition of m/V = 0.1 g L\({}^{-1}\), C U(VI)initial = 12.8–79.4 mg L\({}^{-1}\), pH = 5 and 293 K; **(b)** adsorption isotherms of Langmuir (solid line) and Freundlich (dash line) for PVKAP capturing (VI) under different temperatures; **(c)** effect of temperature on the U (VI) captured by PVKAP; **(d)** variation of ln \(K_{\text{d}}\) with T\({}^{-1}\).