## 3 Results and Discussion
### Effect of Irradiation  
#### 3.7.1 Irradiation Stability and Thermal Stability of SC4A  
Irradiation stability and thermal stability are important properties of extractants for radioactive elements. Therefore, SC4A was subjected to irradiation and thermogravimetric analysis. Detailed irradiation parameters are listed in Table 4.  
Photographs of SC4A samples before and after irradiation are presented in Figure 9. SC4A was white initially, but its color changed gradually to buff when the irradiated dose was higher than \(5.0\times 10^{5}\) Gy. The IR spectra of SC4A samples irradiated under different doses are presented in Figure S6 (in Supplementary Materials). It can be seen that the IR spectra of irradiated samples B and C remained the same as that of sample A, while a weaker absorbed peak appeared in that of sample D at 1728.2 cm\({}^{-1}\) owing to the appearance of a C=O group, for which the flex vibration zone ranges from 1870 to 1650 cm\({}^{-1}\)[44], and its intensity increased at a higher irradiated dose of \(1.1\times 10^{6}\) Gy as shown in the spectrum of sample E.  
MS spectrum data are an important tool to examine the decomposition of a material. To determine whether the SC4A decomposed in the experiment conditions, samples were analyzed via ESI-MS. The MS spectra of these samples are presented in Figure S7 (in Supplementary Materials). The main molecular peaks for samples were at 847.2, 847.3, 847.3, 847.2, and 847.3, respectively, showing that there were no discernible changes in the MS spectra. This indicated that there was no group loss even under an irradiation dose of \(1.1\times 10^{6}\) Gy. TGA measurements of all samples were carried out from 50 to 600 \({}^{\circ}\)C. The results are displayed in Figure S8 (in Supplementary Materials). For un-irradiated sample A, it can be seen that at a temperature \begin{table}
\begin{tabular}{c c c} \hline \hline
**Irradiated Samples** & **Dose Rate (Gy/min)** & **Irradiation Dose (Gy)** \\ \hline A & 0 & 0 \\ B & 30 & \(1.0\times 10^{4}\) \\ C & 30 & \(1.0\times 10^{5}\) \\ D & 50 & \(5.0\times 10^{5}\) \\ E & 75 & \(1.1\times 10^{6}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Irradiation parameters of the SC4A sample. Figure 9: The photograph of SC4A samples before and after irradiation, irradiated dose: (**A**) 0 Gy; (**B**) \(1.0\times 10^{4}\) Gy; (**C**) \(1.0\times 10^{5}\) Gy; (**D**) \(5.0\times 10^{5}\) Gy; and (**E**) \(1.1\times 10^{6}\) Gy. range of 80-120 \({}^{\circ}\)C, there was 4% weight loss due to evaporation of water. The main stage on thermal degradation curves from 400 to 420 \({}^{\circ}\)C was assigned to the loss of the _p-tert_-butyl functional groups and the SO\({}_{2}\) groups of SC4A. In this stage, the weight loss of the sample was approximately 60%, which was close to the theoretical value of 57% of the molecular weight of the _p-tert_-butyl and SO\({}_{2}\) groups. The second stage from 420 to 550 \({}^{\circ}\)C was due to the breakage of the SC4A rings. The weight loss curves of irradiated samples were similar to that of sample A with the exception of sample E. It was irradiated at 1.1 \(\times\) 10\({}^{6}\) Gy, which probably resulted in structural changes of trace impurities, and thus its residuals were more abundant than those of other samples. The SC4A samples before and after irradiation were also evaluated by UV-visible spectroscopy and \({}^{1}\)H-NMR spectrum, and the results are presented in Figures S9 and S10, respectively (in Supplementary Materials). In the UV/vis spectroscopy, all the samples exhibited an absorption band with absorption maxima at 245 and 309 nm. No notable changes were observed in the UV/vis spectroscopy and \({}^{1}\)H-NMR spectrum. Based on MS, TGA, UV/vis and \({}^{1}\)H-NMR analyses, it can be concluded that the SC4A remained unchanged under an irradiation dose of 1.1 \(\times\) 10\({}^{6}\) Gy.