## 3 Results and Discussion
### Physicochemical Properties of HMS-SO\({}_{3}\)H and NRHMS-SO\({}_{3}\)H
(**B**) Wide-scan XPS spectrum, and core-level, high-resolution (**C**) O1s and (**D**) S2p XPS spectra of HMS-SO\({}_{3}\)H (0.4). The wide-scan and core-level high-resolution XPS spectra of other NRHMS-SO\({}_{3}\)H samples are shown in Figures S2-S7 (SM). Figure 2: Representative (**A**) ATR-FTIR spectra of NRHMS-SO\({}_{3}\)H with different MPTMS loading levels. (**B**) Wide-scan XPS spectrum, and core-level, high-resolution (**C**) O1s and (**D**) S2p XPS spectra of NRHMS-SO\({}_{3}\)H (0.4). The wide-scan and core-level high-resolution XPS spectra of other NRHMS-SO\({}_{3}\)H samples are shown in Figures S8–S13 (SM). The TG and DTA curves of the HMS-SO\({}_{3}\)H and NRHMS-SO\({}_{3}\)H series are compared in Figure 5A,B, respectively. For the HMS-SO\({}_{3}\)H series, all samples exhibited three-step weight loss. First, a weak endothermic peak observed between 50 \({}^{\circ}\)C and 150 \({}^{\circ}\)C was attributed to the desorption of physisorbed water and ethanol from the material surface. The second instance of weight loss was located in the range of 250-450 \({}^{\circ}\)C corresponding to the decomposition of the mercaptopropyl group and the remnant ethoxy group [37]. The final exothermic step, in the range of 450-650 \({}^{\circ}\)C, was ascribed to the decomposition of alkyl sulfonic groups, the removal of carbon residue, and the dehydroxylation of silanol groups on the material surface [38]. The remaining weight of the solid was used to calculate the silica content in the materials. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**SiO\({}_{2}\)**} & \multicolumn{1}{c}{**S**} & \multicolumn{1}{c}{**Theoretical**} & \multicolumn{1}{c}{**Total**} & \multicolumn{1}{c}{**Sulfur Species \({}^{\bullet}\)**} \\  & **Content** & **Content** & **Acidity \({}^{\circ}\)** & **Acidity \({}^{\circ}\)** & **Acidity \({}^{\circ}\)** & **(mmol/g)** \\  & \({}^{\circ}\)**(wt.\%)** & **b (wt.\%)** & **(mmol/g)** & **(mmol/g)** & **-SH** & **-SO\({}_{3}\)H** \\ \hline HMS-SO\({}_{3}\)H (0.2) & 67.8 & 7.8 & 2.45 & 0.69 & 1.87 & 0.58 \\ HMS-SO\({}_{3}\)H (0.4) & 64.4 & 10.3 & 3.22 & 0.79 & 2.36 & 0.85 \\ HMS-SO\({}_{3}\)H (0.6) & 55.4 & 12.2 & 3.80 & 0.90 & 2.64 & 1.16 \\ NRHMS-SO\({}_{3}\)H (0.2) & 62.6 & 7.1 & 2.21 & 0.62 & 1.63 & 0.58 \\ NRHMS-SO\({}_{3}\)H (0.4) & 56.0 & 8.6 & 2.68 & 0.71 & 1.95 & 0.74 \\ NRHMS-SO\({}_{3}\)H (0.6) & 54.6 & 11.4 & 3.56 & 0.80 & 2.27 & 1.29 \\ \hline \hline \end{tabular}  
* Silica content determined by TGA. \({}^{\circ}\) Sulfur content determined by CHNS analysis. \({}^{\circ}\) Calculated from the total sulfur content by assuming complete oxidation of -SH to -SO\({}_{3}\)H. \({}^{\ddagger}\) Determined from acid–base titration. \({}^{\circ}\) Total sulfur content, obtained via CHNS analysis, was divided into each species using XPS analysis.  
\end{table} 
Table 1: Chemical composition and acidity comparison of HMS-SO\({}_{3}\)H and NRHMS-SO\({}_{3}\)H.  
Figure 3: Representative (**A**) TEM of HMS-SO\({}_{3}\)H (0.4) at a magnification of 100,000\(\times\) and EDS mapping images of elements (**B**) C, (**C**) Si, and (**D**) S.  
Figure 4: Representative (**A**) TEM of NRHMS-SO\({}_{3}\)H (0.4) at a magnification of 100,000\(\times\) and EDS mapping images of elements (**B**) C, (**C**) Si, and (**D**) S.  
Figure 5: _Cont._  
The NRHMS-SO\({}_{3}\)H series provided similar weight loss profiles for the HMS-SO\({}_{3}\)H counterparts, but with a broader exothermic step at 200-450 \({}^{\circ}\)C due to the additional weight loss from the decomposition of the rubber phase. Hence, the exact amount of the NR component incorporated in the nanocomposites could not be determined [24]. To estimate the incorporated NR content of nanocomposites, non-functionalized NRHMS was analyzed as a representative material using TGA, showing 12 wt.% of NR content. Notably, NRHMS-SO\({}_{3}\)H (0.2) provided a small exothermic peak at 250 \({}^{\circ}\)C owing to the auto-oxidation of loosely entrapped NR molecules within the silica framework [28].