## 3 Results and Discussion  
### Physicochemical Properties of HMS-SO\({}_{3}\)H and NRHMS-SO\({}_{3}\)H  
HMS-SO\({}_{3}\)H functionalization with different MPTMS loading levels was validated through the ATR-FTIR and XPS spectra, as shown in Figure 1. The wide-scan XPS spectrum of HMS-SO\({}_{3}\)H (0.4) confirmed the presence of sulfur and silica framework structures, exhibiting six characteristic bands at 284.5, 533, 233, 160, 151, and 100 eV, corresponding to C1s, O1s, S2s, S2p, Si2s, and Si2p, respectively. The chemical state of oxygen exhibited the siloxane bond (Si\(-\)O\(-\)Si) as the material core structure at 532.6 eV. Other chemical states were also seen at 531.8 and 533.9 eV, corresponding to Si\(-\)O\(-\)C of remnant ethoxy groups and Si\(-\)O\(-\)H of silanol groups, respectively [28]. In-depth ATR-FTIR spectra of the synthesized samples are illustrated in the Supplementary Material (SM) Figure S1. The bands related to sulfonic acid groups were observed in doublets at 1340 cm\({}^{-1}\) and 1315 cm\({}^{-1}\), attributed to the stretching vibration of -SO\({}_{3}\) species [29]. The band at 1360 cm\({}^{-1}\) corresponded to the S = O stretching [24]. The small band at 1300 cm\({}^{-1}\) indicated the asymmetric stretching vibration of S = O [30]. The high resolution O1s XPS spectrum affirmed the chemical state of sulfur as O = S=O moieties of sulfonic acid groups, detected at 533.0 eV [31]. Additionally, the bands corresponding to sulfonic acid species were detected from a high-resolution S2p spectrum at 166.2-170.5 eV (deconvoluted into two orbital splitting states, 2 Sp1/2 at 168.0 eV and 2 Sp3/2 at 169.2 eV) [32; 33]. However, the chemical state survey of sulfur displayed the presence of a thiol group, located between 161.8 eV and 166.2 eV (deconvoluted into two orbital splitting states, S2p1/2 at 163.6 eV and 2 Sp3/2 at 164.8 eV). This unoxidized thiol group was not observed in the ATR-FTIR spectra due to the weak signal of S\(-\)H species [34]. Notably, thiol group oxidation strongly relies on temperature [35]; hence, the total oxidation of the thiol group could not occur at 40 \({}^{\circ}\)C. Besides, thiol groups were possibly located within the sublayer of the silica framework, thus remaining in unoxidized forms [36]. The same spectroscopic techniques accessed the functional groups of NRHMS-SO\({}_{3}\)H with different loading levels of MPTMS, as shown in Figure 2. These spectra indicate that HMS-SO\({}_{3}\)H and NRHMS-SO\({}_{3}\)H exhibited similar chemical natures. The oxygen states of NRHMS-SO\({}_{3}\)H (0.4) nanocomposites were similar to those of HMS-SO\({}_{3}\)H (0.4) but different in relative concentrations (Table S1), wherein NRHMS-SO\({}_{3}\)H (0.4) possessed a higher amount of unhydrolyzed and uncondensed silica than HMS-SO\({}_{3}\)H (0.4). NR possibly hindered the formation of silica framework with functional groups, resulting in unhydrolyzed silica precursor and uncondensed silica species, thereby having less propensity to form a siloxane bond. As per the high-resolution S2p spectrum, the sample possessed both unoxidized and oxidized thiol species. The total sulfur content of the functionalized materials is summarized in Table 1. An increase in the MPTMS loading level in all cases resulted in higher sulfur content. Compared with the HMS-SO\({}_{3}\)H series, NRHMS-SO\({}_{3}\)H samples provided slightly lower sulfur content as NR hampered the formation of the silicate network, hindering the further incorporation of MPTMS into the mesostructured framework of the nanocomposite [24]. STEM-EDS was later applied to investigate the dispersion of sulfur species in the materials. As shown in Figures 3 and 4, sulfur was homogeneously distributed over the material particles for both samples, confirming that functionalization via co-condensation provided a uniform distribution of organic moieties even with NR. Figure 1: Representative (**A**) ATR-FTIR spectra of HMS-SO\({}_{3}\)H with different MPTMS loading levels.