# Assessment of Catalyst Selectivity in Carbon-Nanotube Silylesterification
## 3 Results
### Diazonium-Mediated Modification  
MWNT samples functionalized by diazonium (CNT-COOH, CNT-CH\({}_{2}\)-COOH, CNT-OH, CNT-CH\({}_{2}\)OH, CNT-C(O)-CH\({}_{3}\), and CNT-O-CH\({}_{3}\)) were characterized using X-ray photoelectron spectroscopy spectra and changes to their HSPs. In the case of characterization using XPS, difficulties were created by the fact that functionalization does not introduce a new element to the modified sample. Therefore, the fit of the C1s peak was used to assess functionalization efficacy. The C1s fit table (Table 2) was established using previously reported values [21,22] and analysis of standard samples such as those containing regraphitized MWNTs. The element composition and components of the C1s peaks for the six samples are summarized in Table 3 and Figure 2, respectively. Figure 2 shows the C1s high-resolution XPS spectra for the six samples and contributions of the various components. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Type** & **C sp\({}^{2}\) (\%)** & **C sp\({}^{3}\) (\%)** & **C-O (\%)** & **C=O(\%)** & **CO(O)-O (\%)** & **Shake-up (\%)** & **Carbide (\%)** \\ \hline Energy (eV) & 284.4 \(\pm\) 0.2 & 285.0 \(\pm\) 0.2 & 285.8 \(\pm\) 0.2 & 286.9 \(\pm\) 0.2 & 289.2 \(\pm\) 0.2 & 291.0 \(\pm\) 0.2 & 283.7 \(\pm\) 0.2 \\ \hline \end{tabular}
\end{table} 
Table 2: XPS fitting parameters of various C1s peak components. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**At.\%** & **CNT-COOH** & **CNT-CH\({}_{2}\)-COOH** & **CNT-OH** & **CNT-CH\({}_{2}\)-OH** & **CNT-C(O)-CH\({}_{3}\)** & **CNT-O-CH\({}_{3}\)** \\ \hline C & 91.3 \(\pm\) 0.3 & 85.7 \(\pm\) 0.2 & 92.6 \(\pm\) 1.1 & 88.9 \(\pm\) 0.3 & 93.9 \(\pm\) 0.2 & 92.4 \(\pm\) 0.6 \\ N & 0.9 \(\pm\) 0.4 & 6.4 \(\pm\) 0.4 & 0.5 \(\pm\) 0.5 & 2.5 \(\pm\) 0.1 & 0.1 \(\pm\) 0.1 & 0.7 \(\pm\) 0.7 \\ O & 7.7 \(\pm\) 0.1 & 7.8 \(\pm\) 0.2 & 6.9 \(\pmBoth the element composition and contributions of various components of the C1s peak were highly reproducible, as demonstrated by small standard deviations. Table 3 shows the amount of increased oxygen in the six samples after functionalization. In samples where the side chain was separated from the aromatic core by a methylene group, a noticeable nitrogen peak was seen. High-resolution spectra of the N1s peak in those samples (CNT-CH\({}_{2}\)-COOH and CNT-CH\({}_{2}\)-OH) showed an asymmetric peak at 400.0 eV. Diazonium bridges exhibited a binding energy of 398.5 eV (Figure 3, standardization using methyl orange), which was close to that of amines (399.5 eV, depending on the side chain). Therefore, the conclusion that the N1s peak originated from a diazonium bond was derived from (i) the asymmetry of the peak, which is characteristic of delocalized electrons, and (ii) the absence of a decrease in intensity after further washing, which removes adsorbed molecules. Figure 4 shows an increase in the Csp\({}^{3}\) component in all functionalized samples. This increase was consistent with diazonium-mediated functionalization, as this modification transforms sp\({}^{2}\) carbons of the CNT sidewall into Csp\({}^{3}\) carbons [23]. Figure 3: High-resolution N1s spectra for CNT-CH\({}_{2}\)–OH sample, pure 4-hydroxaniline sample, and methyl orange (diazoic compound). Figure 2: Quantity of various components of C1s peak for six diazonium-modified carbon nanotube samples. When assessing functionalization via C1s peak fitting, it was found that MWNT-COOH and MWNT-CH\({}_{2}\)-COOH samples contained a C(O)-O component (2.6% and 2.8%, respectively). Additionally, the Csp\({}^{3}\) component was larger in the CNTs functionalized with -CH\({}_{2}\)-COOH than in their -C(O)-O counterpart, which was consistent with the presence of an additional methylene group. For CNTs functionalized with -OH and -CH\({}_{2}\)-OH, the C-O component (\(285.8\pm 0.2\) eV) increased by 4.4% and 4.5%, respectively, with a larger sp\({}^{3}\) component in the case of -CH\({}_{2}\)-OH functionalization. This confirmed the grafting effectiveness for both side chains.