# Assessment of Catalyst Selectivity in Carbon-Nanotube Silylesterification
## 3 Results
### Diazonium-Mediated Modification
The MWNT-C(O)-CH\({}_{3}\) sample contained larger C=O (1.3%, 286.9 eV) and C(O)-O (1.2%, 289.2 eV) components. This confirmed the presence of a highly oxidized functional group (a ketone) on the MWNT surface. An increase in Csp\({}^{3}\) contribution was observed due to the presence of a methyl group on the ketone molecule. CNTs modified with an -O-CH\({}_{3}\) side chain displayed high C-O contribution (5.6%, 285.8 eV), which is characteristic of ether. HSPs are a means to describe interactions between a solute and a solvent. Each compound is described by three parameters: A dispersion parameter, accounting for dispersion forces (\(\delta_{\rm d}\)); a polar parameter (\(\delta_{\rm p}\)), accounting for dipole-dipole interactions; and a hydrogen-bond parameter (\(\delta_{\rm h}\)). A solute and solvent that are characterized by close parameters are compatible and thus soluble in each other. By contrast, compounds with largely different parameters are immiscible. Therefore, it is  
Figure 4: High-resolution C1s spectra of the six samples of diazonium-modified CNTs with various components described in Table 2.  
possible to determine HSPs of an unknown compound by testing its solubility in several solvents with known HSPs. Some solvents appear to be \"good solvents.\" On a tridimensional plot (using the three parameters as axes), \"good solvents\" are encompassed by a sphere with a center corresponding to the solubility of the compound with unknown HSPs. HSP theory [20] was proven to be applicable in the case of CNTs (crude and functionalized), and could therefore be used to characterize functionalized CNTs. Modified CNTs should be characterized by different HSPs from those of the starting material, and each functionalization produces CNTs with different parameters. HSPs were determined for six modified samples (Table 4), and the corresponding solubility spheres are shown in Figure 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \(\mathbf{\delta_{\text{d}}}\) **(MPa1/2)** & \(\mathbf{\delta_{\text{p}}}\) **(MPa1/2)** & \(\mathbf{\delta_{\text{h}}}\) **(MPa1/2)** \\ \hline CNT–COOH & 17.9 & 14.5 & 7.7 \\ CNT–CH2–COOH & 18.1 & 14.4 & 8.7 \\ CNT–OH & 16.2 & 19.2 & 13.5 \\ CNT–CH2–OH & 21.1 & 8.4 & 14.4 \\ CNT–CO()–CH3 & 18.1 & 8.6 & 5.3 \\ CNT–O–CH3 & 17.8 & 5.1 & 7.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Hansen solubility parameters (HSPs) for six samples of diazonium-modified CNTs. Figure 5: Tridimensional representation of Hansen solubility spheres for six diazonium-modified CNT samples. Note: good solvents, blue; bad solvents, red. For CNT–OH sample, only sphere center is shown. The six modified samples exhibited HSPs (Figure 6 and Table 4) that differed from those of nonfunctionalized MWNTs (\(\delta_{\text{d}}\) = 19.7 MPa\({}^{1/2}\), \(\delta_{\text{p}}\) = 6.2 MPa\({}^{1/2}\), and \(\delta_{\text{h}}\) = 4.2 MPa\({}^{1/2}\)). COOH- and CH\({}_{2}\)-COOH-modified CNTs were characterized by similar HSPs. They showed strong polar parameters and moderate hydrogen bond parameters, which was consistent with the grafting of a carboxyl-like functional group. Comparatively, CNTs modified with MWNT-OH and MWNT-CH\({}_{2}\)-OH displayed HSPs with greater hydrogen-bond contribution but lower (at least for MWNT-OH) polar contribution, which was consistent with an alcohol-like functional group. CNTs modified with ketone and ether side chains were characterized by lower polar and hydrogen-bond parameters compared with samples functionalized with alcohol or carboxyl functional groups. As shown in Table 5, the HSPs of MWNT-C(O)-CH\({}_{3}\) and MWNT-O-CH\({}_{3}\) were consistent with the tabulated values for ketones and ethers. Ketones are characterized by a greater polar parameter than the hydrogen-bond parameter. The ether showed low polar and hydrogen-bond parameters, with \(\delta_{\text{p}}\) being lower than \(\delta_{\text{h}}\)[19].