# Carbon Dioxide Adsorption on Carbon Nanofibers with Different Porous Structures
## 3 Results and Discussion
### XPS Data  
PAN is characterized with the C \(\equiv\) N group. In order to understand the change of nitrogen-containing functional groups undergoing subsequent electrospinning, stabilization, carbonization, and activation processes, XPS was conducted to explore the surface elemental compositions and their chemical states. The XPS survey scan spectra of the samples indicated that the major peaks were due to the C 1s, N 1s, and O 1s photoelectrons. Figure 5 shows the atomic ratios of C 1s, N 1s, and O 1s of the samples. The atomic ratio of N 1s followed the order PANp > PANf > PANh15 > PANh12, which indicated that a larger amount of nitrogen enabled the loss of the hollow nanofibers in the manufacture processes.  
The curve-fitting for the high resolution XPS N 1s spectra [38; 39; 40] for all the samples is shown in Figure 6. The N 1s spectra were decomposed into, at most, seven identified components. Table 2 displays the percentages of nitrogen-containing functional groups. The peak at 395.7 eV was the aromatic N-times; the peak at 398.4 eV represented the pyridine-type N; the peak at 400.1 eV was the pyrrole or pyridine; the peak at 401.2 eV showed the quarternary N; the peak at 402.4 eV indicated the pyridine-N oxides; and the  
Figure 4: The ratios of surface areas and pore volumes obtained from N\({}_{2}\) adsorption–desorption data at \(-\)196 \({}^{\circ}\)C for all samples.  
Figure 5: The atomic ratios of C 1s, N 1s, and O 1s obtained from the X-ray photoelectron spectroscopy (XPS) of the samples.  
peak at 404 eV was the shake-up satellites. The contribution of chemisorbed NO\({}_{2}\) was assigned at 405 eV. PANf and PANh15 had a higher percentage of the pyrrole or pyridine (400.1 eV) and pyridine-type N (398.4 eV), while the pyridine-type N (398.4 eV) and the quarternary N (401.2 eV) were predominant on PANh12 and PANp. In summary, PANh15 had the highest percentage of pyrrole or pyridine of the five-member or six-member rings, and the pyridine-type N groups of the six-member rings were the primary functional groups on the others. In addition, PANh12 showed a higher percentage of the quarternary N and pyridine-N oxides in comparison with the others.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{6}{c}{**Binding Energy (eV)**} \\ \cline{2-7}  & **395.7** & **398.4** & **400.1** & **401.2** & **402.4** & **404** & **405** \\ \cline{2-7}  & \begin{tabular}{c} **Aromatic** \\ **N-imines** \\ \end{tabular} & \begin{tabular}{c} **Pyridine** \\ **-Type N** \\ \end{tabular} & \begin{tabular}{c} **Pyrole or** \\ **-Type N** \\ \end{tabular} & \begin{tabular}{c} **Quaternary** \\ **N** \\ \end{tabular} & \begin{tabular}{c} **Pyridine-** \\ **N** **oxides** \\ \end{tabular} & \
\begin{tabular}{c} **Shake-Up** \\ **Satellites** \\ \end{tabular} &
\begin{tabular}{c} **NO\({}_{2}\)** \\ **NO\({}_{2}\)** \\ \end{tabular} \\ \hline PANf & — & 21.8 & 20.5 & 18.4 & 10.3 & 1.2 & 27.8 \\ \hline PANh15 & 8.0 & 20.6 & 29.1 & 16.7 & 11.9 & — & 13.7 \\ \hline PANh12 & 0.3 & 37.2 & 7.7 & 22.4 & 14.2 & — & 18.2 \\ \hline PANp & 6.2 & 32.2 & 15.3 & 19.5 & 9.4 & 2.8 & 14.7 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of the fits of the XPS N\({}_{1\mathrm{s}}\) region, values shown at. % of total intensity.  
Figure 6: Results of the fits of the high resolution X-ray photoelectron spectroscopy (XPS) N 1s region: (**a**) PANf; (**b**) PANh15; (**c**) PANh12; (**d**) PANp. The values were given in atomic ratio (%) of total intensity.