# Carbon Spheres as CO\({}_{2}\) Sorbents
## 3 Results and Discussion
### Surface Chemistry  
The surface composition of materials was analyzed by X-ray Photoelectron Spectroscopy (XPS). The survey spectra acquired for all analyzed samples are shown in Figure 3. The evaluation of the elemental composition of the surface of all samples is presented in Table 2. In all samples, carbon and oxygen was present, and potassium was observed in samples prepared with potassium oxalate. Figure 2: (**a**) Size distribution of the reference sample. (**b**) Size distributions of the samples with lower activator content (7/1). (**c**) Size distribution of the samples with higher content of the activator (9/1). (**d**) Size distribution of the samples modified with EDA only. (**e**) Size distribution of the samples modified with EDA and activator. The highest carbon content was observed for the pure carbon material (RF_700); oxygen constitutes only 3% of the surface atoms. The surface of the samples prepared with EDA only also contained a relatively small number of oxygen atoms (approximately 4%), however those surfaces also contained about 4% of nitrogen atoms. The presence of potassium in the internal structure of the material is associated with an increased concentration of oxygen atoms. The more potassium observed in the material, the higher the concentration of oxygen observed, as residual potassium atoms were bound with oxygen. In general, when the carbonization temperature was increased to 800 \({}^{\circ}\)C, this resulted in a lower oxygen concentration than that observed for samples carbonized at 600 \({}^{\circ}\)C. There is noticeably more potassium retained on the surface of the samples modified by both potassium oxalate and EDA in comparison to materials modified by potassium oxalate only. A possible explanation for this is that a reaction of potassium with amine groups occurred. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **C** & **O** & **N** & **K** \\ \cline{2-5}  & & & **at. \%** & \\ \hline
**RF\_700** & **96** & **3** & \(\sim\)1 & - \\ \hline RF\_7\_1\_600 & 88 & 11 & \(<\)1 & \(\sim\)1 \\ \hline RF\_7\_1\_800 & 92 & 7 & \(<\)1 & \(\sim\)1 \\ \hline RF\_7\_1\_EDA600 & 87 & 8 & 3 & \(\sim\)2 \\ \hline RF\_7\_1\_EDA800 & 88 & 9 & \(<\)1 & \(\sim\)3 \\ \hline RF\_9\_1\_600 & 76 & 18 & \(\sim\)2 & \(\sim\)4 \\ \hline RF\_9\_1\_800 & 85 & 11 & \(<\)1 & \(\sim\)3 \\ \hline RF\_EDA600 & 92 & 4 & \(\sim\)4 & - \\ \hline RF\_EDA800 & 93 & 3 & \(\sim\)4 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Elemental composition of the surface of the samples. Figure 3: X-ray Photoelectron Spectroscopy (XPS) survey spectra. The analysis of high-resolution XPS data brings a more detailed view of the chemistry of the surface of the studied materials. In Figure 4, the spectral region of binding energy between 280 eV and 300 eV is displayed for two samples of carbon spheres obtained with the weight ratio potassium: carbon of 9:1 (RF_9\(1\)600 and RF_9\(1\)800). This region contains the spectrum components originating from C 1s and K 2p electrons. The peak maximum of K 2p\({}_{3/2}\) is located at 293 eV and it is accompanied with a K 2p\({}_{1/2}\) spin-orbit component at 295 eV. The peak maximum of XPS C 1s spectrum is located at 284.4 eV. This energy is characteristic for highly graphitized carbon materials. However, a distinctive shoulder at about 288 eV is present in the spectrum for both samples, though more prominent on the sample carbonized at 600 \({}^{\circ}\)C. This position is usually ascribed to the general group of carbon moieties containing O-C=O bindings. The intensity of the spectra is normalized in respect to the intensity of the main peak of carbon. It can be pointed out that the relative intensity of lines corresponding with potassium atoms as well as carbon atoms in O-C=O bindings decreases in comparison to C-C bonds, reflected by XPS C 1s peak at 284.4 eV. This shows that increased carbonization temperature results in a partial depletion of potassium atoms from the surface as well as a decomposition of a part of C-O bonds.