## 3 Results and Discussion
### Adsorbents Characteristics
#### 3.1.4 Surface Chemistry of Adsorbents  
In addition to structural features such as the surface area of the adsorbent, and porosity properties, which determine the effectiveness of the process, and the transport of adsorbates, the chemistry of the surface and its affinity for potential adsorbates are specific factors in the adsorption process. In this work, X-ray photoelectron spectroscopy (XPS) was used as a quantitative technique to measure the elemental composition of the surface and to determine the bonding states of the elements. Figure 12 shows the survey scan and high-resolution spectra of mesoporous carbon surfaces (C1-C4). The details of the XPS analysis of investigated samples are presented also in Table 5.  
The XPS peaks of the main elements detected on the very top surface (1-10 nm) were labelled on the XPS spectra. In the case of mesoporous carbon materials, the O1s, O2s, C1s, Si2s, and Si2p signals were identified for all materials. Thus, the composition of the tested materials was confirmed, while a silica phase content of several percent was observed as a residue from the synthesis of carbon materials. The content of the silica phase is not high, and the intensity of the 2s and 2p peaks (the highest for sample C3) is reflected in the percentage shown in Table 5 (maximum value 4.4% for sample C3). For the adsorption process of derivatives of thiazine and triarylmethane, the most important issue is the surface chemistry and functional groups related to carbon atoms that can effectively participate in such a process. For this purpose, high-resolution XPS analysis was performed. Because this work focuses on a detailed description of the adsorption of dyes on the carbons C3 and C4, the detailed XPS analysis will also be limited here for these two materials. Two selected carbons (although the remaining carbons C1 and C3 have similar results) show similar spectrum components, and the difference mainly concerns their mutual content. The main peaks of C1s at 284.3 and 284.8 eV are attributed to the sp2 carbon of C=C bonding and the sp3 carbon of C-C in the graphitic structure. The proportional content of these forms is 79.3% and 82.2% (C=C), and 6.4% and 1.9% (C-C) for the carbons C3 and C4, respectively. Moreover, the C1s spectrum includes three peaks attributed to the oxygen-containing functional groups. Peaks at 286.3 eV, 287.6 eV, and 288.5 are attributed to the carbon atoms in the C-OH/C-O-C, C=O, and O=C-O-R functional groups, respectively. Despite the visible difference in the O1s content for the analysed coal samples (Table 5), where for sample C3 the %At of O1s was 13.2% and for sample C4 it was 7.3%, the atomic analysis of the C1s carbon and the oxygen groups associated with it (Figure 12B,C) turned out to be very close. Due to the important role played by oxygen groups \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample Identifier** & **Name** & **Position** & **FWHM** & **\%At. Conc.** & **\% St.Dev.** \\ \hline \multirow{4}{*}{C1} & C1s & 284.5 & 1.8 & 84.8 & 0.105 \\  & O1s & 532.8 & 2.5 & 11.5 & 0.081 \\  & Si2p & 103.0 & 2.5 & 3.7 & 0.079 \\  & C1s & 284.5 & 1.8 & 88.4 & 0.087 \\  & O1s & 532.8 & 2.4 & 9.2 & 0.066 \\  & Si2p & 103.0 & 2.5 & 2.4 & 0.064 \\  & C1s & 284.5 & 1.7 & 82.4 & 0.156 \\ C3 & O1s & 532.8 & 2.6 & 13.2 & 0.114 \\  & Si2p & 103.0 & 2.3 & 4.4 & 0.129 \\  & C1s & 284.5 & 1.7 & 91.0 & 0.153 \\ C4 & O1s & 532.8 & 2.6 & 7.3 & 0.126 \\  & Si2p & 103.0 & 2.6 & 1.7 & 0.097 \\  & C1s & 285.0 & 2.9 & 76.9 & 0.119 \\ P1 & N1s & 399.0 & 2.4 & 3.6 & 0.090 \\  & O1s & 531.8 & 3.3 & 19.6 & 0.098 \\  & C1s & 285.0 & 2.5 & 92.3 & 0.149 \\ P2 & N1s & 399.8 & 2.5 & 2.6 & 0.140 \\  & O1s & 531.8 & 3.1 & 5.1 & 0.070 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: XPS results for all investigated samples. Positions of general peaks as a signal of photoelectrons from various energetic levels and atomic concentration with standard deviation. in the dye adsorption process, the energy states of the OIs atom were analysed (Figure 12D,E).