# Aminated Covalent Organic Polymers for Anionic Dye Adsorption in Aqueous Systems
## 3 Results and Discussion
### Adsorption Mechanism  
In the dye adsorption experiments, ACOP exhibited effective anionic dye adsorption efficiency in the presence and absence of cationic dye molecules. The characteristic aromatic rings and the heterocyclic ring of the ACOP facilitated the adsorption of dye molecules, regardless of the surface charge of the ACOP and the dye molecules. To investigate the detailed adsorption mechanism of the prepared ACOP, FT-IR and XPS analyses were conducted (Figure 9, Table 4 and Figure S4). As depicted in Figure S4, the characteristic vibrations of ACOP were preserved, and new vibrations were observed at 2850, 1601, 1115, and 1028 cm\({}^{-1}\) for MO and 1031 and 783 cm\({}^{-1}\) for OG. These results imply that the dye molecules were successfully adsorbed on the ACOP surface and that the dye adsorption did not affect the structure of the prepared ACOP. Figure 8: Adsorption efficiency of ACOP in mixed-dye system (MB+MO and MB+CV) (initial dye concentration: 100 mg/L, mixed-dye system: 1:1 \(\
u/\
u\)%, initial adsorbent concentration: 2.0 g/L, and contact time: 1440 min). To obtain insights into the interactions between the prepared ACOP and the anionic dye molecules, their C 1 s and N 1 s XPS spectra were recorded and analyzed (Figure 9 and Table 4). The peaks attributed to \(\pi\)-\(\pi^{*}\) transition, C=N, C-N, C=C, and C-C in the C 1 s spectrum were observed in similar regions after dye adsorption. However, the areas of \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**ACOP** & \(\pi\)-\(\pi^{*}\)** & \multicolumn{3}{c}{**C 1 s**} & \multicolumn{3}{c}{**N 1 s**} & \multicolumn{3}{c}{**C-N=C**} \\  & **transition** & **C=N** & **C-N** & **C=C** & **C-C** & \(\pi\)**-excitation** & **C-N** & **N=N** \\ \hline Peak position & 293.4 & 287.8 & 286.3 & 285.3 & 284.8 & 405.2 & 400.4 & 399.1 \\ (eV) & 5.41 & 58.12 & 5.95 & 7.93. & 22.58 & 8.65 & 65.09 & 26.26 \\ \hline
**ACOP-MO** & \(\pi\)-\(\pi^{*}\)** & \multicolumn{3}{c}{**C 1 s**} & \multicolumn{3}{c}{**C-N**} & \multicolumn{3}{c}{**C-C**} & \multicolumn{3}{c}{**\(\pi\)-excitation**} & **C-N** & **C-N=C** \\  & **transition** & **C=N** & **C-N** & **C=C** & **C-C** & \(\pi\)**-excitation** & **C-N** & **C-N=N** \\ \hline Peak position & 292.5 & 287.8 & 286.3 & 285.3 & 284.8 & 405.2 & 400.4 & 399.1 \\ (eV) & 2.77 & 59.27 & 17.40 & 3.61 & 16.95 & 3.90 & 50.74 & 45.36 \\ \hline \multicolumn{1}{c}{**C 1 s**} & \multicolumn{3}{c}{**N 1 s**} & \multicolumn{3}{c}{**N 1 s**} \\ \cline{2-9}
**ACOP-OG** & \(\pi\)-\(\pi^{*}\)** & \multicolumn{3}{c}{**C=N**} & \multicolumn{3}{c}{**C-N**} & \multicolumn{3}{c}{**C-C**} & \multicolumn{3}{c}{**\(\pi\)-excitation**} & **C-N** & **C-N=C** \\  & **transition** & **C=N** & **C-N** & **C=C** & **C-C** & \(\pi\)**-excitation** & **C-N** & **C-N=N** \\ \hline Peak position & 293.4 & 287.8 & 286.2 & 285.4 & 284.8 & 405.0 & 399.4 & 398.4 \\ (eV) & Area & 2.01 & 67.90 & 9.43 & 2.54 & 18.12 & 3.41 & 52.59 & 44.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: C 1 s and N 1 s peak information obtained from XPS spectra of the prepared ACOP before and after dye adsorption. Figure 9: XPS spectra in the C 1 s and N 1 s regions of ACOP after MO and OG adsorption. these peaks changed by 2-11.5% after dye adsorption. Specifically, the areas of the peaks attributed to the carbon atoms in the benzene ring and \(\pi\)-\(\pi^{\star}\) transition in the triazine ring decreased after dye adsorption, while the areas of the peaks attributed to C=N and C-N increased. These findings could be ascribed to the fact that dye adsorption on the prepared ACOP proceeded through charge-charge interaction by nitrogen atoms, and \(\pi\)-\(\pi\) interaction could be affected by the benzene and triazine rings of ACOP (Figure 10). In the N 1 s spectrum, the areas of the peaks at around 399 eV, which were attributed to C-N=C and N=N, increased by 68-72%. By contrast, the areas of the peaks attributed to \(\pi\)-excitation and C-N decreased from 8.7% to 3.4-3.9% and from 65.1% to 50.7-52.6%, respectively.