# Carbon from Bagasse Activated with Water Vapor and Its Adsorption Performance for Methylene Blue
## 3 Results and Discussion

Table 2: Surface area (m\({}^{2}\)/g), total pore volume (cc/g), and the average pore size (nm) of the prepared samples. Figure 6: SEM images of the carbonized-carbon and the activated-carbon at 500 \({}^{\circ}\)C (AC500), 600 \({}^{\circ}\)C (AC600), 700 \({}^{\circ}\)C (AC700). The MB adsorption on AC700 for various initial concentrations reaches equilibrium after 30 min (Figure 8). Table 3 lists the equilibrium concentration, Ce, and the mass adsorbed at equilibrium, \(q_{e}\), for each initial concentration, along with the isotherm parameters. The theoretical maximum adsorption capacity of the AC700 adsorbent is 303 mg/g adsorbent, based the surface area of AC700 and the covered area of MB molecules [31]. However, the Langmuir isotherm found a maximum loading of MB molecules on the AC700, \(a\), of 21.008 mg/g. Figure 8: The adsorption curves at various time and three conditions of initial MB concentration. Figure 7: The pore distribution curve of the activated-carbon compared with the carbonized bagasse. The large difference between theoretical loading and Langmuir loading, as shown in Table 3, i.e., 21.008 mg/g, confirmed weak interactions between the adsorbate-adsorbent surface. Methylene blue is a macromolecule with a chemical structure as described in Figure 9 [51], and the proposed adsorption mechanism is explained through the interaction between carbon and methylene blue molecules [52]. D-R model application found adsorption energy, \(E\), of 3.536 kJ/mol, confirming physical adsorption because the energy was less than 8 kJ/mol [33]. The interaction of MB molecules with the AC surface is described in Figure 9 considering the high electron density within the \(\pi\) orbital, the electrostatic potential force of N+, and the potential hydrogen bond formation. Those possible interactions were also predicted by other previous publications [52; 53; 54]. The presence of Cl+ as counter ion would minimize the interaction between the MB-MB molecules, with the only remaining possibility being hydrogen bonding, because the \(\pi\)-\(\pi\) coupling interaction would also be difficult to form due to the steric effect caused by the surface functional groups of C=N chromophores. \begin{table}
\begin{tabular}{c c c} \hline
**Isotherm** & **Parameters** & **Value** \\ \hline [PERSON] & \(a\) (mg/g) & 21.008 \(\pm\) 0.021 \\  & \(b\) (L/mg) & 0.685 \(\pm\) 0.001 \\  & R2 & 0.999 \\ \hline [PERSON] & \(K_{F}\) & 1.076 \(\pm\) 0.327 \\  & \(1/n\) & 0.881 \(\pm\) 0.268 \\  & \(R^{2}\) & 0.696 \\ \hline D–R & \(B\) (J/mol)\({}^{-2}\) & \((-4\pm 0.220)\times 10^{-8}\) \\  & E (kJ/mol) & \(3.536\pm 0.194\) \\  & \(R^{2}\) & 0.945 \\ \hline \end{tabular}
\end{table} 
Table 3: The isotherm parameters. Figure 9: Scheme of the proposed-interaction between carbonaceous surface and methylene blue. The interaction between the organic compound with carbon can be \(\pi\rightarrow\pi\) electron-donor acceptor, hydrophobic interaction, hydrogen bonding, electrostatic and covalent interaction, and Van der Waals forces, which may work individually or simultaneously [55]. The hydrophobic side of carbon provides a high \(\pi\) electron of sp\({}^{2}\) carbons, in which MB molecules interact through \(\pi\)-\(\pi\) electron coupling. Moreover, the acidity of the AC surface increases the possibility of electrostatic interactions and the formation of hydrogen bonding between the AC surface and the MB molecules. The AC700 has an acidity value of 40.3060 \(\pm\) 8.2850 mg NH\({}_{3}\)/g AC, which is higher than the activated-carbon prepared from fiber (ACF) produced by oxy fluorination, i.e., 31.29 mg NH\({}_{3}\)/g ACF [56]. The contribution of the surface functional group is supported by the FTIR spectrum before and after MB adsorption (Figure 10). The FTIR spectra of AC700 after MB adsorption shows a new peak at the wavenumber of 1376 cm\({}^{-1}\), which is related to the N=O functional group.