# Adsorption Separation of Various Polar Dyes in Water by Oil Sludge-Based Porous Carbon
## 3 Results
### The Adsorption Properties of OSC for Organic Dyes  
Figure 6a shows the effect of varying initial concentrations of adsorbates on the adsorption efficiency of OSC700. As shown, the adsorption capacity of OSC700 for the three organic dyes increases with increasing concentration. The adsorption capacity also varies depending on the type of dye, with MG exhibiting the highest capacity and CV  
Figure 5: XPS spectra of OS (**a–d**), OSC700 (**e–i**) and their fitting results. the lowest. This is because the polarity of the three organic dyes increases in the order of MG < MB < CV (Table 3). The weaker the polarity, the stronger the hydrophobic interaction and \(\pi\)-\(\pi\) EDA interactions between the organic dyes and the adsorbent, resulting in a higher removal rate. The adsorption mechanism of organic dyes by OSC is illustrated in Figure 7.  
The removal efficiency showed that MG maintained a high removal rate, with a slight decrease from 98.92% to 95.74% as the concentration increased from 10 ppm to  
Figure 6: Adsorption capacity and removal efficiency of three organic dyes at different initial concentrations (**a**), time (**b**), agent dosage (**c**), temperature (**d**) and pH (**e**), and Zeta of OSC700 (**f**). Figure 7: Adsorption mechanism of organic dyes by OSC. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \begin{tabular}{c} **Single-Point Energy** \\ **(RB3 LYP)/Hartree** \\ \end{tabular} & \begin{tabular}{c} **RMS Gradient** \\ **Norm/Hartree** \\ \end{tabular} & \
\begin{tabular}{c} **Dipole Moment/** \\ **Debye** \\ \end{tabular} &
\begin{tabular}{c} **Polarizability/a.u.** \\ **Polarizability/a.u.** \\ \end{tabular} \\ \hline MG & \(-843.6267\) & 0.000004 & 11.0223 & 306.5257 \\ MB & \(-899.0014\) & 0.000014 & 14.9658 & 335.8883 \\ CV & \(-1025.5797\) & 0.000067 & 26.6531 & 237.6323 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters for calculating the dipole moment of three organic dyes. 200 ppm. Meanwhile, the adsorption capacity increased significantly from 0.89 mg/g to 19.15 mg/g. In contrast, the removal rates of MB and CV, which have greater polarity, continuously decreased with increasing solution concentration, from 99.80% to 61.97% and 98.91% to 24.14%, respectively. The adsorption capacity increased gradually from 0.99 mg/g and 0.89 mg/g to 12.89 mg/g and 12.01 mg/g, respectively. The slope of the removal efficiency curve indicates that the adsorption of MG by OSC700 has not yet reached saturation, even when the solution concentration is increased to 200 ppm. In contrast, the removal efficiency of MB begins to decrease significantly when the solution concentration exceeds 60 ppm, suggesting that the active adsorption of MB by OSC700 has ended, and the subsequent process is driven by molecular diffusion and concentration gradient [51]. The removal efficiency of CV, the most polar dye, decreases linearly, while the adsorption capacity stabilizes gradually as the concentration exceeds 120 ppm. It is apparent that the adsorption of OSC700 on organic dyes is inversely proportional to the polarity of the dye, with this phenomenon becoming more pronounced at higher concentrations. Figure 6b shows the effect of different adsorption times on the adsorption efficiency of OSC700 for MG, MB, and CV. The adsorption efficiency of OSC700 for MG reaches 94.05% at 5 min and 97.47% at 120 min, respectively. The removal efficiencies of MB and CV also increase gradually, with optimal values of 98.91% and 79.62% achieved at 120 min. However, the removal rate and adsorption capacity decline after 120 min. According to the adsorption kinetics model, this phenomenon may be attributed to the desorption of organic dye molecules that are electrostatically bound to the C network on the OSC700 surface. During the adsorption process, the concentration of dye in the adsorption solution and OSC700 changes, with the concentration in OSC700 becoming significantly higher than in the solution.