# Effect of Washing Temperature on Adsorption of Cationic Dyes by Raw Lignocellulosic Biomass
## 3 Results and Discussion
### Results of Methylene Blue and Crystal Violet Adsorption on Raw Materials  
#### 3.2.1 The Effect of Various Physico-Chemical Parameters  
The Effect of pH  
pH is an important factor in adsorption studies, as it can affect the structures of both the adsorbent and the adsorbate, as well as the adsorption mechanism. Therefore, it is crucial to know the adsorption efficiency at different pH values. The variation in the adsorption capacity of methylene blue (MB) and crystal violet (CV) by _Maclura pomifera_ and wild carob is shown in Figures 9 and 10, respectively. The data presented in these figures indicate that the evolution of MB and CV adsorption with pH for the two varieties (MP and C) is very similar. The change in the surface charge was the main factor controlling the adsorption of MB and CV. It is noted that, for all six materials, there was a clear improvement in the adsorption capacity of the dyes with increasing pH, which then became substantially constant. Similar behavior has been observed in numerous studies [70; 71; 72]. This can be explained by the fact that when the pH is higher than the pHpzc, the surface of the biosorbents is negatively charged, and the molecules of cationic dyes (MB and CV)  
Figure 8: FTIR spectra of CC, CW, and CH. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multicolumn{6}{c}{**Wave Number (cm \({}^{-1}\))**} & \multicolumn{6}{c}{**FTIR Interpretation**} \\ \hline \multicolumn{6}{c}{**In This Study**} & \multicolumn{6}{c}{**In the**} \\ \hline
**MPC** & **MPW** & **MPH** & **CC** & **CW** & **CH** & **Bibliography** & **Type of Vibration** & **References** \\ \hline
3450 & 3450 & 3450 & 3428 & 3428 & 3428 & 3600–3300 & \multicolumn{6}{c}{Elongation vibrations of O-H hydroxyI groups (carboxylic acids, alcohols, phenols, cellulose, pectin, absorbed water, and lignin)} & [58; 59; 60] \\ \hline
2924 & 2924 & 2924 & 2924 & 2924 & 2924 & 2920 & \multicolumn{6}{c}{Asymmetrical and symmetrical C-haliphatic elongation vibration} & [61] \\
2855 & 2855 & 2855 & 2855 & 2855 & 2855 & 2850 & \multicolumn{6}{c}{elongation vibration} & [62; 63] \\ \hline
2370 & 2370 & 2370 & 2370 & 2370 & 2370 & 2370 & 2350 & \multicolumn{6}{c}{Elongation vibrations of the C=C bond of the alkyme group} & [62; 63] \\
2399 & 2345 & 2345 & 2345 & 2345 & 2345 & 2339 & \multicolumn{6}{c}{Longoation vibrations (ketones, aldehydes, lactones, or carboxyl groups)} & [64] \\ \hline
1649 & 1649 & 1649 & - & - & - & 1637 & \multicolumn{6}{c}{C=O elongation vibrations in cyclic amides} & [65] \\ \hline - & - & - & 1628 & 1628 & 1628 & 1637–1606 & \multicolumn{6}{c}{Symmetric and asymmetric C-O elongation vibration in ionic carboxylic groups (COO-)} & [51] \\ \hline
1520 & 1520 & 1520 & 1520 & 1520 & 1520 & 1520 & 1600–1500 & \multicolumn{6}{c}{Elongation vibrations of C-xC bonds in condensed aromatic rings} & [66] \\ \hline
1449 & 1449 & 1449 & 1458 & 1458 & 1458 & 1458 & \multicolumn{6}{c}{Elongation vibrations of C=O in ether} & [67] \\ \hline - & - & - & 1384 & 1384 & 1384 & 1384 & \multicolumn{6}{c}{Deformation vibrations of C\({}_{\text{H}}\) bond} & [68] \\ \hline
1259, & 1259 & 1259 & 1259, & 1259, & 1113, & 1042 & 1350–900 & \multicolumn{6}{c}{C-O bond elongation vibrations in alcohols, phenols, acids, ethers, or esters} & [59; 60] \\
1116, 1076 & 1259 & 1259 & 1113, & 1042 & 1113, & 1042 & \multicolumn{6}{c}{Deleon, acids, ethers, or esters} & [59; 60] \\ \hline
832,674 & 702 & 702 & - & 669 & 669 & 858–615 & \multicolumn{6}{c}{Deformation vibrations of C harmonics} & [69] \\ \hline
538 & - & - & 569,515 & - & - & 500–600 & \multicolumn{6}{c}{Vibration of aromatic rings} & [69] \\ \hline \end{tabular}
\end{table} 
Table 5: Surface functions of raw materials identified by infrared spectroscopy. are positively charged [73]. Adsorption can be envisaged by the electrostatic interactions between the different charges of the adsorbents and dyes. At low pH, the sorbent surface is surrounded by H\({}^{+}\) ions, which reduce the interaction of the dye cations with the adsorbent sites.