# Effect of Washing Temperature on Adsorption of Cationic Dyes by Raw Lignocellulosic Biomass
## 3 Results and Discussion
### Characterization of Materials
#### 3.1.2 Chemical Characterization  
Elemental Analysis of the Materials  
Table 2 presents the elemental composition of _Maclura pomifera_ and wild carob washed with cold and hot water. These results show that the elemental composition of the adsorbents is typical of lignocellulosic material and is consistent with the findings often cited by other authors [50; 51; 52]. However, it should be noted that MPH and CH contain a higher proportion of carbon and a lower content of heteroatoms. This can be explained by the  
Figure 4: SEM image of CC. Figure 5: SEM image of CH. Figure 3: SEM image of the MPH. elimination of soluble impurities at high temperatures. Various consequences may result from this change in the elemental composition of biosorbents, particularly in relation to their behavior in aqueous solution, such as the drop in the acidity of MPH and CH resulting from the reduction in oxygen content [53]. pH at Zero Charge Point  
The obtained pH\({}_{\text{pzc}}\) values (Table 3) allowed for determining the acidic or basic nature of an adsorbent and, depending on the pH of the solution, its net surface charge [54; 55; 56]. Figure 6 shows a family of curves, indicating that all the supports had an acidic surface that decreased as the temperature of the wash water increased. These results are consistent with the previous findings from the elemental analysis. Analysis of Surface Functions by the Boehm Method  
The Boehm titration results (Table 4) revealed that all the materials had fewer basic groups compared to acidic groups, confirming their acidic nature. The surface chemistry of both materials was influenced by the temperature of the wash water. Specifically, there was decreases in both total acidity and total basicity, resulting in a reduction in the surface functional groups. The data indicate that the wild caroby variety was acidic, though to a lesser extent than _Maclura pomifera_, with more acidic sites, suggesting a higher presence of oxygenated groups. These groups enhance the adsorption of cationic dyes. The findings are consistent with those reported in the literature [57]. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{8}{c}{**Elemental Analysis (\% by Mass)**} \\ \cline{2-11}  & **C** & **O** & **Ca** & **S** & **Si** & **K** & **Al** & **N** & **Mg** & **P** \\ \hline MPC & 45.4 & 40.2 & 1.5 & 1.0 & - & 0.9 & 4.1 & 5.2 & 0.7 & 1.0 \\ \hline MPH & 62.4 & 36.1 & 0.6 & 0.4 & - & - & 0.5 & - & - & - \\ \hline CC & 40.4 & 48.1 & 8.9 & 0.5 & 0.4 & 0.8 & 0.9 & - & - & - \\ \hline CH & 52.6 & 47.2 & - & 0.2 & - & - & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Elemental composition of raw biosorbents. Figure 6: Isoelectric points of raw adsorbents (m = 25 mg, V = 25 mL, stirring speed = 250 rpm, and t = 24 h). Analysis of Surface Functions by Fourier Transform Infrared Spectroscopy (FTIR)  
To achieve a more comprehensive identification of the surface functions of the raw biosorbents and to highlight the impact of the wash water temperature on their surface chemistry, infrared spectroscopy was employed. The spectra for the materials washed with cold, warm, and hot water are presented in Figures 7 and 8. Table 5 summarizes the characteristic functional groups on the surfaces of the raw materials, including their nature and wavelength. From Figures 7 and 8, the following can be observed:  
* The infrared spectra exhibit a similar peak distribution for both _Machura pomifera_ (MP) and wild carob (C) varieties. * The spectra indicate that the active surface functional groups for both types of biosorbents are primarily -OH bonds from polymers and polysaccharides, as well as -CH\({}_{2}\) and -COOH bonds, which are known to play a significant role in dye adsorption. * The spectra for each variety are nearly identical, with the primary difference being the relative intensity of the peaks.