# 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
Conversely, at high pH, the H\({}^{+}\) concentration decreases, resulting in good interaction between the dye ions and the surface sites. Furthermore, the interaction of surface functional groups at varying pH values can be more complex than mere electrostatic attraction. This involves surface complexation, where pH influences adsorption through complexation reactions, shifting their equilibrium and altering adsorption efficiency. Additionally, variations in pH can modify the biosorbent's structure, affecting its porosity, surface area, and the accessibility of adsorption sites, thereby influencing adsorption mechanisms beyond electrostatic attraction. Effect of Contact Time and Initial Dye Concentration  
To compare the performance of the raw adsorbents and highlight the effect of the wash water temperature on the adsorption capacity of the biosorbents, the results of the kinetic study of MB and CV adsorption on the raw materials are shown in Figure 11. The kinetic study revealed that the two varieties (MP and C) exhibited similar behavior, although the adsorption kinetics of _Maclura pomifera_ were faster than those of wild carob. The equilibrium time was reached after 60 min of contact for MB adsorption on MP, after 120 min for CV  
Figure 10: The effect of initial pH on the adsorption capacity of CV on Maclura pomifera and wild carob. \(C_{0}\) = 100 mg L\({}^{-1}\), T = 23 \(\pm\) 2 \({}^{\circ}\)C, V = 250 rpm, r = 1 g L\({}^{-1}\). Figure 9: The effect of initial pH on the adsorption capacity of MB on Maclura pomifera and wild carob. \(C_{0}\) = 100 mg L\({}^{-1}\), T = 23 \(\pm\) 2 \({}^{\circ}\)C, V = 250 rpm, r = 1 g L\({}^{-1}\). adsorption on MP, and after 240 min for both MB and CV adsorption on C. These differences can be attributed to the structural and chemical properties of the adsorbents. For example, Maclura pomifera (MPC) has a larger specific surface area (237.3 m\({}^{2}\) g\({}^{-1}\)) than wild carob (CC) at 79.4 m\({}^{2}\) g\({}^{-1}\). A larger specific surface area, along with more developed porosity, means that there are more active sites available, which increase the rate of adsorption. Additionally, MPC contains more acidic surface functional groups (6.45 mmol g\({}^{-1}\)) than CC (3.02 mmol g\({}^{-1}\)), further contributing to the faster adsorption of cationic dyes. The quantities adsorbed by MPC were slightly higher than those by CC, specifically 80.1 mg/g and 72.1 mg/g for MB and 84.9 mg/g and 81.2 mg/g for CV. The adsorption capacities of MP and C were negatively affected by the increase in wash water temperature. These results are consistent with the predictions based on the physical and chemical properties of the materials. Figures 12 and 13 show a study of the adsorption kinetics of the raw materials washed with cold water as a function of the initial concentrations of MB and CV. Theses adsorption kinetics show a commonly observed behavior for the adsorption of cationic dyes. All the curves show a rapid increase in the quantity adsorbed during the initial phase of the contact time, which then slows down, with each curve approaching an asymptote parallel to the time axis. The slope at the origin is almost infinite, indicating a very high affinity between the adsorbent and the adsorbate [71]. This behavior can be explained by the abundance of available sites on the adsorbent surface at the beginning of adsorption. Most of these sites are quickly occupied, and the remaining sites become increasingly difficult to access due to the repulsive forces between the molecules adsorbed on the biosorbent surface and those in the solution. Similar observations have been reported by other researchers [70; 74]. The figures also show that the adsorbed amount increased with the initial concentration of MB and CV. This common result is generally explained by the fact that a higher initial concentration increases the driving force due to the concentration gradient, thereby enhancing retention.