## 3 Results and Discussion
### Resticide Adsorption Studies
#### 3.3.2 Isotherm Adsorption Studies  
The adsorption isotherms of the three studied pesticides onto the synthesized adsorbents are shown in Figure 4a-d. The initial concentration of micropollutant was fixed at 50 mg/L, whereas the dose of adsorbent was varied within the range of 0.05-1.5 mg/mL. From the results, the best adsorption capacities for the three contaminants were found for AC-ZnCl\({}_{2}\): q\({}_{e}\) = 128.9, 126.8, and 166.1 for ACT, THM, and IMD, respectively. As can be observed, all the adsorption isotherms showed a multilayer profile. Thus, they could be classified as type S-3 and S-4, according to the classification established by [PERSON] et al. [40]. The S-type isotherms are characterized by a steep slope, and as the adsorbate concentration increases, the adsorption capacity approaches a first plateau. The first plateau is attributed to saturation caused by the termination of the first monolayer. Then, as the adsorbate concentration increases, a vertical rearrangement of the adsorbed molecules occurs, and more active sites become available for adsorption [41]. Therefore, the newly available adsorption sites lead to a further increase of the adsorption capacity, and a second plateau occurs, which is attributed to a second layer. These S-type isotherms may also be the result of a competitive effect between the solvent and the adsorbate towards the active sites available for adsorption [42]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Pseudo-First-Order Model**} & \multicolumn{3}{c}{**Pseudo-Second-Order Model**} \\ \hline
**adsorbent** & **Pesticide** & \begin{tabular}{c} **qexp** \\ **(mg/g)** \\ \end{tabular} & \begin{tabular}{c} **qtver** \\ **(mg/g)** \\ \end{tabular} & \begin{tabular}{c} **k1** \\ **(h\({}^{-1}\))** \\ \end{tabular} & **R\({}^{2}\)** & \
\begin{tabular}{c} **qtver** \\ **(mg/g)** \\ \end{tabular} &
\begin{tabular}{c} **k2** \\ **(g/mg-h)** \\ \end{tabular} & **R\({}^{2}\)** \\ \hline
**AC-ZnCl2** & **ACT** & 84.3 & 84.2 & 0.28 & 0.870 & 78.8 & 0.71 & 0.867 \\
**AC-ZnCl2** & **THM** & 96.9 & 96.9 & 1.39 & 0.804 & 96.7 & 3.50 & 0.840 \\
**IMD** & 105.7 & 105.7 & 1.37 & 0.824 & 105.0 & 2.95 & 0.861 \\ \hline
**AC-FeCl3** & **ACT** & 70.1 & 70.0 & 0.17 & 0.929 & 65.0 & 0.39 & 0.931 \\
**THM** & 66.1 & 66.1 & 0.16 & 0.968 & 93.8 & 1.08 & 0.863 \\
**IMD** & 75.9 & 64.3 & 0.02 & 0.943 & 59.0 & 70.2 & 0.963 \\ \hline
**AC-Fe(NO3)3** & **ACT** & 66.4 & 60.4 & 0.02 & 0.967 & 55.6 & 0.80 & 0.941 \\
**THM** & 135.0 & 124.5 & 0.02 & 0.984 & 111.9 & 0.02 & 0.964 \\
**IMD** & 35.4 & 35.4 & 0.13 & 0.887 & 33.0 & 0.55 & 0.899 \\ \hline
**AC-Fe2(SO4)3** & **ACT** & 23.3 & 23.3 & 0.28 & 0.853 & 39.8 & 29.47 & 0.933 \\
**THM** & 194.8 & 156.1 & 0.01 & 0.912 & 138.7 & 0.01 & 0.904 \\
**IMD** & 21.5 & 21.5 & 0.26 & 0.888 & 64.4 & 2.55 & 0.946 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Kinetic model parameters for the adsorption of ACT, THM, and IMD onto the carbon materials. Figure 4: Adsorption isotherms of the three pesticides onto the (**a**) AC-ZnCl2, (**b**) AC-FeCl3, (**c**) AC-Fe(NO3)3, and (**d**) AC-Fe2(SO4)3 activated carbons. Correlation of the experimental equilibrium data to empirical models is essential for the practical interpretation of scientific results. In this work, the Langmuir, Freundlich, Sips, and Guggenheim-Anderson-de Boer (GAB) isotherm models were used to fit the experimental adsorption data. The Langmuir isotherm model supposes that the adsorption process takes place in a monolayer, that the solid surface is energetically homogeneous, and that the molecules are adsorbed on well-defined sites, i.e., without migration of the adsorbate from one active site to another [43].