# Adsorption of Metolachlor and Its Transformation Products, ESA and OXA, on Activated Carbons
## 3 Results
### Characterization of Precursors and Activated Carbons
#### 3.1.2. Physico-Chemical Characterization of Activated Carbons  
The activation protocols applied for both lignocellulosic materials yielded highly porous activated carbons with specific surface areas ranging between 1500 and 2200 m\({}^{2}\)/g (Table 2, [19]). The N\({}_{2}\) adsorption/desorption isotherms at \(-\)196 \({}^{\circ}\)C of the four activated carbons are presented in Figure 1. All of them correspond to a Type I isotherm according to the IUPAC classification [27], which is characteristic of mainly microporous materials. Comparing the materials as a function of used precursor (R-KC and S-KC samples obtained from rape and sunflower, respectively), higher activation yield was obtained for the S-KC material (Table 2); this fact is linked with the higher lignin content on the sunflower residues (Table 1) [28]. With respect to the porosity, similar isotherm shape was obtained for both materials, with a steep knee at low relative pressures and a flat plateau at the higher range; however, the sample prepared from rape residue revealed the presence of a smooth hysteresis loop expanded from 0.8 to 1 of p/p\({}_{0}\). Although similar surface areas were obtained for both materials, the rape residue allowed the preparation of activated carbon with higher total pore volume and greater development of mesoporous (Table 2), probably associated with the higher presence of inorganic species, such as potassium and calcium (Table 1), which can act as intrinsic activating agents during the thermal process. It is important to note that due to the different nature of both precursors (powder and flakes for rape and sunflower, respectively), the K\({}_{2}\)CO\({}_{3}\)/raw residue impregnation was physical (for rape) and wet (for sunflower) to facilitate the operation. The sample R-KC was activated following both impregnation processes rendering similar porous features (Figure S1 and Table S2, ESI), assuring that the experimental impregnation protocol did not affect the final porosity of the activated materials. \begin{table}
\begin{tabular}{l c c} \hline  & **Rape Straw** & **Sunflower Seed Shell** \\ \hline Ashes (\%) & 8.2 \(\pm\) 0.1 & 2.9 \(\pm\) 0.3 \\ Cellulose (\%) & 52.1 \(\pm\) 0.4 & 43.0 \(\pm\) 3 \\ Hemicellulose (\%) & 15.2 \(\pm\) 1.1 & 29.2 \(\pm\) 3.8 \\ Lignin (\%) & 4.6 \(\pm\) 0.6 & 20.1 \(\pm\) 0.8 \\ Total C (\%) & 45.2 & 50.2 \\ P (ppm) & 2366.0 & 236.9 \\ K (ppm) & 15,370.0 & 7110.0 \\ S (ppm) & 5813.0 & 1008.0 \\ Ca (ppm) & 22,690.0 & 3312.0 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of both lignocellulosic precursors. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \multirow{2}{*}{**Sample**} & **SagT** & **V\({}_{\text{total}}\)** & **W\({}_{\text{0}}\)** & **V\({}_{\text{meco}}\)** & **L** & **Yield \({}^{*}\)** & **Elemental analysis (wt. \%)** & **Superficial** & **Acidity** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **b** & **(cm\({}^{2}\)/g)** & **c** & **(mm) \({}^{4}\)** & **(\%)** & **C** & **N** & **S** & **O** & **pH** & **(mmol H\({}^{4}\)/g)** \\ \hline S-KC & 2024 & 0.86 & 0.76 & 0.04 & 1.0 & 22 & 88.3 & \(<\)0.02 & \(<\)0.1 & 5.6 & 6.0 & 1.07 \\ R-KC & 2220 & 1.05 & 0.83 & 0.13 & 1.2 & 15 & 86.4 & \(<\)0.02 & 0.5 & 6.6 & 6.6 & 1.85 \\ R-PO & 1466 & 0.72 & 0.49 & 0.14 & 1.4 & 41 & 67.6 & 0.8 & \(<\)0.1 & 24.4 & 3.5 & 2.19 \\ AQ630 & 1016 & 0.60 & 0.38 & 0.20 & 1.2 & – & 84.7 & 0.1 & n.a & 2.3 & 7.4 & 0.94 \\ \hline \end{tabular}  
* Evaluated at p/p\({}_{0}\)-0.99;
* evaluated by DR method;
* evaluated by the 2D-NLDFT-HS method;
* pore size evaluated by Stoeckli–Ballerini equation;
* after washing; n.a.: No analysed.  
\end{table} 
Table 2: Textural parameters obtained from the N\({}_{2}\) adsorption/desorption isotherms at \(-\)196 \({}^{\circ}\)C, synthesis yield and chemical composition of studied activated carbons. The activation process with K\({}_{2}\)CO\({}_{3}\) as the activating agent was studied by thermogravimetry.