# Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption
## 3 Results and Discussion
### Adsorption of Pesticides onto Bentonite and Modified Bentonite
#### 3.2.2 Simultaneous Adsorption of Various Pesticides in Solutions  
The results of each pesticide adsorption (single-component) and simultaneous adsorptions of the four pesticides (quaternary-component) from aqueous solution onto all adsorbents at ambient temperature and at initial pH of solution (6.5 \(\pm\) 0.5) without pH adjustment are shown in Figures 7 and 8, respectively. All adsorbents can remove PQ\({}^{2+}\) from both single and quaternary-component systems. In the quaternary-component system, the adsorption of PQ\({}^{2+}\) was slightly reduced compared with single-component due to the PQ\({}^{2+}\) adsorption occurring mainly inside the interlayer space of the adsorbents. Accordingly, the other pesticides (atrazine diuron and 2,4-D) in the quaternary-component do not affect the adsorption of PQ\({}^{2+}\) in the interlayer space of the adsorbents. The 2,4-D adsorption is decreased, except for BA\({}_{0.5}\)C\({}_{500}\) with the same adsorption capacity as in a single component, possibly due to the positive zeta potential of BA\({}_{0.5}\)C\({}_{500}\) surface (see Table 4) which provides an electrostatic attraction from the positively charged surface and 2,4-D (anion pesticide). Atrazine still prefers BC\({}_{500}\)A\({}_{0.5}\) in quaternary-component, but the adsorption capacity is lower than that in a single-component due to the limited number of active sites (as mentioned in Topic 2.6). In contrast to diuron (non-polar pesticide), it was found that the adsorption of diuron in the quaternary-component was higher than that in the single-component. This could be explained by the simultaneous adsorption; PQ\({}^{2+}\) adsorbed at the surface of the adsorbents can act as an additional active site, which  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{3}{c}{**[PERSON]**} & \multicolumn{3}{c}{**[PERSON]**} & \\ \cline{2-7}  & **qm** & **K\({}_{\mathbf{L}}\)** & \multirow{2}{*}{**R2**} & \multicolumn{2}{c}{**K\({}_{\mathbf{F}}\)**} & \multirow{2}{*}{**n**} & \multirow{2}{*}{**R2**} \\ \cline{2-7}  & **(mg g\({}^{-1}\))** & **(L mg\({}^{-1}\))** & & & **(mg g\({}^{-1}\)). (L mg\({}^{-1}\))\({}^{1/n}\)** & \\ \hline B & 4.76 & 18.77 & 0.9972 & 6.69 & 1.81 & 0.8977 \\ BA\({}_{0.5}\) & 1.75 & 100.39 & 0.9966 & 3.54 & 1.56 & 0.9266 \\ BC\({}_{500}\) & 3.58 & 23.26 & 0.9983 & 5.12 & 1.71 & 0.9101 \\ BA\({}_{0.5}\)C\({}_{500}\) & 0.85 & 52.63 & 0.9987 & 11.83 & 5.26 & 0.9726 \\ BC\({}_{500}\)A\({}_{0.5}\) & 2.11 & 43.90 & 0.9986 & 2.44 & 1.43 & 0.8715 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Langmuir and Freundlich paraquat adsorption isotherm constants.  
is competent to attach diuron through the interaction between dipole (C = O of diuron) and cation (PQ2+). Therefore, the presence of PQ2+ in quaternary-component enhances diuron adsorption. The maximum total values of the simultaneous adsorption of various pesticides from aqueous solution belong to BC500A0.5, indicating that BC500A0.5 is the most suitable for the simultaneous removal of different types of pesticides. Hence, it could be regarded as an effectively multifunctional adsorbent.  
Figure 8: Adsorption of quaternary-component pesticides (with each pesticide 50 mg L\({}^{-1}\)) at pH 6.5 \(\pm\) 0.5 onto bentonite and modified bentonite.  
Figure 7: Adsorption of single-component pesticide with a concentration of 50 mg L\({}^{-1}\) at pH 6.5 \(\pm\) 0.5 onto bentonite and modified bentonite.