## 3 Results and Discussion
### Adsorption of 4-Ethylphenol and 4-Ethylguaiacol
#### 3.2.3 4-Ethylphenol and 4-Ethylguaiacol Removals from Like-Wine Solutions  
The adsorption isotherms of 4-EP and 4-EG were obtained on four untreated commercial ACs. In the dilute solutions, the ACs from Panreac and Merck adsorbed comparable quantities of 4-EP and 4-EG, as presented in Figure S2 (Supplementary Information). However, these amounts are quite superior to those achieved by the Norit granular ACs. From the concentrated solutions, (>0.2 mmol L\({}^{-1}\)) the maximum adsorption capacity of all of the ACs concerning 4-EG was always superior to 4-EP, as shown in Table 2. At high concentrations, 4-EG was adsorbed in greater extension, but the respective isotherm showed a more open knee. This allows us to state that 4-EP was adsorbed with greater affinity than 4-EG. The maximum adsorption capacity of the four ACs was also evaluated, vis-a-vis the two phenolic compounds, in the presence of 13% \(v/v\) of ethanol. From the data presented in Table 2, the presence of direct competition between ethanol and both phenolic compounds by the active centres is evident. These results are in line with the published results [19]. In the presence of 13% \(v/v\) of ethanol, the amount of 4-EP adsorbed was 63%, 67%, 70% and 84% of the amount adsorbed in the absence of ethanol, in the AC from Panreac, Merck, Norit 1240X and 1240W, respectively. In the AC from Panreac and Merck, the amount of 4-EG adsorbed was only 48% and 63%, respectively. However, with both granular ACs from Norit, the amount of 4-EG adsorbed was less than 20% of the amount of 4-EG adsorbed in the absence of ethanol. The difference between the maximum amount of each phenolic compound adsorbed highlights the greater affinity between the ACs and 4-EP. To increase the adsorptive capacities of ACs regarding 4-EG and 4-EP, Merck AC was submitted to different acid/basic treatments. The modified ACs were tested on the removal of 4-EP and 4-EG from an aqueous solution or a wine-like solution (containing 13% \(v/v\) of ethanol). The respective isotherms are presented in Figures 2 and 3. In the initial stage of the adsorption processes, there were a lot of active sites on the ACs surface and the strongly and weakly adsorbed components took the active sites easily, in agreement with published data [33]. However, for the same equilibrium concentration, the amount of 4-EG adsorbed by each AC was always higher than the 4-EP. However, the maximum amounts of 4-EP and 4-EG adsorbed were higher in the absence of ethanol, highlighting the competitiveness of ethanol by adsorption sites. The data presented in Table 3 allow us to conclude that the basic groups on the ACs surface favour the adsorption of 4-EP, but do not significantly impact the adsorption of 4-EG. Here, again, ethanol competes with 4-EP and 4-EG for the active centers. The results obtained from the ACs submitted to acidic treatments were not promising; however, this agrees with the results found in the literature [34]. Thus, it is possible to infer that ACs' surface chemistry is the foremost control factor in the 4-EG and 4-EP adsorption process, to the detriment of the textural properties. \begin{table}
\begin{tabular}{c c c c c} \hline \multicolumn{5}{c}{**Maximum Adsorption Capacity/mmol g\({}^{-1}\)**} \\ \hline \multirow{3}{*}{**Activated Carbon**} & \multicolumn{2}{c}{**4-Ethylphenol**} & \multicolumn{2}{c}{**4-Ethylguaiacol**} \\ \cline{2-5}  & **without Ethanol** & **with Ethanol** & **without Ethanol** & **with Ethanol** \\ \hline Merck & 1.59 & 1.06 & 2.02 & 0.96 \\ Panreac & 1.85 & 1.16 & 1.91 & 1.21 \\ Norit 1240X & 1.01 & 0.71 & 1.12 & 0.21 \\ Norit 1240W & 1.03 & 0.87 & 0.96 & 0.16 \\ \hline \end{tabular}
\end{table} 
Table 2: Adsorption capacity of the original ACs, concerning 4-EP and 4-EG, in the absence and presence of 13% (\(v/v\)) of ethanol, at pH = 3. Figure 3: Adsorption isotherms of 4-EG (open symbols) and 4-EP (closed symbols) obtained on modified ACs, in the presence of 13% (\(p/v\)) ethanol.