## 2 Results and Discussion
### Adsorption Experiment  
#### 2.9.1 Adsorption Kinetics  
Figure 9 and Figure S2 (SM) shows the kinetics of CFA adsorption onto the pure silica WMS and NR/WMS nanocomposites prepared without and with an aminopropyl group. From the plot of the CFA adsorption capacity (\(q_{\mathrm{t}}\)) over time, all materials exhibited a fast CFA adsorption in the first 30 min, and then reached equilibrium within 60 min. The calculated parameters obtained from the different kinetic models and the corresponding correlation coefficients (R\({}^{2}\)) for each adsorbent are summarized in Table 3. Regardless of the adsorbent type and aminopropyl group content, the adsorption of CFA was well represented by pseudo-second order kinetics, which indicated that the adsorption phenomena involved chemical processes [3; 38]. The WMS-NH\({}_{2}\) (0.25 mg g\({}^{-1}\)) had a higher adsorption capacity than the pristine WMS (0.08 mg g\({}^{-1}\)). This result was explained by the combined electrostatic and hydrogen-bonding interaction between the amino groups on the functionalized silica surface and the carboxyl groups of the CFA molecule.  
The beneficial effect of the rubber phase was seen when compared with the adsorption capacity of the NR/WMS with that of the WMS. The NR/WMS showed a 1.8-fold higher capacity in CFA adsorption than the WMS, although the nanocomposite had inferior textural properties to the pure silica one. This indicates that the hydrophobicity of the NR played an important role in the adsorption onto the NR/WMS material. Nevertheless, if one compares the adsorption kinetics between WMS-0.10 and NR/WMS with similar \(S_{\mathrm{BET}}\), it can be rationalized that the CFA adsorption preferentially occurred on the amino group. [PERSON] et al. demonstrated that the adsorption of gemfibrozil onto SBA-15 can be enhanced by grafting hydrophobic organo-functional groups onto the adsorbent surface [38]. Accordingly, we believe that the hydrophobic rubber phase promoted the diffus  
Figure 9: Kinetic curves of CFA adsorption onto (\(\Delta\)) WMS, (\(\lozenge\)) WMS-0.10, (\(\blacklozenge\)) NR/WMS, (\(\bullet\)) NR/WMS-0.05, (\(\blacktriangle\)) WMS-0.10 and (\(\blacksquare\)) NR/WMS-0.15.  
\begin{table}
\begin{tabular}{l c c c|c c c|c c c} \hline \hline \multirow{2}{*}{**adsorbent**} & \multirow{2}{*}{\(q_{\mathrm{r,exp}}\) (mg g\({}^{-1}\))} & \multicolumn{3}{c|}{**Pseudo-First Order**} & \multicolumn{3}{c|}{**Pseudo-Second Order**} & \multicolumn{3}{c}{**Richie-Second Order**} \\ \cline{2-10}  & & \(k_{1}\) & \(q_{\mathrm{r,real}}\) & \(R^{2}\) & \(k_{2}\) & \(q_{\mathrm{r,real}}\) & \(R^{2}\) & \(k_{2}\) & \(q_{\mathrm{r,real}}\) & \(R^{2}\) \\  & & (min\({}^{-1}\)) & (mg g\({  
and retarded the competitive adsorption of H\({}_{2}\)O in the solution onto the NR/WMS surface, while the silanol groups were the main active centers responsible for the CFA adsorption via a hydrogen-bonding interaction [39]. The combination of NR and aminopropyl group enhanced the kinetics of the CFA adsorption onto the NR/WMS-\(x\) series. At the same amount of APS loading, the adsorption capacity of the NR/WMS-0.10 was around 1.6-fold larger than that of the WMS-0.10. The NR/WMS-0.05 had the highest adsorption capacity of 0.93 mg g\({}^{-1}\), but the amount of CFA adsorbed was gradually decreased when the APS loading level was increased to 10 and 15 mol\(\%\). The lower adsorption capacity of the NR/WMS-0.10 and NR/WMS-0.15 was attributed to their poor textural properties (Table 2).