## 3 Results and Discussion
### Adsorption Isotherm  
An adsorption isotherm can be used to clarify the interaction mechanism between adsorbent and adsorbate. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models were applied to study the saturated adsorption behavior and capacity (Supplementary Materials). Adsorption isotherms of anilines and initial aniline concentrations in the ranges of 100-1000 mg/L at 20, 25, and 30 \({}^{\circ}\)C are displayed in Figure 9. The isotherm parameters and correlation coefficient (\(R^{2}\)) are listed in Table 2.  
The adsorption equilibrium was significantly affected by the initial concentrations of anilines at the different temperatures. \(q_{e}\) quickly increased with the increase of initial concentrations until reaching equilibrium. In addition, \(q_{e}\) onto the CDM-HCP obviously decreased with rising temperature, implying that this is of an exothermic nature [39]. The \(q_{\rm max}\) (mg) values of aniline, \(p\)-MA, \(p\)-CA, and \(P\)-ABC calculated from the Langmuir model were 163.25, 225.44, 291.50, and 752.81 mg/g at 20 \({}^{\circ}\)C, respectively (Table 2). From \(R^{2}\), the Langmuir isotherm model demonstrated a better application to the adsorption of \(p\)-MA and \(p\)-ABC onto the CDM-HCP, indicating their anchoring to the functional groups of the CDM-HCP with the formation of monolayer surface coverage. In contrast, aniline and \(p\)-CA obeyed the Freundlich isotherm model better, indicating that this model was used to characterize the equilibrium adsorption with multilayer adsorption. Previous results indicated that if \(1<n<10\), the adsorption can occur smoothly, it is difficult to take place if \(0.5<n<1\), and it cannot perform for \(n<0.5\) for the Freundlich equation [40]. From Table 2, \(n\) values calculated from the Freundlich equation are all in the range of 1.26 to 3.57, implying that the CDM-HCP would be suitable for enriching the adsorption of anilines. The \(E_{\rm a}\) value of the D-R isothermal adsorption model is the main index to judge whether the adsorption is physisorption or chemisorption. From Table 2, the \(E_{\rm a}\) values are all greater than 16 kJ/mol, showing that the adsorption process is chemisorption [41]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**Parameter**} & \multicolumn{5}{c}{**Adsorbate**} \\ \cline{3-6}  & & **Aniline** & \(p\)**-MA** & \(p\)**-CA** & \(p\)**-ABC** \\ \hline \multirow{3}{*}{this study} & \(C_{0}\) (mg/L) & 1000 & 1000 & 1000 & 1000 \\  & \(q_{\rm e,expt}\) (mg/g) & 148.97 & 198.45 & 293.71 & 622.91 \\  & \(k_{1}\) (min\({}^{-1}\)) & \(4.80\times 10^{-3}\) & \(5.00\times 10^{-3}\) & \(4.90\times 10^{-3}\) & \(2.52\times 10^{-3}\) \\ pseudo-first-order & \(q_{\rm e,cal}\) (mg/g) & 142.61 & 192.59 & 291.58 & 657.69 \\  & \(R^{2}\) & 0.97 & 0.98 & 0.97 & 0.92 \\  & \(k_{2}\) (g/mg/min) & \(1.54\times 10^{-4}\) & \(6.75\times 10^{-5}\) & \(3.73\times 10^{-5}\) & \(2.24\times 10^{-5}\) \\ pseudo-second-order & \(q_{\rm e,cal}\) (mg/g) & 130.89 & 204.50 & 309.60 & 684.93 \\  & \(R^{2}\) & 0.99 & 0.99 & 0.99 & 0.99 \\  & \(k_{\rm int}\) (g/(mg\(\cdot\)min\({}^{1/2}\))) & 2.18 & 4.00 & 7.02 & 13.92 \\  & \(k_{\rm d}\) & 67.85 & 85.04 & 99.44 & 279.07 \\  & \(R^{2}\) & 0.92 & 0.94 & 0.96 & 0.97 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Kinetic parameters for the adsorption of aniline compounds on the CDM-HCP at 20 \({}^{\circ}\)C.