## 3 Results and Discussion
### Adsorption Performance
#### 3.2.5 Thermodynamic Analysis  
To evaluate the thermodynamic nature of m-cresol adsorption onto the XDA-1G resin, parameters including Gibbs free energy change (\(\Delta\)G\({}^{\circ}\)), enthalpy change (\(\Delta\)H\({}^{\circ}\)), and entropy change (\(\Delta\)S\({}^{\circ}\)) were determined using equilibrium data obtained at four different temperatures (303.15-333.15 K). The distribution coefficient (Kc) was calculated based on equilibrium adsorption capacity and concentration, and a van't Hoff plot (InKc vs. 1/T) was used to derive \(\Delta\)H\({}^{\circ}\) and \(\Delta\)S\({}^{\circ}\) from the slope and intercept, respectively. The thermodynamic fitting results, presented in Table 5 and visualized in Figure 11, demonstrate that \(\Delta\)G\({}^{\circ}\) values for 0.15 g resin were consistently negative across all temperatures, ranging from \(-1.542\) to \(-2.595\) kJ mol\({}^{-1}\). This confirms that the adsorption process is spontaneous under the investigated conditions. Notably, \(\Delta\)G\({}^{\circ}\) became more negative with increasing temperature, indicating that elevated temperatures enhance the spontaneity of m-cresol adsorption. The calculated \(\Delta\)H\({}^{\circ}\) was 9.090 kJ mol\({}^{-1}\), indicating that the adsorption process is endothermic. The positive enthalpy value suggests that energy input is required to facilitate the interaction between m-cresol molecules and the XDA-1G resin surface--likely through disruption of hydration shells and activation of specific binding sites. The positive entropy change (\(\Delta\)S\({}^{\circ}\) = 35.09 J mol\({}^{-1}\) K\({}^{-1}\)) further supports this observation, implying increased randomness at the solid-liquid interface. This can be attributed to desolvation of m-cresol and reorganization of water molecules during adsorption. Figure 11: Van’t Hoff plot for estimating thermodynamic parameters of m-cresol adsorption onto the XDA-1G resin. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**T** & **K\({}_{\text{c}}\)** & **\(\Delta\)Gv** & **\(\Delta\)H** & **\(\Delta\)S** \\
**(K)** & **K\({}_{\text{c}}\)** & **(kJ mol\({}^{-1}\))** & **(kJ mol\({}^{-1}\))** & **(J K\({}^{-1}\) mol\({}^{-1}\))** \\ \hline
303.15 & 1.839 & \(-1.542\) & & \\
313.15 & 2.035 & \(-1.893\) & & \\
323.15 & 2.441 & \(-2.244\) & 9.090 & 35.09 \\
333.15 & 2.479 & \(-2.595\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Thermodynamic fitting parameters for m-cresol removal by 0.15 g resin. These findings align well with the material's physicochemical characteristics. As confirmed by BET analysis and Figure 3b, the XDA-1G resin exhibits high specific surface area (1439 m\({}^{2}\) g\({}^{-1}\)) and hierarchical porosity, providing extensive adsorption sites and efficient mass transfer pathways. Moreover, FTIR and XPS analyses revealed surface oxygen functionalities (e.g., -OH, C=O) that facilitate specific interactions such as hydrogen bonding and \(\pi\)-\(\pi\) stacking, which are thermally activated. The thermodynamic data confirm that m-cresol adsorption onto the XDA-1G resin is a spontaneous and endothermic process accompanied by an increase in entropy. These characteristics, supported by structural and chemical analyses, affirm the XDA-1G resin's suitability for efficient removal of high-concentration phenolics under elevated temperature conditions. Post-adsorption FTIR and XPS characterization can provide valuable insights into hydrogen bonding interactions and surface chemical changes resulting from m-cresol adsorption. Although these analyses were not included in the current study, we acknowledge this limitation and propose their inclusion as a direction for future research. In addition to its high adsorption capacity and favorable performance under high-concentration conditions, the XDA-1G resin offers promising reusability. Although regeneration experiments were not the central focus of this study, it is worth noting that XDA-1G has already been successfully applied in industrial scenarios such as semi-coking wastewater treatment.