FIGURE 4 (a) CH4 and N2adsorption heat of MIL-120Al calculated using the Clausius–Clapeyron equation; (b) a comparison of the CH4 adsorption heat observed for some previously reported CH4-selective materials.
The isosteric heat of adsorption (Qst) for CH4 and N2 in the MIL-120Al were calculated based on the single-component adsorption isotherms obtained at 273 and 298 K using the Clausius–Clapeyron equation.54 Figure 4a shows the Qst at zero coverage for CH4 (20.87 kJ/mol) was higher than that of N2 (17.83 kJ/mol), suggesting the stronger interactions formed between the framework and CH4molecules. Interestingly, we found that upon increasing the CH4 loading, the Qst value were smooth lines with almost unchanged values (20.48–20.87 kJ/mol). This implies the energetic homogeneity of the MIL-120Al surface, and a similar phenomenon was also observed in [Co3(C4O4)2(OH)2].1In addition, when compared with the outstanding materials reported in the literature (see Figure 4b), MIL-120Al exhibits a low initial Qst value for CH4, which is beneficial to sorbent regeneration in an industrial process.