FIGURE 2 (a) CO2 adsorption and desorption
isotherms obtained for MIL-120Al at 195 K; (b) pore size distribution of
MIL-120Al; (c) TG curve obtained for MIL-120Al; (d) comparison of the pH
value of the initial solution and thermal stability of conventional
CH4/N2 separation materials.
Limited by the small window diameter, the pore-size of MIL-120Al cannot
be obtained using N2 as a probe (Figure S2). Thus, a
carbon dioxide sorption experiment was performed at 195 K, as shown in
Figure 2a. The isotherm obtained for MIL-120Al shows a typical type I
behavior, indicating its microporous nature. The
Brunauer–Emmett–Teller (BET) surface area and pore volume were 529
m2/g and 0.24 cm3/g, respectively.
These values were slightly higher than those previously reported, which
may be attributed to the sample washing step using high temperature
methanol.44 The pore size distribution was evaluated
using the Horvath–Kawazoe model (Figure 2b) and the calculated pore
size (4.8 Å) was consistent with the results obtained from the crystal
structure (5.4 × 4.7 Å).40 From a practical point of
view, the pH value of the initial solution and thermal stability are two
key metrics for evaluating the adsorbent. Figure 2c and Table S1 show
MIL-120Al can only be synthesized in an alkaline environment (pH
>7) among the conventional
CH4/N2 separation materials, which means
that a conventional stainless-steel reactor can be used in the
industrial synthesis of this material. In addition, of TGA (Figures 2c,
2d and Table S1) shows that MIL-120Al exhibits higher thermal stability
(613 K) when compared to ATC-Cu (553 K)12 and
Ni(ina)2 (573 K).27