SO₂ Capture by Two Aluminum-Based MOFs: Rigid-like MIL-53(Al)-TDC versus Breathing MIL-53(Al)-BDC

Abstract

Metal−organic frameworks MIL-53(Al)-TDC and MIL-53(Al)-BDC were explored in the SO 2 adsorption process. MIL-53(Al)-TDC was shown to behave as a rigid-like material upon SO 2 adsorption. On the other hand, MIL-53(Al)-BDC exhibits guest-induced flexibility of the framework with the presence of multiple steps in the SO 2 adsorption isotherm that was related through molecular simulations to the existence of three different pore opening phases narrow pore, intermediate pore, and large pore. Both materials proved to be exceptional candidates for SO 2 capture, even under wet conditions, with excellent SO 2 adsorption, good cycling, chemical stability, and easy regeneration. Further, we propose MIL-53(Al)-TDC and MIL-53(A)-BDC of potential interest for SO 2 sensing and SO 2 storage/transportation, respectively.

Unravelling gas sorption in the aluminum metal‐organic framework CAU‐23: CO2, H2, CH4, SO2 sorption isotherms, enthalpy of adsorption and mixed‐adsorptive calculations

“…Figure 9 compares the SO 2 uptake data of CAU-23 with other Al-MOFs at 1 bar and 293 K. [38,[58][59][60] A similar uptake is found for MIL-53-TDC. The MOFs MIL-53 and MIL-100, both having a higher specific surface area and pore volume (Table S6), have significantly higher SO 2 uptakes.…”

“…Figure 9 compares the SO 2 uptake data of CAU‐23 with other Al‐MOFs at 1 bar and 293 K [38,58–60] . A similar uptake is found for MIL‐53‐TDC.…”

“…For uptake data at other temperatures and the uptake in cm 3 g À 1 or wt-% see Table S11 in SI. [55,54,51] [38] MIL-160, [59] CAU-10-H, [38] MIL-53, [60] MIL-53-TDC, [60] and MIL-100 [38] ). For uptake data at other temperatures and the uptake in cm 3 g À 1 or wt-% see Table S12 in SI.…”

“… Comparison of SO 2 uptake of CAU‐23 (shaded area) with selected Al‐MOFs (grey) at 293 K and 1 bar (Alfum, [38] MIL‐160, [59] CAU‐10‐H, [38] MIL‐53, [60] MIL‐53‐TDC, [60] and MIL‐100 [38] ). For uptake data at other temperatures and the uptake in cm 3 g −1 or wt‐% see Table S12 in SI [38] …”

Gate Opening without Volume Change Triggers Cooperative Gas Interactions, Underpins an Isotherm Step in Metal–Organic Frameworks

“…Two or more steps in gas adsorption isotherms in MOFs can also result from condensation of adsorbate molecules within their pores. , Some MOFs exhibit a “breathing” or “gate-opening” phenomenon which also leads to steps in the isotherm. A porous material is said to breathe when a pronounced structural transformation results in increase or decrease of pore volume. , Breathing might result either from increased pore volume upon a structural transition in the MOF, resulting in additional gas uptake − or due to other external stimuli. ,− While a transition in the MOF structure during gas adsorption will necessarily lead to a step in the isotherm, the converse need not be true. It is possible to observe a step in the isotherm without any observable structural change.…”