RESUMO
Herein, a robust microporous aluminum tetracarboxylate framework, MIL-120(Al)-AP, (MIL, AP: Institute Lavoisier and Ambient Pressure synthesis, respectively) is reported, which exhibits high CO2 uptake (1.9 mmol g-1 at 0.1 bar, 298 K). In situ Synchrotron X-ray diffraction measurements together with Monte Carlo simulations reveal that this structure offers a favorable CO2 capture configuration with the pores being decorated with a high density of µ2-OH groups and accessible aromatic rings. Meanwhile, based on calculations and experimental evidence, moderate host-guest interactions Qst (CO2) value of MIL-120(Al)-AP (-40 kJ mol-1) is deduced, suggesting a relatively low energy penalty for full regeneration. Moreover, an environmentally friendly ambient pressure green route, relying on inexpensive raw materials, is developed to prepare MIL-120(Al)-AP at the kilogram scale with a high yield while the Metal- Organic Framework (MOF) is further shaped with inorganic binders as millimeter-sized mechanically stable beads. First evidences of its efficient CO2/N2 separation ability are validated by breakthrough experiments while operando IR experiments indicate a kinetically favorable CO2 adsorption over water. Finally, a techno-economic analysis gives an estimated production cost of ≈ 13 $ kg-1, significantly lower than for other benchmark MOFs. These advancements make MIL-120(Al)-AP an excellent candidate as an adsorbent for industrial-scale CO2 capture processes.
RESUMO
The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- µ-OH-connected corner-sharing AlO4(OH)2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers, and cis-µ-OH-connected corner-sharing AlO4(OH)2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc has a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P0 ≈ 0.5 in MIL-53-muc, to P/P0 ≈ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo reveal that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations show that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60 °C, outperforming benchmark sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air.
RESUMO
The origin of the glass transition is still an open debate, especially for the new class of glasses, formed from metal-organic compounds. High-temperature in situ 2H Nuclear Magnetic Resonance (NMR) experiments are performed on deuterated samples of ZIF-62 (Zn(C3H4N2)2-x(C7H6N2)x, with x = 0.25 and x = 0.05), the prototypical metal-organic framework glass former. Using lineshape analysis, frequencies and angular amplitudes of oscillations of the imidazolate ring during heating up to the melt progressively increasing from ≈10 to 150 MHz, and from ≈5° to 25° are found. This behavior is compositionally dependent and points to the origin of the glass transition lying in organic linker movement, in a similar vein to that witnessed in some organics and contrary to the purely inorganic-based view of Metal-Organic Framework (MOF) glasses taken to date. This experimental approach shows the potential to elucidate the melting and/or decomposition process for a wide range of MOFs.
RESUMO
Al-based cationic metal-organic frameworks (MOFs) are uncommon. Here, we report a cationic Al-MOF, MIP-213(Al) ([Al18(µ2-OH)24(OH2)12(mdip)6]6Cl·6H2O) constructed from flexible tetra-carboxylate ligand (5,5'-Methylenediisophthalic acid; H4mdip). Its crystal structure was determined by the combination of three-dimensional electron diffraction (3DED) and high-resolution powder X-ray diffraction. The structure is built from infinite corner-sharing chains of AlO4(OH)2 and AlO2(OH)3(H2O) octahedra forming an 18-membered rings honeycomb lattice, similar to that of MIL-96(Al), a scarce Al-polycarboxylate defective MOF. Despite sharing these structural similarities, MIP-213(Al), unlike MIL-96(Al), lacks the isolated µ3-oxo-bridged Al-clusters. This leads to an ordered defective cationic framework whose charge is balanced by Cl- sandwiched between two Al-trimers at the corner of the honeycomb, showing strong interaction with terminal H2O coordinated to the Al-trimers. The overall structure is endowed by a narrow quasi-1D channel of dimension ~4.7 Å. The Cl- in the framework restrains the accessibility of the channels, while the MOF selectively adsorbs CO2 over N2 and possesses high hydrolytic stability.