Kinetics of Guest-Induced Structural Transitions in Metal–Organic-Framework MIL-53(Al)-NH₂ Probed by High-Pressure Nuclear Magnetic Resonance

Abstract

A nuclear magnetic resonance (NMR) study of a pore opening in amino-functionalized metal−organic framework (MOF) MIL-53(Al) in response to methane pressure variation is presented. Variations of both NMR signal intensities and transversal relaxation rates for methane are found to reveal hysteretic structural transitions in the MOF material, which are smeared out over broad pressure ranges. Experiments with pressure reversals upon an incomplete adsorption/desorption gave deeper insight into the microscopic transition mechanisms. These experiments have unequivocally proven that the non-stepwise pore opening/closing transitions observed in the experiments are governed by a distribution of the opening/closing pressures over different MOF crystallites, for example, due to a distribution of the crystal sizes or shapes. The slow kinetics of the structural transitions measured in the hysteresis regime revealed a complex free energy landscape for the phase transition process.

Optical chemosensors based on metal organic frameworks for selective detection of hazardous pollutants: A review

“…Universitetet i Oslo UiO-66 Zr (BDC) 1,4-benzenedicarboxylic acid [30][31][32] UiO-67 Zr (BPDC) biphenyl-4,4'dicarboxylate [30][31][32][33] UiO-68 Zr (TPDC) 1':4',1terphenyl-3,3'dicarboxylate [34][35][36] UiO-abdc Zr (abdc) (BDC-NH2) 2-amino-1,4benzenediacarboxylic acid [42,43] MIL-88B-Fe Fe (BDC) 1,4-benzenedicarboxylic acid [44] MIL-88B-4CH3 Fe (BDC-Me2) 2,5 dimethyl-1,4-benzenedicarboxylic acid [45] MIL-100-Fe Fe (BTC) benzene-1,3,5tricarboxylate [46,47] MIL-101 Cr (BDC) 1,4-benzenedicarboxylic acid [48] MIL-140 Ce (BDC) Solvothermal method, (4) Microwave method, (5) Sono-chemical synthesis method, (6) Electrochemical synthesis method, (7) Iono-thermal process method, (8) Mechanochemical method [71] .…”

Terahertz Spectroscopy Unambiguously Determines the Orientation of Guest Water Molecules in a Structurally Elusive Metal–Organic Framework

“…At room temperature, it undergoes a reversible transition from the large-pore to the narrow-pore phase through a breathing effect by adsorption of water molecules into the framework, ,, causing a significant volume fluctuation of up to 40%. This absorption-influenced transition is not limited to water alone, as other guest molecules, including CH 4 , N 2 , CO, and O 2 , have been shown to initiate a similar effect. − Additionally, the stability of MIL-53­(Al) under high mechanical stress has also been noted, as it has been reported to undergo a pressure-induced phase transition from its large-pore form to the narrow-pore form at high pressures suggesting its suitability as a nanoshock absorber . Further, MIL-53­(Al) is environmentally and biologically friendly. − Overall, the interesting guest-induced framework dynamics in MIL-53­(Al) are important to understand from a fundamental standpoint, in order to further design and tune the adsorption behavior of host–guest complexes, and this represents a model system for studying the broader class of flexible MOFs.…”

“…This absorption-influenced transition is not limited to water alone, as other guest molecules, including CH 4 , N 2 , CO, and O 2 , have been shown to initiate a similar effect. 27 − 29 Additionally, the stability of MIL-53(Al) under high mechanical stress has also been noted, 30 as it has been reported to undergo a pressure-induced phase transition from its large-pore form to the narrow-pore form at high pressures suggesting its suitability as a nanoshock absorber. 23 Further, MIL-53(Al) is environmentally and biologically friendly.…”

NMR Relaxation of Gas Adsorbed in Microporous Material

“…Owing to these merits, this technique has already been widely used in research and industry to study the fluid confined in porous media such as reservoir rocks, construction materials, and foods. ,, However, the traditional NMR relaxation theories for confined fluids may not apply to gas adsorption in a microporous material. It has been observed that the NMR relaxation times T 1 and T 2 of gas confined in micropores can be higher than the bulk phase, , which contradicts the traditional theories predicting that confined fluids always relax faster. , There is still a lack of a quantitative explicit model for NMR relaxation of gas adsorbed in microporous material, so although NMR relaxometry has been used to study the adsorption capacity, ,, molecular movement, − and pore structure of multiple gas adsorption systems, the information that can be extracted from the results is limited.…”