Temperature dependent CO2 behavior in microporous 1-D channels of a metal-organic framework with multiple interaction sites

Molecular CO2 Storage: State of a Single-Molecule Gas

CO2 evolution is one of the urgent global issues; meanwhile, understanding of sorptive/dynamic behavior is crucial to create next-generation encapsulant materials with stable sorbent processes. Herein, we showcase molecular CO2 storage constructed by a [60]fullerenol nanopocket. The CO2 density reaches 2.401 g/cm3 within the nanopore, showing strong intramolecular interactions, which induce nanoconfinement effects such as forbidden translation, restricted rotation, and perturbed vibration of CO2. We also disclosed an equation of state for a molecular CO2 gas, revealing a very low pressure of 3.14 rPa (1 rPa = 10-27 Pa) generated by the rotation/vibration at 300 K. Curiously enough, the CO2 capture enabled to modulate an external property of the encapulant material itself, i.e., association of the [60]fullerenol via intercage hydrogen-bonding.

Gating effect for gas adsorption in microporous materials-mechanisms and applications

In the past two decades, various microporous materials have been developed as useful adsorbents for gas adsorption for a wide range of industries. Considerable efforts have been made to regulate the pore accessibility in microporous materials for the manipulation of guest molecules' admission and release. It has long been known that some microporous adsorbents suddenly become highly accessible to guest molecules at specific conditions, e.g., above a threshold pressure or temperature. This anomalous adsorption behavior results from a gating effect, where a structural variation of the adsorbent leads to an abrupt change in the gas admission. This review summarizes the mechanisms of the gating effect, which can be a result of the deformation of the framework (e.g., expansion, contraction, reorientation, and sliding of the unit cells), the vibration of the pore-keeping groups (e.g., rotation, swing, and collapse of organic linkers), and the oscillation of the pore-keeping ions (e.g. cesium, potassium, etc.). These structural variations are induced either by the host-guest interaction or by an external stimulus, such as temperature or light, and account for the gating effect at a threshold value of the stimulus. Emphasis is given to the temperature-regulated gating effect, where the critical admission temperature is dictated by the combined effect of the gate opening and thermodynamic factors and plays a key role in regulating guest admission. Molecular simulations can improve our understanding of the gate opening/closing transitions at the atomic scale and enable the construction of quantitative models to describe the gated adsorption behaviour at the macroscale level. The gating effect in porous materials has been widely applied in highly selective gas separation and offers great potential for gas storage and sensing.

Partial and Complete Substitution of the 1,4-Benzenedicarboxylate Linker in UiO-66 with 1,4-Naphthalenedicarboxylate: Synthesis, Characterization, and H2-Adsorption Properties

We describe the synthesis and corresponding full characterization of the set of UiO-66 metal-organic frameworks (MOFs) with 1,4-benzenedicarboxylate (C₆H₄(COOH)₂, hereafter H₂BDC) and 1,4-naphthalenedicarboxylate (C₁₀H₆(COOH)₂, hereafter H₂NDC) mixed linkers with NDC contents of 0, 25, 50, and 100%. Their structural (powder X-ray diffraction, PXRD), adsorptive (N₂, H₂, and CO₂), vibrational (IR/Raman), and thermal stability (thermogravimetric analysis, TGA) properties quantitatively correlate with the NDC content in the material. The UiO-66 phase topology is conserved at all relative fractions of BDC/NDC. The comparison between the synchrotron radiation PXRD and 77 K N₂-adsorption isotherms obtained on the 50:50 BDC/NDC sample and on a mechanical mixture of the pure BDC and NDC samples univocally proves that in the mixed linkers of the MOFs the BDC and NDC linkers are shared in each MOF crystal, discarding the hypothesis of two independent phases, where each crystal contains only BDC or NDC linkers. The careful tuning of the NDC content opens a way for controlled alteration of the sorption properties of the resulting material as testified by the H₂-adsorption experiments, showing that the relative ranking of the materials in H₂ adsorption is different in different equilibrium-pressure ranges: at low pressures, 100NDC is the most efficient sample, while with increasing pressure, its relative performance progressively declines; at high pressures, the ranking follows the BDC content, reflecting the larger internal pore volume available in the MOFs with a higher fraction of smaller linkers. The H₂-adsorption isotherms normalized by the sample Brunauer-Emmett-Teller specific surface area show, in the whole pressure range, that the surface-area-specific H₂-adsorption capabilities in UiO-66 MOFs increase progressively with increasing NDC content. Density functional theory calculations, using the hybrid B3LYP exchange correlation functional and quadruple-ζ with four polarization functions (QZ4P) basis set, show that the interaction of H₂ with the H₂NDC linker results in an adsorption energy larger by about 15% with respect to that calculated for adsorption on the H₂BDC linker.

CFA-15 – a perfluorinated metal–organic framework with linear 1-D CuII-chains containing accessible unsaturated, reactive metal centres

The synthesis and crystal structure of the perfluorinated metal–organic framework CFA-15, CuII3(tfpc)₂(OH)₂·DMF, and the organic ligand H₂-tfpc, 3,5-bis(trifluoromethyl)-1H-pyrazole-4-carboxylic acid, are described.

Selective carbon dioxide sorption by a new breathing three-dimensional Zn-MOF with Lewis basic nitrogen-rich channels

A CO₂ selective dynamic three-dimensional MOF, [Zn₂(μ₄-3,3′-PDBA)₂(μ₂-bpa)]₃·(DMF)₅(H₂O)₁₃, shows an unusual 3(2 + 1)-fold interpenetrated structure and phenomenal hysteretic behavior in CO₂ sorption.