Negative gas adsorption transitions and pressure amplification phenomena in porous frameworks.

Nanoporous solids offer a wide range of functionalities for industrial, environmental, and energy applications. However, only a limited number of porous materials are responsive, the nanopore dynamically alters its size and shape in response to external stimuli such as temperature, pressure, light or the presence of specific molecular stimuli adsorbed inside the voids deforming the framework. Adsorption-induced structural deformation of porous solids can result in unique counterintuitive phenomena.

Unraveling the influence of surface functionalities on gas Physisorption: A comprehensive study on SBA-15 nanoporous material from Monte Carlo simulation for improved Textural-Energetic characterization.

In this study, we conducted experimental and Monte Carlo simulation studies in the grand canonical ensemble (GCMC) to investigate the role of molecular orientation and surface heterogeneity on the adsorption of N at 77 K. Our research focused on a series of ordered nanoporous materials (SBA-15) with varying degrees of oxygen functionalities. Specifically, we examined the effects of surface heterogeneity on the calculation of pore size distribution (PSD) and the Brunauer-Emmett-Teller (BET) area of porous materials.

Benchtop Measurement of Full Adsorption Isotherms by NMR.

Physisorption using gas or vapor probe molecules is the most common characterization technique for porous materials. The method provides textural information on the adsorbent as well as the affinity for a specific adsorbate, typically through equilibrium pressure measurements. Here, we demonstrate how low-field NMR can be used to measure full adsorption isotherms, and how by selectively measuring H spins of the adsorbed probe molecules, rather than those in the vapor phase, this "NMR-relaxorption" technique provides insights about local dynamics beyond what can be learned from physisorption alone.

Low Temperature Calorimetry Coupled with Molecular Simulations for an In-Depth Characterization of the Guest-Dependent Compliant Behavior of MOFs.

In this study adsorption microcalorimetry is employed to monitor the adsorption of four probes (argon, oxygen, nitrogen, and carbon monoxide) on a highly flexible mesoporous metal-organic framework (DUT-49, DUT = Dresden University of Technology), precisely measuring the differential enthalpy of adsorption alongside high-resolution isotherms. This experimental approach combined with force field Monte Carlo simulations reveals distinct pore filling adsorption behaviors for the selected probes, with argon and oxygen showing abrupt adsorption in the open pore form of DUT-49, in contrast with the gradual filling for nitrogen and carbon monoxide. A complex structural transition behavior of DUT-49 observed upon nitrogen adsorption is elucidated through an isotherm deconvolution in order to quantify the fractions of the open pore, contracted pore, and intermediate pore forms that coexist at a given gas pressure.

Tailoring the separation properties of flexible metal-organic frameworks using mechanical pressure.

Metal-organic frameworks are widely considered for the separation of chemical mixtures due to their adjustable physical and chemical properties. However, while much effort is currently devoted to developing new adsorbents for a given separation, an ideal scenario would involve a single adsorbent for multiple separations. Porous materials exhibiting framework flexibility offer unique opportunities to tune these properties since the pore size and shape can be controlled by the application of external stimuli.

Large and tunable magnetocaloric effect in gadolinium-organic framework: tuning by solvent exchange.

Magnetic properties of three variants of MOF-76(Gd), {[Gd(BTC)(HO)]·G} (BTC = benzene-1,3,5-tricarboxylate, G = guest molecules) were investigated by static susceptibility, isothermal magnetization and specific heat capacity measurements. In the study we used as synthesized MOF-76(Gd)-DMF (1) (G = DMF = dimethylformamide), containing DMF molecules in the cavity system, compound MOF-76(Gd) (2), activated complex without solvents in the cavities and water exchanged sample MOF-76(Gd)-HO (3). A pronounced change in the magnetic entropy was found near the critical temperature for all three compounds.

Vapor-Phase Linker Exchange of the Metal-Organic Framework ZIF-8: A Solvent-Free Approach to Post-synthetic Modification.

Zeolitic imidazolate frameworks (ZIFs) are a sub-class of metal-organic frameworks (MOFs). Although generally stable, ZIFs can undergo post-synthetic linker exchange (PSLE) in solution under mild conditions. Herein, we present a novel, solvent-free approach to post-synthetic linker exchange through exposure to linker vapor.

Metal-organic framework crystal-glass composites.

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix.

Investigating the effect of alumina shaping on the sorption properties of promising metal-organic frameworks.

Three promising MOF candidates, UiO-66(Zr), MIL-100(Fe) and MIL-127(Fe) are shaped through granulation with a ρ-alumina binder. Subsequently, changes in the surface characteristics and adsorption performance are evaluated through adsorption microcalorimetry at 303 K with several common probes (N, CO, CO, CH, CH, CH, CH and CH), generating a detailed picture of adsorbate-adsorbent interactions. Vapour adsorption experiments with water and methanol were further used to gauge changes in hydrophobicity caused by the addition of the alumina binder.

Adsorption Contraction Mechanics: Understanding Breathing Energetics in Isoreticular Metal-Organic Frameworks.

A highly porous metal-organic framework DUT-48, isoreticular to DUT-49, is reported with a high surface area of 4560 m·g and methane storage capacity up to 0.27 g·g (164 cm·cm) at 6.5 MPa and 298 K.

Synthesis of ZIF-93/11 Hybrid Nanoparticles via Post-Synthetic Modification of ZIF-93 and Their Use for H /CO Separation.

The present work shows the synthesis of nano-sized hybrid zeolitic imidazolate frameworks (ZIFs) with the rho topology based on a mixture of the linkers benzimidazole (bIm) and 4-methyl-5-imidazolecarboxaldehyde (4-m-5-ica). The hybrid ZIF was obtained by post-synthetic modification of ZIF-93 in a bIm solution. The use of different solvents, MeOH and N,N-dimethylacetamide (DMAc), and reaction times led to differences in the quantity of bIm incorporated to the framework, from 7.

Metal-Organic Frameworks as Catalyst Supports: Influence of Lattice Disorder on Metal Nanoparticle Formation.

Because of their high tunability and surface area, metal-organic frameworks (MOFs) show great promise as supports for metal nanoparticles. Depending on the synthesis route, MOFs may contain defects. Here, we show that highly crystalline MIL-100(Fe) and disordered Basolite® F300, with identical iron 1,3,5-benzenetricarboxylate composition, exhibit very divergent properties when used as a support for Pd nanoparticle deposition.

Microporous Lead-Organic Framework for Selective CO Adsorption and Heterogeneous Catalysis.

A novel microporous metal-organic framework, {[Pb(μ-MTB)(HO)]·5DMF·HO} (1; MTB = methanetetrabenzoate and DMF = N,N'-dimethylformamide), was successfully synthesized by a solvothermal reaction and structurally characterized by single-crystal X-ray diffraction. The framework exhibits a unique tetranuclear [Pb(μ-COO)(μ-COO)(COO)(HO)] secondary building unit (SBU). The combination of the SBU with the tetrahedral symmetry of MTB results in a three-dimensional network structure, with one-dimensional jarlike cavities having sizes of about 14.

Investigating Unusual Organic Functional Groups to Engineer the Surface Chemistry of Mesoporous Silica to Tune CO-Surface Interactions.

As the search for functionalized materials for CO capture continues, the role of theoretical chemistry is becoming more and more central. In this work, a strategy is proposed where ab initio calculations are compared and validated by adsorption microcalorimetry experiments for a series of, so far unexplored, functionalized SBA-15 silicas with different spacers (aryl, alkyl) and terminal functions (N, NO). This validation then permitted to propose the use of a nitro-indole surface functionality.

Modeling of adsorption of CO in the deformed pores of MIL-53(Al).

Molecular simulations were performed to predict CO adsorption in flexible metal-organic frameworks (MOFs). A generic force field was fitted to our experimental data to describe the non-bonded (electrostatic and van der Waals) interactions between CO molecules and the large pore (lp) and narrow pore (np) forms of the MIL-53(Al) framework. With the new validated force field, it is possible to predict CO uptake and enthalpy of adsorption at various applied external pressures that will modify the structure's pore configuration and allow us to have more control over the adsorption/desorption process.

Screening the Effect of Water Vapour on Gas Adsorption Performance: Application to CO Capture from Flue Gas in Metal-Organic Frameworks.

A simple laboratory-scale protocol that enables the evaluation of the effect of adsorbed water on CO uptake is proposed. 45 metal-organic frameworks (MOFs) were compared against reference zeolites and active carbons. It is possible to classify materials with different trends in CO uptake with varying amounts of pre-adsorbed water, including cases in which an increase in CO uptake is observed for samples with a given amount of pre-adsorbed water.

Influence of Solvent-Like Sidechains on the Adsorption of Light Hydrocarbons in Metal-Organic Frameworks.

A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal-organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low-density solvent with restricted degrees of freedom, offer tunable control of dispersive host-guest interactions.