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Magnetic core-shell microspheres were developed to extract rare earth elements (REEs) from aqueous and brine solutions with up to 99.99% removal efficiency. The shell, composed of a thermally and chemically stable functionalized metal-organic framework (MOF), is grown over a synthesized Fe3O4 magnetic core (magnetite@MOF). The composite particles can be removed from the mixture under an applied magnetic field, offering a practical, and efficient REE-removal process. [ABSTRACT FROM AUTHOR]

Magnesite (MgCO3) precipitation within the nanoconfined space of adsorbed H2O films (∼5 monolayers) was determined to have an apparent activation energy of only 36 ± 6 kJ mol−1, suggesting that Mg2+ under nanoconfinement adopts a hydration configuration that mimics that of aqueous Ca2+, at least energetically, if not also specifically in hydration structure. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have proved to be very attractive for applications including gas storage, separation, sensing and catalysis. In particular, CO2 separation from flue gas in post-combustion processes is one of the main focuses of research among the scientific community. One of the major issues that are preventing the successful commercialization of these novel materials is their high affinity towards water that not only compromises gas sorption capacity but also the chemical stability. In this paper, we demonstrate a novel post-synthesis modification approach to modify MOFs towards increasing hydrophobic behaviour and chemical stability against moisture without compromising CO2 sorption capacity. Our approach consists of incorporating hydrophobic moieties on the external surface of the MOFs via physical adsorption. The rationale behind this concept is to increase the surface hydrophobicity in the porous materials without the need of introducing bulky functionalities inside the pore which compromises the sorption capacity toward other gases. We herein report preliminary results on routinely studied MOF materials [MIL-101(Cr) and NiDOBDC] demonstrating that the polymer-modified MOFs retain CO2 sorption capacity while reducing the water adsorption up to three times, with respect to the un-modified materials, via an equilibrium effect. Furthermore, the water stability of the polymer-functionalized MOFs is significantly higher than the water stability of the bare material. Molecular dynamic simulations demonstrated that this equilibrium effect implies a fundamental and permanent change in the water sorption capacity of MOFs. This approach can also be employed to render moisture stability and selectivity to MOFs that find applications in gas separations, catalysis and sensing where water plays a critical role in compromising MOF performance and recyclability. [ABSTRACT FROM AUTHOR]

The metal organic framework, MOF-74(Ni), was synthesized in a continuous flow microwave-assisted reactor obtaining a high space-time yield (~90 g h−1 L−1) and 96.5% conversion of reagents. Separation of the nucleation and growth steps was performed by using uniform and rapid microwave heating to induce nucleation, which allowed a substantial increase in conversion for shorter reaction times under mild pressure. High yields were achieved in minutes, as opposed to days for typical batch syntheses, with excellent control over the material's properties due to more uniform nucleation, and the separation of the nucleation and growth steps. Optimization of the microwave reactor parameters led to improvements in MOF-74(Ni) crystallinity, reagent conversion, and production rates. Differences in MOF-74(Ni) crystallinity were observed as smaller grains were formed when higher microwave zone temperatures were used. Crystallinity differences led to different final adsorption properties and surface areas. Herein we show that a continuous high space-time yield synthesis of MOF-74(Ni) allows control over nucleation using microwave heating. [ABSTRACT FROM AUTHOR]

A flexible metal–organic framework constructed from a flexible linker is shown to possess the capability of separating mixtures of polar compounds (propanol isomers) by exploiting the differences in the saturation capacities of the constituents. Transient breakthrough simulations show that these sorption-based separations are in favor of the component with higher saturation capacity. [ABSTRACT FROM AUTHOR]

Zeolite HOU-2 (LTA type) is prepared with the highest silica content (Si/Al = 2.1) reported for Na-LTA zeolites without the use of an organic structure-directing agent. The rational design of Si-rich zeolites has the potential to improve their thermal stability for applications in catalysis, gas storage, and selective separations. [ABSTRACT FROM AUTHOR]

In this study, we investigate the effect of water-cluster formation in the supercritical (SC) systems CO2/(H2O)nas a function of water content using DFT-based molecular dynamics simulations. The dependence of the intermolecular and intramolecular structure and dynamic properties upon water concentration in the supercritical CO2/H2O phase at a density of 0.74 g cm−3and temperature of 318.15 K is investigated in detail and compared to previous studies of the pure sc-CO2system, single D2O in sc-CO2, and Monte-Carlo simulations of a single water molecule in sc-CO2phase. Analysis of radial and orientational distribution functions of the intermolecular interactions shows that the presence of water molecules does not disturb the previously established distorted T-shaped orientation of CO2molecules, though there is evidence of perturbation of the second shell structure which enhances the preference for the slipped parallel orientation in this region. There is also evidence of short-lived hydrogen bonds between CO2and water molecules. For higher water concentrations, water clustering is observed, consistent with the low solubility of water in CO2under these conditions of temperature and pressure. Finally, the water–water and water–CO2interactions are discussed and analyzed in terms of the water self-association and thermodynamic quantities derived from the molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

A metal–organic framework obtained from a flexible organic linker shows a breathing phenomenon upon adsorption of saturated hydrocarbons. [ABSTRACT FROM AUTHOR]

We report the first Raman spectra of fully (18)O-labeled supercritical CO(2) (scCO(2)) and various isotopic mixtures. The experimental results, coupled with ab initio molecular dynamics calculations, demonstrate that the frequencies assigned to the Fermi dyad of the CO(2) molecule transpose upon isotopic labeling of both oxygen atoms. Although the transposition of the Fermi dyad of CO(2) gas due to isotopic substitution has been discussed before, this is the first confirmation of the effect in the Raman spectrum of the supercritical fluid and provides necessary groundwork for future Raman spectroscopy studies of reactions in this important medium. More importantly, the work yields a quantitative assessment of the mixing of states upon labeling that provides the needed clarification concerning the pedigree of the assignments for the dyad of CO(2) under supercritical conditions.

Cucurbit[7]uril (CB[7]), in its amorphous solid state, shows one of the highest CO(2) sorption capacities among known organic porous materials at 298 K and 0.1 and 1 bar. In addition to the highest CO(2) capacity, CB[7] also shows remarkable selectivity of CO(2) over N(2) and CH(4). These properties, along with the existence of readily available precursors, indicate amorphous CB[7] might find applications in recycling CO(2) particularly considering the easy synthesis and potentially low manufacturing costs.

In this study, we investigate the effect of water-cluster formation in the supercritical (SC) systems CO(2)/(H(2)O)(n) as a function of water content using DFT-based molecular dynamics simulations. The dependence of the intermolecular and intramolecular structure and dynamic properties upon water concentration in the supercritical CO(2)/H(2)O phase at a density of 0.74 g cm(-3) and temperature of 318.15 K is investigated in detail and compared to previous studies of the pure sc-CO(2) system, single D(2)O in sc-CO(2), and Monte-Carlo simulations of a single water molecule in sc-CO(2) phase. Analysis of radial and orientational distribution functions of the intermolecular interactions shows that the presence of water molecules does not disturb the previously established distorted T-shaped orientation of CO(2) molecules, though there is evidence of perturbation of the second shell structure which enhances the preference for the slipped parallel orientation in this region. There is also evidence of short-lived hydrogen bonds between CO(2) and water molecules. For higher water concentrations, water clustering is observed, consistent with the low solubility of water in CO(2) under these conditions of temperature and pressure. Finally, the water-water and water-CO(2) interactions are discussed and analyzed in terms of the water self-association and thermodynamic quantities derived from the molecular dynamics simulations.

Three interpenetrated metal-organic supramolecular isomers were synthesised using a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2), H(2) and methane at room temperature.

The uptake of various nitrogen oxides was studied with the well known nonporous p-tert-butylcalix[4]arene under ambient conditions.