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Injecting fluids into deep underground geologic structures is a critical component to development of long-term strategies for managing greenhouse gas emissions and facilitating energy extraction operations. Recently, we reported that metal–organic frameworks are low-frequency, absorptive-acoustic metamaterial that may be injected into the subsurface to enhance geophysical monitoring tools used to track fluids and map complex structures. A key requirement for this nanotechnology deployment is transportability through porous geologic media without being retained by mineral-fluid interfaces. We used flow-through column studies to estimate transport and retention properties of five different polymer-coated MIL-101(Cr) nanoparticles (NP) in siliceous porous media. When negatively charged polystyrene sulfonate coated nanoparticles (NP-PSS-70K) were transported in 1 M NaCl, only about 8.4% of nanoparticles were retained in the column. Nanoparticles coated with polyethylenimine (NP-PD1) exhibited significant retention (> 50%), emphasizing the importance of complex nanoparticle-fluid-rock interactions for successful use of nanofluid technologies in the subsurface. Nanoparticle transport experiments revealed that nanoparticle surface characteristics play a critical role in nanoparticle colloidal stability and as well the transport. [ABSTRACT FROM AUTHOR]

Adsorption‐based cooling is an energy‐efficient renewable‐energy technology that can be driven using low‐grade industrial waste heat and/or solar heat. Here, we report the first exploration of fluorocarbon adsorption using porous covalent organic polymers (COPs) for this cooling application. High fluorocarbon R134a equilibrium capacities and unique overall linear‐shaped isotherms are revealed for the materials, namely COP‐2 and COP‐3. The key role of mesoporous defects on this unusual adsorption behavior was demonstrated by molecular simulations based on atomistic defect‐containing models built for both porous COPs. Analysis of simulated R134a adsorption isotherms for various defect‐containing atomistic models of the COPs shows a direct correlation between higher fluorocarbon adsorption capacities and increasing pore volumes induced by defects. Combined with their high porosities, excellent reversibility, fast kinetics, and large operating window, these defect‐containing porous COPs are promising for adsorption‐based cooling applications. [ABSTRACT FROM AUTHOR]

Adsorption‐based cooling is an energy‐efficient renewable‐energy technology that can be driven using low‐grade industrial waste heat and/or solar heat. Here, we report the first exploration of fluorocarbon adsorption using porous covalent organic polymers (COPs) for this cooling application. High fluorocarbon R134a equilibrium capacities and unique overall linear‐shaped isotherms are revealed for the materials, namely COP‐2 and COP‐3. The key role of mesoporous defects on this unusual adsorption behavior was demonstrated by molecular simulations based on atomistic defect‐containing models built for both porous COPs. Analysis of simulated R134a adsorption isotherms for various defect‐containing atomistic models of the COPs shows a direct correlation between higher fluorocarbon adsorption capacities and increasing pore volumes induced by defects. Combined with their high porosities, excellent reversibility, fast kinetics, and large operating window, these defect‐containing porous COPs are promising for adsorption‐based cooling applications. [ABSTRACT FROM AUTHOR]

The interactions of CO2/H2 with p-tert-butylcalix[4]arene (TBC4) were studied using potential of mean force (PMF) and free energy perturbation approaches. To the best of our knowledge, the present work is one of the first to employ the constrained mean force approach to evaluate solute selectivity by the TBC4 molecule. The computed PMFs for the interaction of CO2/H2 with a single TBC4 molecule establish that the interaction of CO2 with the open end of the cage structure is attractive while the interaction with H2 is repulsive. Free energy perturbation calculations were performed for the same two guest molecules with a pair of facing TBC4 molecules used as a representative model as found in the TBC4 molecular solid. At low temperature, both CO2/H2 have favorable interactions with the TBC4 pair, with the CO2 interaction being considerably greater. These results are in agreement with recent experimental data showing considerable CO2 uptake by TBC4 at moderate pressures. [ABSTRACT FROM AUTHOR]

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]

The oxygen electrode plays a vital role in the successful commercialization of renewable energy technologies, such as fuel cells and water electrolyzers. In this study, the Prussian blue analogue-derived nitrogen-doped nanocarbon (NC) layer-trapped, cobalt-rich, core-shell nanostructured electrocatalysts (core-shell Co@NC) are reported. The electrode exhibits an improved oxygen evolution activity and stability compared to that of the commercial noble electrodes. The core-shell Co@NC-loaded nickel foam exhibits a lower overpotential of 330 mV than that of IrO2 on nickel foam at 10 mA cm-2 and has a durability of over 400 h. The commercial Pt/C cathode-assisted, core-shell Co@NC-anode water electrolyzer delivers 10 mA cm-2 at a cell voltage of 1.59 V, which is 70 mV lower than that of the IrO2-anode water electrolyzer. Over the long-term chronopotentiometry durability testing, the IrO2-anode water electrolyzer shows a cell voltage loss of 230 mV (14%) at 95 h, but the loss of the core-shell Co@NC-anode electrolyzer is only 60 mV (4%) even after 350 h cell-operation. The findings indicate that the Prussian blue analogue is a class of inorganic nanoporous materials that can be used to derive metal-rich, core-shell electrocatalysts with enriched active centers. [ABSTRACT FROM AUTHOR]

The mixed-metal strategy, by which a MOF framework with two different metal nodes was prepared, was utilized with MOF-74 for potential adsorption chiller applications. The Ni salt precursor was partially replaced during synthesis with the relatively inexpensive Zn salt. The bimetallic MOF-74 containing only a fraction of Ni was shown to provide efficient H2O adsorption performance, while utilizing the more inexpensive Zn salt thus significantly mitigated the material costs of industrial scale synthesis/applications. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have recently attracted enormous interest over the past few years in energy storage and gas separation, yet there have been few reports for adsorption cooling applications. Adsorption cooling technology is an established alternative to mechanical vapor compression refrigeration systems and is an excellent alternative in industrial environments where waste heat is available. We explored the use of MOFs that have very high mass loading and relatively low heats of adsorption, with certain combinations of refrigerants to demonstrate a new type of highly efficient adsorption chiller. Computational fluid dynamics combined with a system level lumped-parameter model have been used to project size and performance for chillers with a cooling capacity ranging from a few kW to several thousand kW. These systems rely on stacked micro/mini-scale architectures to enhance heat and mass transfer. Recent computational studies of an adsorption chiller based on MOFs suggests that a thermally-driven coefficient of performance greater than one may be possible, which would represent a fundamental breakthrough in performance of adsorption chiller technology. Presented herein are computational and experimental results for hydrophyilic and fluorophilic MOFs. [ABSTRACT FROM PUBLISHER]

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]

Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure-directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic-free syntheses of two polymorphs of the small-pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H2O relative to other light gases (e.g., H2, N2, CO2). Our findings refute prior theoretical studies postulating that GIS-type zeolites are excellent materials for CO2 separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS-type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis. [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]

Crystalline metal organic framework (MOF) materials containing interconnected porosity can be chemically modified to promote stimulus-driven (light, magnetic or electric fields) structural transformations that can be used in a number of devices. Innovative research strategies are now focused on understanding the role of chemical bond manipulation to reversibly alter the free volume in such structures of critical importance for electro-catalysis, molecular electronics, energy storage technologies, sensor devices and smart membranes. In this letter, we study the mechanism for which an electrically switchable MOF composed of Cu(TCNQ) (TCNQ = 7,7,8,8-tetracyanoquinodimethane) transitions from a high-resistance state to a conducting state in a reversible fashion by an applied potential. The actual mechanism for this reversible electrical switching is still not understood even though a number of reports are available describing the application of electric-field-induced switching of Cu(TCNQ) in device fabrication. [ABSTRACT FROM AUTHOR]

In this review, we describe recent efforts to systematically study nano-structured metal organic frameworks (MOFs), also known as metal organic heat carriers, with particular emphasis on their application in heating and cooling processes. We used both molecular dynamics and grand canonical Monte Carlo simulation techniques to gain a molecular-level understanding of the adsorption mechanism of gases in these porous materials. We investigated the uptake of various gases such as refrigerants R12 and R143a. We also evaluated the effects of temperature and pressure on the uptake mechanism. Our computed results compared reasonably well with available measurements from experiments, thus validating our potential models and approaches. In addition, we investigated the structural, diffusive and adsorption properties of different hydrocarbons in Ni2(dhtp). Finally, to elucidate the mechanism of nanoparticle dispersion in condensed phases, we studied the interactions among nanoparticles in various liquids, such asn-hexane, water and methanol. [ABSTRACT FROM PUBLISHER]

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]

Presents an interfacial area ratio (IAR) model for the prediction of diffusion coefficients as a function of the degree of water saturation. Definition of tortuosity factor in the IAR model; Factor that affects diffusion behavior in unsaturated media; Diffusion coefficients for conservative solutes as a function of water content.

Adsorption cooling, structure defects, fluorocarbon refrigerants, porous covalent organic polymers Keywords: adsorption cooling; structure defects; fluorocarbon refrigerants; porous covalent organic polymers EN adsorption cooling structure defects fluorocarbon refrigerants porous covalent organic polymers 17894 17894 1 08/05/21 20210809 NES 210809 B Defekthaltige kovalente organische Polymere b sind vielversprechend für adsorptionsbasierte Kühlanwendungen. Innentitelbild: Porous Covalent Organic Polymers for Efficient Fluorocarbon-Based Adsorption Cooling (Angew. [Extracted from the article]

In their Research Article on page 18037, Guillaume Maurin, Radha Kishan Motkuri, and co-workers present experimental and computational evidence that mesoporous defects in the framework play a key role for the unique overall linear-shaped R134a adsorption isotherm and the exceptional adsorption uptake. Inside Cover: Porous Covalent Organic Polymers for Efficient Fluorocarbon-Based Adsorption Cooling (Angew. Keywords: adsorption cooling; structure defects; fluorocarbon refrigerants; porous covalent organic polymers EN adsorption cooling structure defects fluorocarbon refrigerants porous covalent organic polymers 17750 17750 1 08/05/21 20210809 NES 210809 B Defective covalent organic polymers b are promising for adsorption-based cooling applications. [Extracted from the article]

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

The improvement in adsorption/desorption of hydrofluorocarbons has implications for many heat transformation applications such as cooling, refrigeration, heat pumps, power generation, etc. The lack of chlorine in hydrofluorocarbons minimizes the lasting environmental damage to the ozone, with R134a (1,1,1,2-tetrafluoroethane) being used as the primary industrial alternative to commonly used Freon-12. The efficacy of novel adsorbents used in conjunction with R134a requires a deeper understanding of the host-guest chemical interaction. Metal-organic frameworks (MOFs) represent a newer class of adsorbent materials with significant industrial potential given their high surface area, porosity, stability, and tunability. In this work, we studied two benchmark MOFs, a microporous Ni-MOF-74 and mesoporous Cr-MIL-101. We employed a combined experimental and simulation approach to study the adsorption of R134a to better understand host-guest interactions using equilibrium isotherms, enthalpy of adsorption, Henry's coefficients, and radial distribution functions. The overall uptake was shown to be exceptionally high for Cr-MIL-101, >140 wt% near saturation while >50 wt% at very low partial pressures. For both MOFs, simulation data suggest that metal sites provide preferable adsorption sites for fluorocarbon based on favorable C-F ··· M+ interactions between negatively charged fluorine atoms of R134a and positively charged metal atoms of the MOF framework. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs); also known as porous coordination polymers (PCP) are a class of porous crystalline materials constructed by connecting metal clusters via organic linkers. The possibility of functionalization leads to virtually infinite MOF designs using generic modular methods. Functionalized MOFs can exhibit interesting physical and chemical properties including accelerated adsorption kinetics and catalysis. Although there are discrete methods to synthesize well-defined nanoscale MOFs, rapid and flexible methods are not available for continuous, one-pot synthesis and post-synthetic modification (functionalization) of MOFs. Here, we show a continuous, scalable nanodroplet-based microfluidic route that not only facilitates the synthesis of MOFs at a nanoscale, but also offers flexibility for direct functionalization with desired functional groups (e.g., -COCH3, fluorescein isothiocyanate; FITC). In addition, the presented route of continuous manufacturing of functionalized nanosized MOFs takes significantly less time compared to state-of-the-art batch methods currently available (1 hr vs. several days). We envisage our approach to be a breakthrough method for synthesizing complex functionalized nanomaterials (metal, metal oxides, quantum dots and MOFs) that are not accessible by direct batch processing and expand the range of a new class of functionalized MOF-based functional nanomaterials. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue are the groups of R. K. Motkuri and J. D. Rimer at the Pacific Northwest National Laboratory and University of Houston, respectively. The image depicts bulk sorbents that can be used for separations, a microscopic image of a zeolite crystal framework, and an individual pore operating as a size-exclusion sieve. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

New approaches to tailor the synthesis of zeolite polymorphs can lead to breakthroughs in applications spanning from separations to adsorption. A comparison of small ‐ pore zeolite GIS polymorphs P1 and P2 revealed marked differences in their thermal stability. Moreover, adsorption experiments and DFT studies collectively showed that GIS polymorphs are promising materials for selective separation of small molecules. More information can be found in the Full Paper by R. K. Motkuri, J. D. Rimer et al. on page 16078 ff. [ABSTRACT FROM AUTHOR]