Size-dependent guest-memory switching of the flexible and robust adsorption characteristics of layered metal-organic frameworks.

Flexible-robust metal-organic frameworks (MOFs), which exhibit unique hybrid nature comprising both flexible and rigid framework characteristics, exhibit high potential for hydrocarbon separations. However, no clear guidelines have been established to regulate their hybrid characteristics owing to limited understanding of their adsorption mechanism. This study investigates the effects of the particle size of a flexible-robust MOF on its adsorption and structural transition behaviors.

Modeling order-disorder boundaries of colloidal dispersions in organic solvents using interaction force measurements.

Hypothesis: The formation of soft colloidal crystals, which are nonclose-packed ordered arrays of colloidal particles suspended in a solvent, is dictated by a single physical factor that yields a fixed threshold at order-disorder boundaries for different experimental conditions such as ion concentration, solvent type, and particle size. Identifying the determinant factor and its threshold value should enable the prediction of the critical concentrations of colloidal particles to form soft colloidal crystals.

Experiments: Soft colloidal crystals were fabricated using a series of monohydric alcohols as dispersion media and reflectance spectra were measured to locate order-disorder boundaries.

Solute interaction-driven and solvent interaction-driven liquid-liquid phase separation induced by molecular size difference.

We conducted molecular dynamics (MD) simulations in a binary Lennard-Jones system as a model system for molecular solutions and investigated the mechanism of liquid-liquid phase separation (LLPS), which has recently been recognized as a fundamental step in crystallization and organelle formation. Our simulation results showed that LLPS behavior varied drastically with the size ratio of solute to solvent molecules. Interestingly, increasing the size ratio can either facilitate or inhibit LLPS, depending on the combination of interaction strengths.

Generalised analytical method unravels framework-dependent kinetics of adsorption-induced structural transition in flexible metal-organic frameworks.

Flexible metal-organic frameworks (MOFs) exhibiting adsorption-induced structural transition can revolutionise adsorption separation processes, including CO separation, which has become increasingly important in recent years. However, the kinetics of this structural transition remains poorly understood despite being crucial to process design. Here, the CO-induced gate opening of ELM-11 ([Cu(BF)(4,4'-bipyridine)]) is investigated by time-resolved in situ X-ray powder diffraction, and a theoretical kinetic model of this process is developed to gain atomistic insight into the transition dynamics.

Fast Gas-Adsorption Kinetics in Supraparticle-Based MOF Packings with Hierarchical Porosity.

Metal-organic frameworks (MOFs) are microporous adsorbents for high-throughput gas separation. Such materials exhibit distinct adsorption characteristics owing to the flexibility of the crystal framework in a nanoparticle, which can be different from its bulk crystal. However, for practical applications, such particles need to be compacted into macroscopic pellets, creating mass-transport limitations.

Crossover Sorption of C H /CO and C H /C H in Soft Porous Coordination Networks.

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of "crossover sorption," in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures.

Theoretical isotherm equation for adsorption-induced structural transition on flexible metal-organic frameworks.

Flexible metal-organic frameworks (MOFs) exhibit an adsorption-induced structural transition known as "gate opening" or "breathing," resulting in an S-shaped adsorption isotherm. This unique feature of flexible MOFs offers significant advantages, such as a large working capacity, high selectivity, and intrinsic thermal management capability, positioning them as crucial candidates for revolutionizing adsorption separation processes. Therefore, the interest in the industrial applications of flexible MOFs is increasing, and the adsorption engineering for flexible MOFs is becoming important.

Validating the Mechanism Underlying the Slacking of the Gate-Opening Behavior in Flexible Metal-Organic Frameworks Arising from the Application of External Force.

Flexible metal-organic frameworks (MOFs) are innovative adsorbents expected to revolutionize conventional separation systems as they exhibit stepwise adsorption arising from structural transitions, commonly known as "gate opening." However, because MOFs are typically obtained in powder form, they require shaping for industrial applications. In our previous study, we reported that the stepwise uptake observed in the CO gate opening of ELM-11 ([Cu(BF)(4,4-bipyridine)]) became less distinct when molded with polymer binders and found that this slacking phenomenon could be caused by the polymer binder inhibiting the structural change of the ELM-11 particles.

Mechanism of Nucleation Pathway Selection in Binary Lennard-Jones Solution: A Combined Study of Molecular Dynamics Simulation and Free Energy Analysis.

The nucleation process, which is the initial step in particle synthesis, determines the properties of the resultant particles. Although recent studies have observed various nucleation pathways, the physical factors that determine these pathways have not been fully elucidated. Herein, we conducted molecular dynamics simulations in a binary Lennard-Jones system as a model solution and found that the nucleation pathway can be classified into four types depending on microscopic interactions.

High-Performance Carbon Molecular Sieves for the Separation of Propylene and Propane.

High-performance carbon molecular sieves (CMSs) for the separation of propylene (CH) and propane (CH) were synthesized in this study by chemical vapor deposition (CVD) of benzene on the pore entrances of activated carbon. The CH and CH separation characteristics of the CMSs were controlled by altering the amount of carbon deposited during CVD, and the resulting characteristic curve featuring the kinetic selectivity of CH over CH as a function of the adsorption rate constant of CH is considered to be the upper bound of the CH-CH separation factor for current CMSs because of the presence of previously reported CMS data under this curve. Additionally, CMS models were constructed using grand canonical molecular dynamics (GCMD) simulations mimicking the process of CVD, which revealed that the kinetic selectivity of CH over CH strongly depended on the size of the pore entrances at the level of 0.

Slacking of Gate Adsorption Behavior on Metal-Organic Frameworks under an External Force.

As flexible metal-organic frameworks (MOFs) and their gate adsorption behaviors are increasingly expected to be used in gas storage and separation systems, evaluating their performance by considering their usage patterns in actual processes is becoming increasingly important. Herein, we show that the shaping of the elastic layer-structured MOF-11 (ELM-11; [Cu(BF)(4,4'-bipyridine)]) into pellet forms using polymer binders smears its stepwise uptake associated with the CO gate adsorption. This is a critical problem because the superior adsorption properties of flexible MOFs are highly dependent on the sharpness of the step.

Flow Microreactor Synthesis of Zeolitic Imidazolate Framework (ZIF)@ZIF Core-Shell Metal-Organic Framework Particles and Their Adsorption Properties.

Metal-organic frameworks (MOFs) with core-shell structures enable to enhance intrinsic properties of constituent MOFs and impart additional functional activities. Although shell thickness is a key factor for regulating the properties of core-shell MOF particles, controlling it has been challenging. The widely used batch reactor synthesis cannot produce core-shell particles with uniform shell thickness because of poor reactant mixing.

High-throughput gas separation by flexible metal-organic frameworks with fast gating and thermal management capabilities.

Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. Herein, we show that ELM-11 ([Cu(BF)(4,4'-bipyridine)]), a member of flexible metal-organic frameworks (MOFs), exhibits rapid responsiveness to a gas feed and an 'intrinsic thermal management' capability originating from a structural deformation upon gas adsorption (gate-opening). These two characteristics are suitable for developing a pressure vacuum swing adsorption (PVSA) system with rapid operations.

Multiple Roles of Polyethylenimine during Synthesis of 10 nm Thick Continuous Silver Nanoshells.

Silica@silver core-shell particles (silver nanoshells) present a wide range of applications, owing to their unique optical, chemical, and surface plasmon resonance (SPR) properties. Because SPR properties are mainly determined by shell thickness, precise shell thickness control is required. However, the synthesis of continuous nanoshells less than 10 nm thickness is still a challenge.

Direct observation of the attachment behavior of hydrophobic colloidal particles onto a bubble surface.

The attachment of solid particles to the surface of immersed gas bubbles plays a fundamental role in surface science, and hence plays key roles in various engineering fields ranging from industrial separation processes to the fabrication of functional materials. However, detailed investigation from a microscopic view on how a single particle attaches to a bubble surface and how the particle properties affect the attachment behavior has been so far scarcely addressed. Here, we observed the attachment of a single particle to a bubble surface using a high-speed camera and systematically investigated the effects of the wettability and shape of particles.

On the Convective Self-Assembly of Colloidal Particles in Nanofluid Based on in Situ Measurements of Interaction Forces.

While the currently available techniques for the self-assembly of colloidal particles show great promise owing to their simplicity and high efficiency, they are plagued by the fact that they result in colloidal crystals with defects. Here, in order to overcome this problem, we propose a strategy that uses a suspension of nanoparticles (i.e.

Force-driven reversible liquid-gas phase transition mediated by elastic nanosponges.

Nano-confined spaces in nanoporous materials enable anomalous physicochemical phenomena. While most nanoporous materials including metal-organic frameworks are mechanically hard, graphene-based nanoporous materials possess significant elasticity and behave as nanosponges that enable the force-driven liquid-gas phase transition of guest molecules. In this work, we demonstrate force-driven liquid-gas phase transition mediated by nanosponges, which may be suitable in high-efficiency heat management.

Central metal dependent modulation of induced-fit gas uptake in molecular porphyrin solids.

The induced-fit accommodation of a variety of gaseous molecules including non-polar molecules has been demonstrated in porphyrin-based supramolecular architectures for the first time. Moreover, the gas uptake behaviour can be modulated by changing the central cation of porphyrin.

Intrinsic Thermal Management Capabilities of Flexible Metal-Organic Frameworks for Carbon Dioxide Separation and Capture.

We show that flexible metal-organic frameworks (MOFs) exhibiting "gate openings/closings" for CO can intrinsically suppress the exothermic heat released by adsorption and the endothermic heat gained by desorption, both of which reduce the working capacity of CO in a separation process under near-adiabatic conditions. We use the elastic layer-structured metal-organic framework-11 (ELM-11) [Cu(4,4'-bipyridine)(BF)], which exhibits a two-step gate-adsorption isotherm, as a model system for flexible MOFs, and perform free energy analyses with the aid of grand canonical Monte Carlo simulations for ELM-11 structures that were determined by the Rietveld method using in situ synchrotron X-ray powder diffraction data. We demonstrate that the thermal management capabilities of ELM-11 showing the two-step gating for CO at lower and higher pressures are nearly identical and quite effective (41% and 44% at 298 K, respectively).

Mechanism of Kinetically Controlled Capillary Condensation in Nanopores: A Combined Experimental and Monte Carlo Approach.

We find the rule of capillary condensation from the metastable state in nanoscale pores based on the transition state theory. The conventional thermodynamic theories cannot achieve it because the metastable capillary condensation inherently includes an activated process. We thus compute argon adsorption isotherms on cylindrical pore models and atomistic silica pore models mimicking the MCM-41 materials by the grand canonical Monte Carlo and the gauge cell Monte Carlo methods and evaluate the rate constant for the capillary condensation by the transition state theory.

Critical energy barrier for capillary condensation in mesopores: Hysteresis and reversibility.

Capillary condensation in the regime of developing hysteresis occurs at a vapor pressure, Pcond, that is less than that of the vapor-like spinodal. This is because the energy barrier for the vapor-liquid transition from a metastable state at Pcond becomes equal to the energy fluctuation of the system; however, a detailed mechanism of the spontaneous transition has not been acquired even through extensive experimental and simulation studies. We therefore construct accurate atomistic silica mesopore models for MCM-41 and perform molecular simulations (gauge cell Monte Carlo and grand canonical Monte Carlo) for argon adsorption on the models at subcritical temperatures.

Understanding gate adsorption behaviour of CO2 on elastic layer-structured metal-organic framework-11.

We demonstrate that CO2 gate adsorption behaviour of elastic layer-structured metal-organic framework-11 (ELM-11: [Cu(BF4)2(4,4'-bipyridine)2]), which is a family of soft porous crystals (SPCs), can be described by a thermodynamic model by free energy analysis with the aid of an adsorption experiment and a molecular simulation. The structures of ELM-11 (closed structure) at 273 K after its evacuation and CO2-encapsulated ELM-11 (open structure) at 195-298 K were determined by the Rietveld analysis using in situ synchrotron X-ray powder diffraction data. We then performed grand canonical Monte Carlo (GCMC) simulations for CO2 adsorption on the open host framework structures of ELM-11 from the Rietveld analysis.

In situ observation of meniscus shape deformation with colloidal stripe pattern formation in convective self-assembly.

Vertical convective self-assembly is capable of fabricating stripe-patterned structures of colloidal particles with well-ordered periodicity. To unveil the mechanism of the stripe pattern formation, in the present study, we focus on the meniscus shape and conduct in situ observations of shape deformation associated with particulate line evolution. The results reveal that the meniscus is elongated downward in a concave fashion toward the substrate in accordance with solvent evaporation, while the concave deformation is accelerated by solvent flow, resulting in the rupture of the liquid film at the thinnest point of the meniscus.

Dependence of adsorption-induced structural transition on framework structure of porous coordination polymers.

Porous coordination polymers (PCPs) with soft frameworks show a gate phenomenon consisting of an abrupt structural transition induced by adsorption of guest molecules. To understand the dependence of the gating behavior on the host framework structure, we conduct grand canonical Monte Carlo simulations and a free-energy analysis of a simplified model of a stacked-layer PCP. The interlayer width of the rigid layers composing the simplified model can be changed by guest adsorption and by varying the initial interlayer width h0, which is controlled by the length of pillars between the layers.

Reversible pore size control of elastic microporous material by mechanical force.

Nanoporous materials, such as zeolites, activated carbons, and metal-organic frameworks (MOFs), are peculiar platforms in which a variety of guest molecules are stored, reacted, and/or separated. The size of the nanopores is essential to realize advanced functions. In this work, we demonstrate a very simple but innovative method for the control of nanopore size, that is, reversible and continuous control by mechanical force loaded to soft nanoporous materials.