A Universal Standard Archive File for Adsorption Data

Three-dimensional van der Waals open frameworks

Open-framework materials are constructed by connecting molecular components via strong bonds. It is generally believed that non-covalent interactions are too weak to hold the building blocks and generate stable open voids. Here we show that van der Waals interactions enable the construction of robust three-dimensional frameworks, referred to as van der Waals open frameworks (WaaFs). The key to successful synthesis of WaaFs is the use of octahedral metal-organic polyhedra with size larger than 2 nm as building blocks and their packing into a sparse diamond network with large extrinsic porosity. The well-defined faces composed of multiple planar moieties increase the intermolecular contact area to achieve an interaction energy above 400 kJ mol-1. We show that the WaaFs exhibit high thermal stability and high specific surface area as well as framework assembly with a reversible nature.

The role of surface deformation on responsivity of the pillared layer metal-organic framework DUT-8(Ni)

A unique feature of flexible metal-organic frameworks (MOFs) is their ability to respond dynamically towards molecular stimuli by structural transitions, resulting in pore-opening and closing processes. One of the most intriguing modes is the "gating", where the material transforms from the dense to the porous state. The conditions required for the solid phase structural transition are controlled by the kinetic barriers, including nucleation of the new phase commencing on the crystallite's outer surface. Thus, surface deformation may influence the nucleation, enabling deliberate tailoring of the responsivity. In the present contribution, we investigate how chemical surface treatments (surface deformation) affect the gate opening characteristics of a typical representative of gate pressure MOFs, DUT-8(Ni) ([Ni2(ndc)2(dabco)] n , ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane). A combination of various complementary advanced characterization techniques, such as NMR, nanoFTIR, terahertz, in situ XPS, in situ EPR spectroscopies, and inverse gas chromatography, are applied to unravel the changes in surface energy and mechanism of surface deformation.

Polytriphenylamine Conjugated Microporous Polymers as Versatile Platforms for Tunable Hydrogen Storage

Hydrogen (H2) as a fuel source presents a promising route toward decarbonization, though challenges in its storage remain significant. This study explores the synthesis and characterization of polytriphenylamine (PTPA) conjugated microporous polymers (CMPs) for H2 storage. Utilizing a combination of Buchwald-Hartwig (BH) coupling, the Bristol-Xi'an Jiaotong (BXJ) approach, and variations in monomer reactive site stoichiometry, a polymer with specific surface areas in excess of 1150 m2 g-1 and micropore volume of 0.47 cm3 g-1 is developed. H2 storage capacities are measured, achieving excess gravimetric uptakes of 1.65 wt.% at 1 bar and 2.51 wt.% at 50 bar and 77 K, with total capacities reaching 4.40 wt.% at 100 bar and 77 K. Net adsorption isotherms reveal advantages to H2 storage using PTPA adsorbents over traditional compression up to pressures of 10 bar at 77 K. High mass transfer coefficients of 4.95 min-1 indicate a strong material affinity for H2. This study highlights the impact of monomer ratio adjustments on the porosity and excess, total, and net H2 adsorption capacities of PTPA-based CMPs, offering insights into the importance of a non-stoichiometric monomer concentration when developing efficient CMP-based H2 storage materials.

Engineering Photoswitching Dynamics in 3D Photochromic Metal-Organic Frameworks through a Metal-Organic Polyhedron Design

Metal-organic polyhedra (MOPs) are versatile supramolecular building blocks for the design of highly porous frameworks by reticular assembly because of their diverse geometries, multiple degrees of freedom regarding functionalization, and accessible metal sites. Lipophilic functionalization is demonstrated to enable the rational assembly and crystallization with photoactive N-donor ligands in an aliphatic solvent to achieve multiaxially aligned photoresponsive diarylethene (DTE) moieties in 3D frameworks (DUT-210(M), M = Cu and Rh) featuring cooperative switchability. Combined experimental and theoretical investigations based on in situ PXRD, UV-vis spectroscopy, and density functional theory calculations demonstrate deliberate kinetic engineering of photoswitchability based on variations in metal-ligand bond strengths. The novel porous frameworks are an important step toward the knowledge-based development of photon-driven motors, actuators, and release systems.

CO2 and Temperature Induced Switching of a Flexible Metal-Organic Framework with Surface-Mounted Nanoparticles

Within the material family of metal-organic frameworks (MOFs) the subclass of flexible MOFs (flexMOFs) has attracted great attention, showing structural flexibility as a response to external stimuli such as guest adsorption, temperature, and pressure. Hybrid composites like nanoparticle (NP) loaded flexible MOFs, which stand to potentially combine advantageous properties of both are yet largely unexplored. Here the synthesis of flexMOFs with surface mounted nanoparticles, e. g. NP@Zn2(BME-bdc)2dabco composites (NP = Pt and SiO2 nanoparticles, BME-bdc2- = 2,5-bismethoxyethoxy-1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) is reported, studying the impact of nanoparticles on the stimulus-responsiveness of a flexMOF. It is shown that CO2 physisorption triggered flexibility of the MOF is retained and reversible for all NP@flexMOF composites. Additionally, it is observed that NPs stabilize the large pore state of the MOF, slightly increasing and shifting the switching pressure window. This effect is also observed during temperature-induced switching but Pt@flexMOF composites partially lose long-range order during the reversion to their narrow pore state, while attached SiO2 NPs allow for a fully reversible transition. These findings suggest that the total exerted material strain triggering the switching is heavily dependent on NP size and the applied stimulus and that guest-induced switchability can be fully realized in NP@flexMOF hybrid materials.

Adsorption and Separation by Flexible MOFs

Flexible metal-organic frameworks (MOFs) offer unique opportunities due to their dynamic structural adaptability. This review explores the impact of flexibility on gas adsorption, highlighting key concepts for gas storage and separation. Specific examples demonstrate the principal effectiveness of flexible frameworks in enhancing gas uptake and working capacity. Additionally, mixed gas adsorption and separation of mixtures are reviewed, showcasing their potential in selective gas separation. The review also discusses the critical role of the single gas isotherms analysis and adsorption conditions in designing separation experiments. Advanced combined characterization techniques are crucial for understanding the behavior of flexible MOFs, including monitoring of phase transitions, framework-guest and guest-guest interactions. Key challenges in the practical application of flexible adsorbents are addressed, such as the kinetics of switching, volume change, and potential crystal damage during phase transitions. Furthermore, the effects of additives and shaping on flexibility and the "slipping off effect" are discussed. Finally, the benefits of phase transitions beyond improved working capacity and selectivity are outlined, with a particular focus on the advantages of intrinsic thermal management. This review highlights the potential and challenges of using flexible MOFs in gas storage and separation technologies, offering insights for future research and application.

Dynamic two-dimensional covalent organic frameworks

Porous covalent organic frameworks (COFs) enable the realization of functional materials with molecular precision. Past research has typically focused on generating rigid frameworks where structural and optoelectronic properties are static. Here we report dynamic two-dimensional (2D) COFs that can open and close their pores upon uptake or removal of guests while retaining their crystalline long-range order. Constructing dynamic, yet crystalline and robust frameworks requires a well-controlled degree of flexibility. We have achieved this through a 'wine rack' design where rigid π-stacked columns of perylene diimides are interconnected by non-stacked, flexible bridges. The resulting COFs show stepwise phase transformations between their respective contracted-pore and open-pore conformations with up to 40% increase in unit-cell volume. This variable geometry provides a handle for introducing stimuli-responsive optoelectronic properties. We illustrate this by demonstrating switchable optical absorption and emission characteristics, which approximate 'null-aggregates' with monomer-like behaviour in the contracted COFs. This work provides a design strategy for dynamic 2D COFs that are potentially useful for realizing stimuli-responsive materials.

Computational Simulations of Metal-Organic Frameworks to Enhance Adsorption Applications

Metal-organic frameworks (MOFs), renowned for their exceptional porosity and crystalline structure, stand at the forefront of gas adsorption and separation applications. Shortly after their discovery through experimental synthesis, computational simulations quickly become an important method in broadening the use of MOFs by offering deep insights into their structural, functional, and performance properties. This review specifically addresses the pivotal role of molecular simulations in enlarging the molecular understanding of MOFs and enhancing their applications, particularly for gas adsorption. After reviewing the historical development and implementation of molecular simulation methods in the field of MOFs, high-throughput computational screening (HTCS) studies used to unlock the potential of MOFs in CO2 capture, CH4 storage, H2 storage, and water harvesting are visited and recent advancements in these adsorption applications are highlighted. The transformative impact of integrating artificial intelligence with HTCS on the prediction of MOFs' performance and directing the experimental efforts on promising materials is addressed. An outlook on current opportunities and challenges in the field to accelerate the adsorption applications of MOFs is finally provided.

Guest-selective shape-memory effect in a switchable metal-organic framework DUT-8(Zn)

Crystal size engineering allows tailoring of flexible metal-organic frameworks (MOFs) to achieve new properties. The gating type flexibility of the DUT-8(Zn) ([Zn2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane) compound is known to be extremely particle size sensitive. Here, the physisorption of ethanol vapor gives rise to so-called shape-memory effect, leading to rigidification and flexibility suppression. According to powder X-ray diffraction and nitrogen physisorption experiments, the open pore phase is retained selectively after desorption of alcohols, which could be attributed to the nano-structuring and surface deformation of the crystals as a result of exposure to alcohols.

Physicochemical Properties, Equilibrium Adsorption Performance, Manufacturability, and Stability of TIFSIX-3-Ni for Direct Air Capture of CO2

The use of adsorbents for direct air capture (DAC) of CO2 is regarded as a promising and essential carbon dioxide removal technology to help meet the goals outlined by the 2015 Paris Agreement. A class of adsorbents that has gained significant attention for this application is ultramicroporous metal organic frameworks (MOFs). However, the necessary data needed to facilitate process scale evaluation of these materials is not currently available. Here, we investigate TIFSIX-3-Ni, a previously reported ultramicroporous MOF for DAC, and measure several physicochemical and equilibrium adsorption properties. We report its crystal structure, textural properties, thermal stability, specific heat capacity, CO2, N2, and H2O equilibrium adsorption isotherms at multiple temperatures, and Ar and O2 isotherms at a single temperature. For CO2, N2, and H2O, we also report isotherm model fitting parameters and calculate heats of adsorption. We assess the manufacturability and process stability of TIFSIX-3-Ni by investigating the impact of batch reproducibility, binderless pelletization, humidity, and adsorption-desorption cycling (50 cycles) on its crystal structure, textural properties, and CO2 adsorption. For pelletized TIFSIX-3-Ni, we also report its skeletal, pellet, and bed density, total pore volume, and pellet porosity. Overall, our data enable initial process modeling and optimization studies to evaluate TIFSIX-3-Ni for DAC at the process scale. They also highlight the possibility to pelletize TIFSIX-3-Ni and the limited stability of the MOF under humid and oxidative conditions as well as upon multiple adsorption-desorption cycles.

Describing and Sharing Molecular Visualizations Using the MolViewSpec Toolkit

With the ever-expanding toolkit of molecular viewers, the ability to visualize macromolecular structures has never been more accessible. Yet, the idiosyncratic technical intricacies across tools and the integration complexities associated with handling structure annotation data present significant barriers to seamless interoperability and steep learning curves for many users. The necessity for reproducible data visualizations is at the forefront of the current challenges. Recently, we introduced MolViewSpec (homepage: https://molstar.org/mol-view-spec/, GitHub project: https://github.com/molstar/mol-view-spec), a specification approach that defines molecular visualizations, decoupling them from the varying implementation details of different molecular viewers. Through the protocols presented herein, we demonstrate how to use MolViewSpec and its 3D view-building Python library for creating sophisticated, customized 3D views covering all standard molecular visualizations. MolViewSpec supports representations like cartoon and ball-and-stick with coloring, labeling, and applying complex transformations such as superposition to any macromolecular structure file in mmCIF, BinaryCIF, and PDB formats. These examples showcase progress towards reusability and interoperability of molecular 3D visualization in an era when handling molecular structures at scale is a timely and pressing matter in structural bioinformatics as well as research and education across the life sciences. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Creating a MolViewSpec view using the MolViewSpec Python package Basic Protocol 2: Creating a MolViewSpec view with reference to MolViewSpec annotation files Basic Protocol 3: Creating a MolViewSpec view with labels and other advanced features Support Protocol 1: Computing rotation and translation vectors Support Protocol 2: Creating a MolViewSpec annotation file.

Quantifying the Uncertainty of Force Field Selection on Adsorption Predictions in MOFs

Comparisons between simulated and experimental adsorption isotherms in MOFs are fraught with challenges. On the experimental side, there is significant variation between isotherms measured on the same system, with a significant percentage (∼20%) of published data being considered outliers. On the simulation side, force fields are often chosen "off-the-shelf" with little or no validation. The effect of this choice on the reliability of simulated adsorption predictions has not yet been rigorously quantified. In this work, we fill this gap by systematically quantifying the uncertainty arising from force field selection on adsorption isotherm predictions. We choose methane adsorption, where electrostatic interactions are negligible, to independently study the effect of the framework Lennard-Jones parameters on a series of prototypical materials that represent the most widely studied MOF "families". Using this information, we compute an adsorption "consensus isotherm" from simulations, including a quantification of uncertainty, and compare it against a manually curated set of experimental data from the literature. By considering many experimental isotherms measured by different groups and eliminating outliers in the data using statistical analysis, we conduct a rigorous comparison that avoids the pitfalls of the standard approach of comparing simulation predictions to a single experimental data set. Our results show that (1) the uncertainty in simulated isotherms can be as large as 15% and (2) standard force fields can provide reliable predictions for some systems but can fail dramatically for others, highlighting systematic shortcomings in those models. Based on this, we offer recommendations for future simulation studies of adsorption, including high-throughput computational screening of MOFs.

Multiscale Modeling of Physical Properties of Nanoporous Frameworks: Predicting Mechanical, Thermal, and Adsorption Behavior

ConspectusNanoporous frameworks are a large and diverse family of supramolecular materials, whose chemical building units (organic, inorganic, or both) are assembled into a 3D architecture with well-defined connectivity and topology, featuring intrinsic porosity. These materials play a key role in various industrial processes and applications, such as energy production and conversion, fluid separation, gas storage, water harvesting, and many more. The performance and suitability of nanoporous materials for each specific application are directly related to both their physical and chemical properties, and their determination is crucial for process engineering and optimization of performances. In this Account, we focus on some recent developments in the multiscale modeling of physical properties of nanoporous frameworks, highlighting the latest advances in three specific areas: mechanical properties, thermal properties, and adsorption.In the study of the mechanical behavior of nanoporous materials, the past few years have seen a rapid acceleration of research. For example, computational resources have been pooled to create a public large-scale database of elastic constants as part of the Materials Project initiative to accelerate innovation in materials research: those can serve as a basis for data-based discovery of materials with targeted properties, as well as the training of machine learning predictor models.The large-scale prediction of thermal behavior, in comparison, is not yet routinely performed at such a large scale. Tentative databases have been assembled at the DFT level on specific families of materials, such as zeolites, but prediction at larger scale currently requires the use of transferable classical force fields, whose accuracy can be limited.Finally, adsorption is naturally one of the most studied physical properties of nanoporous frameworks, as fluid separation or storage is often the primary target for these materials. We highlight the recent achievements and open challenges for adsorption prediction at a large scale, focusing in particular on the accuracy of computational models and the reliability of comparisons with experimental data available. We detail some recent methodological improvements in the prediction of adsorption-related properties: in particular, we describe the recent research efforts to go beyond the study of thermodynamic quantities (uptake, adsorption enthalpy, and thermodynamic selectivity) and predict transport properties using data-based methods and high-throughput computational schemes. Finally, we stress the importance of data-based methods of addressing all sources of uncertainty.The Account concludes with some perspectives about the latest developments and open questions in data-based approaches and the integration of computational and experimental data together in the materials discovery loop.

Chemoselectivity Inversion of Responsive Metal-Organic Frameworks by Particle Size Tuning in the Micrometer Regime

Gated adsorption is one of the unique physical properties of flexible metal-organic frameworks with high application potential in selective adsorption and sensing of molecules. Despite recent studies that have provided some guidelines in understanding and designing structural flexibility for controlling gate opening by chemical modification of the secondary building units, currently, there is no established strategy to design a flexible MOF showing selective gated adsorption for a specific guest molecule. In a present contribution it is demonstrated for the first time, that the selectivity in the gate opening of a particular compound can be tuned, changed, and even reversed using particle size engineering DUT-8(Zn) ([Zn2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) experiences phase transition from open (op) to closed (cp) pore phase upon removal of solvent from the pores. Microcrystals show selective reopening in the presence of dichloromethane (DCM) over alcohols. Crystal downsizing to micron size unexpectedly reverses the gate opening selectivity, causing DUT-8(Zn) to open its nanosized pores for alcohols but suppressing the responsivity toward DCM.

Efficient Modeling of Water Adsorption in MOFs Using Interpolated Transition Matrix Monte Carlo

With the specter of accelerating climate change, securing access to potable water has become a critical global challenge. Atmospheric water harvesting (AWH) through metal-organic frameworks (MOFs) emerges as one of the promising solutions. The standard numerical methods applied for rapid and efficient screening for optimal sorbents face significant limitations in the case of water adsorption (slow convergence and inability to overcome high energy barriers). To address these challenges, we employed grand canonical transition matrix Monte Carlo (GC-TMMC) methodology and proposed an efficient interpolation scheme that significantly reduces the number of required simulations while maintaining accuracy of the results. Through the example of water adsorption in three MOFs: MOF-303, MOF-LA2-1, and NU-1000, we show that the extrapolation of the free energy landscape allows for prediction of the adsorption properties over a continuous range of pressure and temperature. This innovative and versatile method provides rich thermodynamic information, enabling rapid, large-scale computational screening of sorbents for adsorption, applicable for a variety of sorbents and gases. As the presented methodology holds strong applicative potential, we provide alongside this paper a modified version of the RASPA2 code with a ghost swap move implementation and a Python library designed to minimize the user's input for analyzing data derived from the TMMC simulations.

Measurement of Physicochemical Properties and CO2, N2, Ar, O2, and H2O Unary Adsorption Isotherms of Purolite A110 and Lewatit VP OC 1065 for Application in Direct Air Capture

Direct air capture (DAC) using solid adsorbents has gained significant attention as a carbon dioxide removal (CDR) technology to help limit global temperature rise to below 2 °C. One large area of focus is the development of new adsorbent materials for DAC. However, the necessary data needed to employ these materials in process models for adsorbent screening are rarely available. Here, we showcase Purolite A110, a commercially available amine-functionalized polymeric resin, as a new candidate adsorbent for DAC and compare its properties to a current benchmark, Lewatit VP OC 1065. For both materials, we report their chemical features and composition, skeletal, particle, and bed density, total pore volume, particle porosity, BET area, thermal stability, and specific heat capacity. We determine their equilibrium sorption properties by measuring the volumetric CO2 isotherms at 288, 298, 308, 333, 343, 353, and 393 K, N2 and H2O isotherms at 288, 298, and 308 K, and Ar and O2 isotherms at 298 K. For CO2, N2, and H2O, we also present the corresponding isotherm model fitting parameters and heats of adsorption. These data can help facilitate process modeling and optimization studies to properly assess these adsorbents at scale.

Leveraging Machine Learning for Metal-Organic Frameworks: A Perspective

Metal-organic frameworks (MOFs) have attracted tremendous interest because of their tunable structures, functionalities, and physiochemical properties. The nearly infinite combinations of metal nodes and organic linkers have led to the synthesis of over 100,000 experimental MOFs and the construction of millions of hypothetical counterparts. It is intractable to identify the best candidates in the immense chemical space of MOFs for applications via conventional trial-to-error experiments or brute-force simulations. Over the past several years, machine learning (ML) has substantially transformed the way of MOF discovery, design, and synthesis. Driven by the abundant data from experiments or simulations, ML can not only efficiently and accurately predict MOF properties but also quantitatively derive structure-property relationships for rational design and screening. In this Perspective, we summarize recent achievements in leveraging ML for MOFs from the aspects of data acquisition, featurization, model training, and applications. Then, current challenges and new opportunities are discussed for the future exploration of ML to accelerate the development of new MOFs in this vibrant field.

Integration of Triphenylene-Based Conductive Metal-Organic Frameworks into Carbon Nanotube Electrodes for Boosting Nonenzymatic Glucose Sensing

The rational design and preparation of conductive metal-organic frameworks (MOFs) are alluring and challenging pathways to develop active catalysts toward electrocatalytic glucose oxidation. The hybridization of conductive MOFs with carbon nanotubes (CNTs) in the form of a composite can greatly improve the electrocatalytic performance. Herein, a facile one-step synthetic strategy is utilized to fabricate a Ni3(HHTP)2/CNT (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) composite for nonenzymatic detection of glucose in an alkaline solution. The Ni3(HHTP)2/CNT composite, as an electrochemical glucose sensor material, exhibits superior electrocatalytic activity toward glucose oxidation with a wide detection range of up to 3.9 mM, a low detection limit of 4.1 μM (signal/noise = 3), a fast amperometric response time of <2 s, and a high sensitivity of 4774 μA mM-1 cm-2, surpassing the performance of some recently reported nonenzymatic transition-metal-based glucose sensors. In addition, the composite sensor also shows outstanding selectivity, robust long-term electrochemical stability, favorable anti-interference properties, and good reproducibility. This work displays the effectiveness of enhancing the electrocatalytic performance toward glucose detection by combing conductive MOFs with CNTs, thereby opening up an applicable and encouraging approach for the design of advanced nonenzymatic glucose sensors.

An Upper Bound Visualization of Design Trade-Offs in Adsorbent Materials for Gas Separations: CO2 , N2 , CH4 , H2 , O2 , Xe, Kr, and Ar Adsorbents

The last 20 years have seen many publications investigating porous solids for gas adsorption and separation. The abundance of adsorbent materials (this work identifies 1608 materials for CO2 /N2 separation alone) provides a challenge to obtaining a comprehensive view of the field, identifying leading design strategies, and selecting materials for process modeling. In 2021, the empirical bound visualization technique was applied, analogous to the Robeson upper bound from membrane science, to alkane/alkene adsorbents. These bound visualizations reveal that adsorbent materials are limited by design trade-offs between capacity, selectivity, and heat of adsorption. The current work applies the bound visualization to adsorbents for a wider range of gas pairs, including CO2 , N2 , CH4 , H2 , Xe, O2 , and Kr. How this visual tool can identify leading materials and place new material discoveries in the context of the wider field is presented. The most promising current strategies for breaking design trade-offs are discussed, along with reproducibility of published adsorption literature, and the limitations of bound visualizations. It is hoped that this work inspires new materials that push the bounds of traditional trade-offs while also considering practical aspects critical to the use of materials on an industrial scale such as cost, stability, and sustainability.

Particle size-dependent flexibility in DUT-8(Cu) pillared layer metal-organic framework

The nature of metal in the isomorphous flexible metal-organic frameworks is often reported to influence flexibility and responsivity. A prominent example of such behaviour is the DUT-8(M) family ([M₂(2,6-ndc)₂(dabco)]_n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), where the isostructural compounds with Ni, Zn, Co, and Cu in the paddle wheel cluster are known. The macro-sized crystals of Ni, Co, and Zn based compounds transform to the closed pore (cp) phase under desolvation and show typical gate opening behaviour upon adsorption. The choice of metal, in this case, allows the adjustment of switching kinetics, selectivity in adsorption, and gate-opening pressures. The submicron-sized crystals of of Ni, Co, and Zn based compounds remain in the open pore (op) phase after desolvation. In this contribution, we demonstrate that the presence of Cu in the paddle wheel leads to fundamentally different flexible behaviour. The DUT-8(Cu) desolvation does not lead to the formation of the cp phase, independent of the particle size regime. However, according to in situ powder diffraction analysis, the desolvated, macro-sized crystals of DUT-8(Cu)_op show breathing upon adsorption of CO₂ at 195 K. The submicron-sized particles show rigid, nonresponsive behaviour.

Reduced thermal expansion by surface-mounted nanoparticles in a pillared-layered metal-organic framework

Control of thermal expansion (TE) is important to improve material longevity in applications with repeated temperature changes or fluctuations. The TE behavior of metal-organic frameworks (MOFs) is increasingly well understood, while the impact of surface-mounted nanoparticles (NPs) on the TE properties of MOFs remains unexplored despite large promises of NP@MOF composites in catalysis and adsorbate diffusion control. Here we study the influence of surface-mounted platinum nanoparticles on the TE properties of Pt@MOF (Pt@Zn₂(DP-bdc)₂dabco; DP-bdc^2-=2,5-dipropoxy-1,4-benzenedicarboxylate, dabco=1,4-diazabicyclo[2.2.2]octane). We show that TE is largely retained at low platinum loadings, while high loading results in significantly reduced TE at higher temperatures compared to the pure MOF. These findings support the chemical intuition that surface-mounted particles restrict deformation of the MOF support and suggest that composite materials exhibit superior TE properties thereby excluding thermal stress as limiting factor for their potential application in temperature swing processes or catalysis.

The Dilemma of Reproducibility of Gating Isotherms for Flexible MOFs

Porous materials receive a high level of scientific and technological interest due to their applications in various fields such as adsorption, separation and storage, catalysis, ion exchange, nanotechnology, etc. Gas adsorption is a well-established tool for the characterization of the texture of porous solids. Physisorption isotherms are generally expected to be well reproducible for rigid adsorbents, but this is not always the case for nonrigid (flexible) materials. The presence of a metastability region and sensitivity of the activation barriers to the material's texture often influence the isotherms' run. Here, we address the complexity that arises in terms of reproducibility and sample handling for flexible metal-organic frameworks, with the example of DUT-8(Ni). It belongs to the group of "gate opening" metal-organic frameworks and is a typical representative of the pillared layer compounds. We propose characteristic parameters for the analysis and comparison of adsorption isotherms, showing the "gate opening" step, associated with the adsorption-induced solid-state phase transition. A set of 50 nitrogen physisorption isotherms measured at 77 K were analyzed and correlated with the synthetic and outgassing conditions. The study highlights the importance of accurate descriptions and record-keeping of experimental details and their role in the replication of scientific results.

Into the Unknown: How Computation Can Help Explore Uncharted Material Space

Novel functional materials are urgently needed to help combat the major global challenges facing humanity, such as climate change and resource scarcity. Yet, the traditional experimental materials discovery process is slow and the material space at our disposal is too vast to effectively explore using intuition-guided experimentation alone. Most experimental materials discovery programs necessarily focus on exploring the local space of known materials, so we are not fully exploiting the enormous potential material space, where more novel materials with unique properties may exist. Computation, facilitated by improvements in open-source software and databases, as well as computer hardware has the potential to significantly accelerate the rational development of materials, but all too often is only used to postrationalize experimental observations. Thus, the true predictive power of computation, where theory leads experimentation, is not fully utilized. Here, we discuss the challenges to successful implementation of computation-driven materials discovery workflows, and then focus on the progress of the field, with a particular emphasis on the challenges to reaching novel materials.

Tunable Confined Aliphatic Pore Environment in Robust Metal-Organic Frameworks for Efficient Separation of Gases with a Similar Structure

The fine-tuning of the pore structure of metal-organic frameworks (MOFs) is of critical importance to developing energy-efficient processes for the challenging separation of structurally similar molecules. Herein, we demonstrate a strategy to realize a quasi-three-dimensional refinement of the pore structure that utilizes the tunability of ring size and number in polycycloalkane-dicarboxylate ligands. Two hydrolytically stable MOFs with a confined aliphatic pore environment, ZUL-C1 and ZUL-C2, were, for the first time, synthesized and applied in separating low-concentration C2-C3 hydrocarbons from natural gas and ultralow-concentration Xe from used nuclear fuel (UNF) off-gas. Validated by X-ray diffraction and modeling, an expansion of the polycycloalkane moiety enables sub-angstrom contraction in specific directions and forms a pore surface with more alkyl sites, which affords stronger trapping of guest molecules with relatively higher polarizability. The resultant material exhibits record C₂H₆/CH₄ and C₃H₈/CH₄ selectivities coupled with a benchmark low-pressure C₂H₆ capacity in alkane mixture separation and also a benchmark Xe capacity at extremely diluted feed concentration and record Kr productivity for the Xe/Kr (20:80, v/v) mixture in Xe/Kr separation.

Making the collective knowledge of chemistry open and machine actionable

Large amounts of data are generated in chemistry labs-nearly all instruments record data in a digital form, yet a considerable proportion is also captured non-digitally and reported in ways non-accessible to both humans and their computational agents. Chemical research is still largely centred around paper-based lab notebooks, and the publication of data is often more an afterthought than an integral part of the process. Here we argue that a modular open-science platform for chemistry would be beneficial not only for data-mining studies but also, well beyond that, for the entire chemistry community. Much progress has been made over the past few years in developing technologies such as electronic lab notebooks that aim to address data-management concerns. This will help make chemical data reusable, however it is only one step. We highlight the importance of centring open-science initiatives around open, machine-actionable data and emphasize that most of the required technologies already exist-we only need to connect, polish and embrace them.

Improving Reproducibility in Hydrogen Storage Material Research

Research into new reversible hydrogen storage materials has the potential to help accelerate the transition to a hydrogen economy. The discovery of an efficient and cost-effective method of safely storing hydrogen would revolutionise its use as a sustainable energy carrier. Accurately measuring storage capacities - particularly of novel nanomaterials - has however proved challenging, and progress is being hindered by ongoing problems with reproducibility. Various metal and complex hydrides are being investigated, together with nanoporous adsorbents such as carbons, metal-organic frameworks and microporous organic polymers. The hydrogen storage properties of these materials are commonly determined using either the manometric (or Sieverts) technique or gravimetric methods, but both approaches are prone to significant error, if not performed with great care. Although commercial manometric and gravimetric instruments are widely available, they must be operated with an awareness of the limits of their applicability and the error sources inherent to the measurement techniques. This article therefore describes the measurement of hydrogen sorption and covers the required experimental procedures, aspects of troubleshooting and recommended reporting guidelines, with a view of helping improve reproducibility in experimental hydrogen storage material research.

Alkyl decorated metal-organic frameworks for selective trapping of ethane from ethylene above ambient pressures

The trapping of paraffins is beneficial compared to selective olefin adsorption for adsorptive olefin purification from a process engineering point of view. Here we demonstrate the use of a series of Zn2(X-bdc)2(dabco) (where X-bdc2- is bdc2- = 1,4-benzenedicarboxylate with substituting groups X, DM-bdc2- = 2,5-dimethyl-1,4-benzenedicarboxylate or TM-bdc2- = 2,3,5,6-tetramethyl-1,4-benzenedicarboxylate and dabco = diazabicyclo[2.2.2.]octane) metal-organic frameworks (MOFs) for the adsorptive removal of ethane from ethylene streams. The best performing material from this series is Zn2(TM-bdc)2(dabco) (DMOF-TM), which shows a high ethane uptake of 5.31 mmol g-1 at 110 kPa, with a good IAST selectivity of 1.88 towards ethane over ethylene. Through breakthrough measurements a high productivity of 13.1 L kg-1 per breakthrough is revealed with good reproducibility over five consecutive cycles. Molecular simulations show that the methyl groups of DMOF-TM are forming a van der Waals trap with the methylene groups from dabco, snuggly fitting the ethane. Further, rarely used high pressure coadsorption measurements, in pressure regimes that most scientific studies on hydrocarbon separation on MOFs ignore, reveal an increase in ethane capacity and selectivity for binary mixtures with increased pressures. The coadsorption measurements reveal good selectivity of 1.96 at 1000 kPa, which is verified also through IAST calculations up to 3000 kPa. This study overall showcases the opportunities that pore engineering by alkyl group incorporation and pressure increase offer to improve hydrocarbon separation in reticular materials.