Covalent organic frameworks (COFs) with olenfin-linked backbone and covalently attached amines (e.g. COF-999) have emerged as highly tunable and efficient sorbents for the direct air capture of CO 2 . However, the rational design of next-generation COF materials is hindered by lack of molecular-level understanding of their operating principles, largely due to the intrinsic dynamics of the COF materials. Here, we utilize reactive machine-learning interatomic potentials (MLIPs) with ab initio fidelity to perform large-scale molecular dynamics simulations integrated with enhanced sampling, allowing for exhaustively mapping the free-energy surfaces of CO 2 chemisorption into COF-999. Our results reveal that under dry conditions, stable chemisorption is restricted to amines within specific cage-like local environments, while the majority of amines remain inactive due to pronounced steric hindrance or the absence of hydrogen bonding environment. In contrast, wet COF-999 expands the population of active amines via a water-induced, loosely packed amine network and more dynamic hydrogen bonding networks, which stabilize both transition states and chemisorbed *CO 2 states. This study provides the first comprehensive molecular-level mechanistic insight into CO 2 chemisorption in COFs, establishing fundamental design principles for next-generation functional materials for carbon capture.

Amine-appended porous frameworks are leading materials for direct air capture of CO 2 . Yet the molecular origins governing CO 2 uptake within their dynamic porous environments remain poorly understood, limiting the design of next-generation frameworks. We selected covalent organic framework-999 (COF-999) as exemplar for investigating CO 2 uptake behavior using large-scale molecular dynamics simulations enabled by machine-learned interatomic potentials and enhanced sampling methods. Mapping the complex free-energy surfaces reveals pocket-like amine constructs which foster CO 2 chemisorption because hydrogen bonding within such pockets lowers activation barriers. We found that the population of active amines doubles under humid conditions because water molecules expand the amine pockets and in turn increase the number of hydrogen-bonding sites. This explains the puzzling experimental observation of doubling uptake in the presence of water. Our findings allow us to propose design principles for next-generation carbon capture materials.

Separating NH3 from N2 and H2 using adsorption onto porous materials at elevated pressures and temperatures has been proposed as a promising alternative to optimize the Haber-Bosch (HB) synthesis process. However, experimental data on NH3 adsorption at high pressure are scarce and necessary to properly evaluate NH3 adsorption as a possible and viable separation option. Using commercial Na-LTA, Na-X, and Na-Y zeolites (Si/Al 1.00, 1.26, 2.79, respectively), we evaluated the NH3 equilibrium adsorption up to 15 bar and temperatures of 323, 373, 423, and 473 K. N2 adsorption isotherms were measured at 323 and 473 K. All the zeolite samples were activated at 673 K to ensure complete dehydration. At 36 bar total pressure and 473 K, ideal adsorbed solution theory (IAST) predicts selectivity for NH3 over N2 of 265, 234, and 211 for Na-LTA, Na-X, and Na-Y, respectively. Separation factors based on IAST and kinetic selectivity are estimated as 128, 39, and 46, respectively. The enhanced selectivity of Na-LTA is attributed to diffusion limitations for N2 stemming from its narrower pore size. NH3 working capacities through 5-cycle PSA tests at 473 K directly correlate with the Si/Al ratio, with Na-Y zeolite achieving the highest working capacity at 2.50 mmol cm-3. However, VSA tests with desorption via dynamic vacuum for 10 min yielded a working capacity of up to 8.83 mmol cm-3 for Na-X. Gibbs ensemble Monte Carlo simulations are carried out to investigate the adsorption of NH3, N2, and their mixture in Na-LTA. Analysis of the simulation trajectories indicates that the NH3 molecules bind strongly to the Na+ cations and displace nitrogen in mixtures.

Glycolipids are sugar-based amphiphiles that play crucial roles in many biological processes. Under thermotropic and lyotropic conditions, glycolipids self-assemble into a variety of mesophases, including cocontinuous network phases, such as the double gyroid. In this work, a two-stage molecular dynamics simulation workflow is developed to probe network formation for solvent-free amphiphiles at different temperatures. In the first stage, the structural evolution of systems initiated in lamellar and hexagonally packed cylinder arrangements is examined as an indicator of the likelihood of network formation. In the second stage, initial configurations for four network phases are obtained by applying an external guiding field to overcome any nucleation barriers, and the stability of these network phases after switching off the guiding field is investigated. A convolutional neural network is trained and applied to assign a morphology to each snapshot from the simulation. Three anomerically pure and water-free glycolipids (2-decyl-tetradecyl-d-maltoside, 2-decyl-tetradecyl-d-cellobioside, and 2-decyl-tetradecyl-d-galactoside) were examined in this study, and the predicted phase diagrams show good alignment with experimental observations from differential scanning calorimetry and temperature-dependent small-angle X-ray scattering. The workflow presents a facile approach to probe network phase stability and paves the way for the discovery of new network-forming amphiphiles.

Covalent organic frameworks (COFs), with their modular architectures and tunable functionalities, provide a versatile platform to design sorbents for the direct capture of CO2 from air. Here, we combined density functional theory, molecular dynamics, and grand canonical Monte Carlo simulations with experiment to understand structural factors for furthering COF-999-NH2's performance as the precursor to COF-999 for direct air CO2 capture. Small energy differences among laterally shifted stackings suggest intrinsic stacking heterogeneity. The simulations show pronounced layer buckling coupled to extensive amine-nitrile hydrogen bonding and persistent pore water, which initiates undesired polymerization and undermines uptake. The predicted presence of water is confirmed by subsequent experiments. These insights point to a single, actionable design rule: exclude retained water by introducing hydrophobic pore environments to maximize the CO2 capture efficiency.

High concentration water-in-salt electrolyte (WiSE) systems can expand the electrochemical stability window of water, thereby enabling the application of water-based electrolytes in Li-ion batteries. However, the solvation structure and the dynamics of the ions are not yet fully resolved, and prior molecular-mechanics-based molecular dynamics (MMMD) simulation studies present contrasting viewpoints. In the present work, we utilize first-principles molecular dynamics (FPMD) simulations to study the structure and dynamics of high-concentration (10 and 20 m) LiTFSI electrolyte solutions at 298 and 373 K. Although computationally more expensive than the MMMD simulations, the FPMD simulations, in which the forces on the nuclei are obtained from Kohn-Sham density functional theory reflecting the instantaneous arrangement of the electron density, may offer a more accurate representation of WiSE systems where polarization and charge transfer are important. The FPMD simulations demonstrate disruption of the water hydrogen bonding environment and concurrent formation of an anionic network upon increasing the LiTFSI concentration from 10 to 20 m. However, nanoscale spatial heterogeneity is not observed. Analysis of the Li+ cation dynamics obtained from both FPMD and MMMD simulations indicates that ion transport proceeds predominantly via a mixed-mode mechanism, with contributions from both vehicular motion and hopping depending on concentration and temperature.

Cationic water-soluble deep cavitands enable hierarchical assembly-based recognition, optical detection, and extraction of perfluoroalkyl substances (PFAS) in aqueous solution. Recognition of PFAS occurs at the lower rim crown of the cavitand, which triggers self-aggregation of a PFAS-cavitand complex, allowing extraction from water. In addition, when paired with an indicator dye that can be bound in the cavity of the host molecule, the PFAS-cavitand association causes a significant (>20-fold at micromolar [PFAS]) enhancement of dye fluorescence due to conformational rearrangement of the fluxional cavitand AMI, allowing optical detection of PFAS. The cavitands are water-soluble, and the detection and recognition occur in purely aqueous solution. The association is most effective for long-chain sulfonate PFAS, and as such, selective optical detection of perfluorooctanesulfonate is possible, with a LOD = 130 nM in buffered water and 530 nM in real-world samples such as polluted canal water. By pairing the AMI host with multiple dyes in an array-based format, full discrimination of five other PFAS can be achieved at micromolar concentrations via differential sensing. In addition, the aggregation process allows extraction of PFAS from solution, and a 99% reduction of PFOS concentration in water is possible with a single treatment of an equimolar concentration of AMI cavitand. The hierarchical nature of the cavitand recognition system allows both selective, sensitive optical detection and extraction of PFAS from water with a single scaffold.

We present an updated version of the Computation-Ready, Experimental (CoRE) Metal-Organic Framework (MOF) database, which includes a curated set of computation-ready MOF crystal structures designed for high-throughput computational materials discovery. Data collection and curation procedures were improved from the previous version to enable more frequent updates in the future. Machine-learning-predicted properties, such as stability metrics and heat capacities, are included in the dataset to streamline screening activities. An updated version of MOFid was developed to provide detailed information on metal nodes, organic linkers, and topologies of an MOF structure. DDEC6 partial atomic charges of MOFs were assigned based on a machine-learning model. Gibbs ensemble Monte Carlo simulations were used to classify the hydrophobicity of MOFs. The finalized dataset was subsequently used to perform integrated material-process screening for various carbon-capture conditions using high-fidelity temperature-swing adsorption (TSA) simulations. Our workflow identified multiple MOF candidates that are predicted to outperform CALF-20 for these applications.

A comprehensive set of single-component and binary isotherms were collected for ethanol/water adsorption into the siliceous forms of 185 known zeolites using grand-canonical Monte Carlo simulations. Using these data, a systematic analysis of ideal/real adsorbed-solution theory (IAST/RAST) was conducted and activity coefficients were derived for ethanol/water mixtures adsorbed in different zeolites based on RAST. It was found that activity coefficients of ethanol are close to unity while activity coefficients of water are larger in most zeolites, indicating a positive excess free energy of the mixture. This observation can be attributed to water/ethanol interactions being less favorable than water/water interactions in the single-component adsorption of water at comparable loadings. The deviation from ideal behavior can be highly structure-dependent but no clear correlation with pore diameters was identified. Our analysis also demonstrates the following: (1) accurate unary isotherms in the low-loading regime are critical for obtaining physically sensible activity coefficients; (2) the global regression scheme to solve for activity model parameters performs better than fitting activity models to activity coefficients calculated locally at each binary state point; and (3) including the dependence on adsorption potential offers only a minor benefit for describing binary adsorption at the lowest fugacities. Finally, the Margules activity model was found incapable of capturing the non-ideal adsorption behavior over the entire range of fugacities and compositions in all zeolites, but for conditions typical of solution-phase adsorption, RAST predictions using zeolite-specific or even bulk Margules parameters provide an improved description compared to IAST.

Molecular dynamics simulations are used to investigate the phase behavior of asymmetric AB1B2-type miktoarm triblock amphiphiles, composed of a sugar-based acyclic headgroup (A) and two hydrocarbon tails (B1 and B2). AB1B2 amphiphiles with significantly shorter B2 tails (f B1 /F B2 ≫ 1, where f i is the volume fraction) form lamellar (LAM) and perforated lamellae (PL) structures, whereas those with nearly equal tail lengths (f B2 ≈ F B1 ) assemble into hexagonally packed cylinders (CYL). Amphiphiles with a B1/B2 length ratio near 2:1 (2f B2 ≈ F B1 ) stabilize double gyroid (DG) networks, where the headgroups form the interconnected channels and the tails constitute the matrix, displaying feature sizes from 1.7 to 3.3 nm across a broad volume fraction range with 0.22 ≤ f A ≤ 0.40 . For potential applications in membrane separation at infinite dilution, these networks significantly hinder the diffusion of polar molecules, while nonpolar molecules diffuse relatively unimpeded. Diffusion selectivities near 3 are found for 1-butanol versus water and n-hexane versus methanol. Self-consistent field theory (SCFT) calculations corroborate the presence of DG networks at intermediate compositions for AB1B2 miktoarm triblock polymers, although no specific B1/B2 ratio is predicted to significantly broaden the network phase window. This study highlights the role of asymmetry in the molecular design of amphiphilic block oligomers, which enables the stabilization of network morphologies with ultrasmall feature sizes over a wide composition range.

Grand canonical Monte Carlo (GCMC) simulations were used to investigate pore filling and hysteresis in nanoporous metal-organic frameworks (MOFs). Adsorption and desorption isotherms were calculated for argon at 87 K in 1866 MOFs from the CoRE MOF database and for short n-alkanes in selected MOFs, keeping the adsorbent structure rigid. Analysis of the molecular configurations showed two different mechanisms and origins of hysteresis: one involving a transition of the adsorbate arrangement in the pores similar to a gas-to-liquid transition associated with a large change in the loading and one more similar to a liquid-to-solid transition associated with a relatively small change in the loading. Our GCMC simulations in MOFs with diverse pore topologies indicate exceptions to an empirical relationship for the minimum diameter of a cylindrical pore required for hysteresis as a function of the adsorbate diameter and reduced temperature. The simulations reveal some structures where isotherms exhibit two steps in the adsorption branch and only one step in the desorption branch. Hysteresis loops with different numbers of adsorption and desorption steps are not common. To better understand why hysteresis is observed in the GCMC simulations, the concept of the transition probability for observing a step in the adsorption isotherm at a given pressure in a GCMC simulation is introduced. We used two different methods to calculate the transition probabilities and found that these yielded comparable results. The transition probability provides a measure of the length of GCMC simulations to yield reliable results.

Water adsorption isotherms from 25 to 125 degrees C were measured for three metal-organic frameworks (MOFs), MOF-303, MOF-LA2-1, and MIL-100(Fe), which are frequently studied for water harvesting applications. The results show how the step in the water adsorption isotherm varies as a function of temperature and detail the combination of pressure and temperature necessary to remove adsorbed water. Furthermore, isobaric-isothermal Gibbs ensemble Monte Carlo simulations performed for MOF-303 shed light on the change in occupation numbers of the different known water adsorption sites with increasing temperature. Additionally, the diffusion rates of water through these materials were measured using concentration swing frequency response, and micropore diffusion was identified as the controlling mechanism. The Darken relation was used to show the dependence of the diffusion rate on the concentration and the impact of the adsorption isotherm slope. The adsorption of water on MOF-LA2-1 is faster than that on MIL-100(Fe). These data show that MOF-LA2-1 with its high-water adsorption capacity, quick adsorption rate, and favorable desorption energetics is a leading candidate for atmospheric water harvesting.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTArdila Hayu Tiwikrama Wins the Inaugural Journal of Chemical & Engineering Data Early Career AwardJ. Ilja Siepmann*J. Ilja SiepmannMore by J. Ilja Siepmannhttps://orcid.org/0000-0003-2534-4507 and John SandersJohn SandersMore by John Sandershttps://orcid.org/0000-0001-7565-6758Cite this: J. Chem. Eng. Data 2024, 69, 1, 1–2Publication Date (Web):January 11, 2024Publication History Received20 December 2023Published online11 January 2024Published inissue 11 January 2024https://pubs.acs.org/doi/10.1021/acs.jced.3c00761https://doi.org/10.1021/acs.jced.3c00761editorialACS PublicationsCopyright © Published 2024 by American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views790Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (4 MB) Get e-AlertscloseSUBJECTS:Alcohols,Bioengineering and biotechnology,Chemical engineering and industrial chemistry,Ketones,Phase equilibria Get e-Alerts

The speed of sound in bubbly water is an important parameter in the wave equations governing pressure-density relations for turbulent multi-phase flow simulations. Recent molecular simulation results indicate that, for bubbles that are thermodynamically stable at finite volume conditions, the derivative of total pressure P with density rho has a negative sign, complicating the interpretation of the speed of sound. We show that such a negative compressibility is thermodynamically consistent in a single-component two-phase model at finite volume, and identify an empirically derived equation of state to illustrate that this observation is not an artifact of small simulation length scales. To reconcile this thermodynamic relation with measurements of sound propagation, we decompose the derivative partial derivative P/partial derivative rho for bubbly water into its constituent phases to identify absorptive and transmissive contributors, both with an equation of state and using molecular simulations. We find that the speed of sound in the liquid phase remains real-valued while the bubble attenuates sound, giving a negative system compressibility. The inclusion of N2 molecules in molecular simulations illustrates that these observations are robust and hold also for mixtures. From these simulations, we also compute scattering functions for bubbly systems to identify oscillations associated with the speed of sound. Finally, the spherical harmonic modes of bubble oscillations are analyzed in the context of resonance with propagating waves.

Using knowledge from statistical thermodynamics and crystallography, we develop an image-image translation model, called SorbIIT, that uses three-dimensional grids of adsorbate-adsorbent interaction energies as input to predict the spatially resolved loading surface of nanoporous materials over a broad range of temperatures and pressures. SorbIIT consists of a closed-form differential model for loading-surface prediction and a U-Net to generate spatial differential distributions from the energy grids. SorbIIT is trained using the energy grids and adsorbate distributions (obtained from high-throughput simulations) of 50 synthesized and 70 hypothetical zeolites and applied for predicting the adsorption of carbon dioxide, hydrogen sulfide, n-butane, 2-methylpropane, krypton, and xenon in other zeolites from 256 to 400 K. Employing a quadratic isotherm model for the local differentiation, SorbIIT yields mean R-2 values of 0.998 for total adsorption and 0.6904 for local adsorption with a resolution of 0.2 & Aring;, and a value of 0.721 for the structural similarity of the local loading distribution.

Zeolitic imidazolate framework (ZIF-8) is a promising material for gas separation applications. It also serves as a prototype for numerous ZIFs, including amorphous ones, with a broader range of possible applications, including sensors, catalysis, and lithography. It consists of zinc coordinated with 2-methylimidazolate (2mIm) and has been synthesized with methods ranging from liquid-phase to solvent-free synthesis, which aim to control its crystal size and shape, film thickness and microstructure, and incorporation into nanocomposites. Depending on the synthesis method and postsynthesis treatments, ZIF-8 materials may deviate from the nominal defect-free ZIF-8 crystal structure due to defects like missing 2mIm, missing zinc, and physically adsorbed 2mIm trapped in the ZIF-8 pores, which may alter its performance and stability. Infrared (IR) spectroscopy has been used to assess the presence of defects in ZIF-8 and related materials. However, conflicting interpretations by various authors persist in the literature. Here, we systematically investigate ZIF-8 vibrational spectra by combining experimental IR spectroscopy and first-principles molecular dynamics simulations, focusing on assigning peaks and elucidating the spectroscopic signals of putative defects present in the ZIF-8 material. We attempt to resolve conflicting assignments from the literature and to provide a comprehensive understanding of the vibrational spectra of ZIF-8 and its defect-induced variations, aiming toward more precise quality control and design of ZIF-8-based materials for emerging applications.

Bicontinuous thermotropic liquid crystal (LC) materials, e.g., double gyroid (DG) phases, have garnered significant attention due to the potential utility of their 3D network structures in wide-ranging applications. However, the utility of these materials is significantly constrained by the lack of robust molecular design rules for shape-filling amphiphiles that spontaneously adopt the saddle curvatures required to access these useful supramolecular assemblies. Toward this aim, we synthesized anomerically pure Guerbet-type glycolipids bearing cellobiose head groups and branched alkyl tails and studied their thermotropic LC self-assembly. Using a combination of differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray scattering, our studies demonstrate that Guerbet cellobiosides exhibit a strong propensity to self-assemble into DG morphologies over wide thermotropic phase windows. The stabilities of these assemblies sensitively depend on the branched alkyl tail structure and the anomeric configuration of the glycolipid in a previously unrecognized manner. Complementary molecular simulations furnish detailed insights into the observed self-assembly characteristics, thus unveiling molecular motifs that foster network phase self-assembly that will enable future designs and applications of network LC materials.

Silica particles are widely used as a support material for chemically-bound stationary phases in chromatographic separation processes. The tuning of textural properties and surface chemistry of stationary phase materials (SPMs) is crucial to enhance their selectivity to certain compounds and the efficiency of the separation process. Silica supports have the advantage that their surface can be modified with a large variety of hydrophilic and hydrophobic functional groups, but their influence on the silica surface properties has not been evaluated in detail. In this sense, the contact angle is a key parameter for the assessment of surface chemistry but its quantification in the pore walls is particularly challenging and requires a combination of various tools and experimental techniques. In this work we demonstrate that by combining water adsorption and intrusion measurements is possible to derive reliable information of the effective contact angle θ of adsorbed water for wetting (θ = 0°), partial wetting (θ < 90°), and non-wetting situations (θ > 90°) observed on the pore walls of the SPMs under study. Furthermore, NMR relaxometry experiments reveal that the T1,ads.film/T2,ads.film-ratio can be correlated with the effective adsorption strength of water on the surface. Indeed, we find a linear correlation between the negative inverse of the T1,ads.film/T2,ads.film -ratio (-T2,ads.film/T1,ads.film) with the contact angle determined from water vapor adsorption and intrusion experiments for the investigated SPMs. Our work clearly demonstrates for the first time that water vapor adsorption experiments and novel water intrusion technique coupled with NMR relaxometry can be used as complementary techniques to quantitatively analyze the wettability behavior and surface chemistry of nanoporous materials.

Molecular dynamics simulations in the microcanonical ensemble are performed to study the collapse of a bubble in liquid water using the single-site mW and the four-site TIP4P/2005 water models. To study system size effects, simulations for pure water systems are performed using periodically replicated simulation boxes with linear dimensions, L, ranging from 32 to 512 nm with the largest systems containing 8.7 x 10(6) and 4.5 x 10(9) molecules for the TIP4P/2005 and mW water models, respectively. The computationally more efficient mW water model allows us to reach converging behavior when the bubble dynamics results are plotted in reduced units, and the limiting behavior can be obtained through linear extrapolation in L-1. Qualitative differences are observed between simulations with the mW and TIP4P/2005 water models, but they can be explained by the models' differences in predicted viscosity and surface tension. Although bubble collapse occurs on time scales of only hundreds of picoseconds, the system sizes used here are sufficiently large to obtain bubble dynamics consistent with the Rayleigh-Plesset equation when using the models' thermophysical properties as input. For the conditions explored here, extreme heating of the interfacial water molecules near the time of collapse is observed for the larger mW water systems (but the model underpredicts the viscosity), whereas heating is less pronounced for the TIP4P/2005 water systems because its larger viscosity contribution slows the collapse dynamics. The presence of nitrogen within the bubble only starts to affect bubble dynamics near the very end of the initial collapse, leading to an incomplete collapse and strong rebound for the mW water model. Although nitrogen is non-condensable at 300 K, it becomes highly compressed and reaches a liquid-like density near the collapse point. We find that the dissolution of nitrogen is much slower than the movement of the collapsing water front, and the re-expansion of the dense nitrogen droplet gives rise to bubble rebound. The incompatibility of the collapse and dissolution time scales should be considered for continuum-scale modeling of bubble dynamics. We also confirm that the diffusion coefficient for dissolved nitrogen is insensitive to pressure as the liquid transitions from a compressed to a stretched state.