Halogen-Decorated Metal-Organic Frameworks for Efficient and Selective CO2 Capture, Separation, and Chemical Fixation with Epoxides under Mild Conditions.

In the present work, three novel halogen-appended cadmium(II) metal-organic frameworks [Cd2(L1)2(4,4'-Bipy)2]n·4n(DMF) (1), [Cd2(L2)2(4,4'-Bipy)2]n·3n(DMF) (2), and [Cd(L3)(4,4'-Bipy)]n·2n(DMF) (3) [where L1 = 5-{(4-bromobenzyl)amino}isophthalate; L2 = 5-{(4-chlorobenzyl)amino}isophthalate; L3 = 5-{(4-fluorobenzyl)amino}isophthalate; 4,4'-Bipy = 4,4'-bipyridine; and DMF = N,N'-dimethylformamide] have been synthesized under solvothermal conditions and characterized by various analytical techniques. The single-crystal X-ray diffraction analysis demonstrated that all the MOFs feature a similar type of three-dimensional structure having a binuclear [Cd2(COO)4(N)4] secondary building block unit. Moreover, MOFs 1 and 2 contain one-dimensional channels along the b-axis, whereas MOF 3 possesses a 1D channel along the a-axis. In these MOFs, the pores are decorated with multifunctional groups, i.e., halogen and amine. The gas adsorption analysis of these MOFs demonstrate that they display high uptake of CO2 (up to 5.34 mmol/g) over N2 and CH4. The isosteric heat of adsorption (Qst) value for CO2 at zero loadings is in the range of 18-26 kJ mol-1. In order to understand the mechanism behind the better adsorption of CO2 by our MOFs, we have also performed configurational bias Monte Carlo simulation studies, which confirm that the interaction between our MOFs and CO2 is stronger compared to those with N2 and CH4. Various noncovalent interactions, e.g., halogen (X)···O, Cd···O, and O···O, between CO2 and the halogen atom, the Cd(II) metal center, and the carboxylate group from the MOFs are observed, respectively, which may be a reason for the higher carbon dioxide adsorption. Ideal adsorbed solution theory (IAST) calculations of MOF 1 demonstrate that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85) are ca. 28 and 193 at 273 K, respectively. However, upon increasing the temperature to 298 K, the selectivity value (S = 34) decreases significantly for the CO2/N2 mixture. We have also calculated the breakthrough analysis curves for all the MOFs using mixtures of CO2/CH4 (50:50) and CO2/N2 (50:50 and 15:85) at different entering gas velocities and observed larger retention times for CO2 in comparison with other gases, which also signifies the stronger interaction between our MOFs and CO2. Moreover, due to the presence of Lewis acidic metal centers, these MOFs act as heterogeneous catalysts for the CO2 fixation reactions with different epoxides in the presence of tetrabutyl ammonium bromide (TBAB), for conversion into industrially valuable cyclic carbonates. These MOFs exhibit a high conversion (96-99%) of epichlorohydrin (ECH) to the corresponding cyclic carbonate 4-(chloromethyl)-1,3-dioxolan-2-one after 12 h of reaction time at 1 bar of CO2 pressure, at 65 °C. The MOFs can be reused up to four cycles without compromising their structural integrity as well as without losing their activity significantly.

Mixing I and Br in Inorganic Perovskites: Atomistic Insights from Reactive Molecular Dynamics Simulations.

All-inorganic halide perovskites have received a great deal of attention as attractive alternatives to overcome the stability issues of hybrid halide perovskites that are commonly associated with organic cations. To find a compromise between the optoelectronic properties of CsPbI3 and CsPbBr3, perovskites with CsPb(BrxI1-x)3 mixed compositions are commonly used. An additional benefit is that without sacrificing the optoelectronic properties for applications such as solar cells or light-emitting diodes, small amounts of Br in CsPbI3 can prevent the inorganic perovskite from degrading to a photo-inactive non-perovskite yellow phase. Despite indications that strain in the perovskite lattice plays a role in the stabilization of the material, a full understanding of such strain is lacking. Here, we develop a reactive force field (ReaxFF) for perovskites starting from our previous work for CsPbI3, and we extend this force field to CsPbBr3 and mixed CsPb(BrxI1-x)3 compounds. This force field is used in large-scale molecular dynamics simulations to study perovskite phase transitions and the internal ion dynamics associated with the phase transitions. We find that an increase of the Br content lowers the temperature at which the perovskite reaches a cubic structure. Specifically, by substituting Br for I, the smaller ionic radius of Br induces a strain in the lattice that changes the internal dynamics of the octahedra. Importantly, this effect propagates through the perovskite lattice ranging up to distances of 2 nm, explaining why small concentrations of Br in CsPb(BrxI1-x)3 (x ≤ 1/4) have a significant impact on the phase stability of mixed halide perovskites.

Combination of frequency- and time-domain characteristics of the fibrillatory waves for enhanced prediction of persistent atrial fibrillation recurrence after catheter ablation.

Catheter ablation (CA) remains the cornerstone alternative to cardioversion for sinus rhythm (SR) restoration in patients with atrial fibrillation (AF). Unfortunately, despite the last methodological and technological advances, this procedure is not consistently effective in treating persistent AF. Beyond introducing new indices to characterize the fibrillatory waves (f-waves) recorded through the preoperative electrocardiogram (ECG), the aim of this study is to combine frequency- and time-domain features to improve CA outcome prediction and optimize patient selection for the procedure, given the absence of any study that jointly analyzes information from both domains. Precisely, the f-waves of 151 persistent AF patients undergoing their first CA procedure were extracted from standard V1 lead. Novel spectral and amplitude features were derived from these waves and combined through a machine learning algorithm to anticipate the intervention mid-term outcome. The power rate index (φ), which estimates the power of the harmonic content regarding the dominant frequency (DF), yielded the maximum individual discriminant ability of 64% to discern between individuals who experienced a recurrence of AF and those who sustained SR after a 9-month follow-up period. The predictive accuracy was improved up to 78.5% when this parameter φ was merged with the amplitude spectrum area in the DF bandwidth (AMSALF) and the normalized amplitude of the f-waves into a prediction model based on an ensemble classifier, built by random undersampling boosting of decision trees. This outcome suggests that the synthesis of both spectral and temporal features of the f-waves before CA might enrich the prognostic knowledge of this therapy for persistent AF patients.

Correction: How fast do defects migrate in halide perovskites: insights from on-the-fly machine-learned force fields.

Correction for 'How fast do defects migrate in halide perovskites: insights from on-the-fly machine-learned force fields' by Mike Pols et al., Chem. Commun., 2023, 59, 4660-4663, https://doi.org/10.1039/D3CC00953J.

Symptom burden guiding invasive electrophysiological study in paroxysmal supraventricular tachycardia: The believe SVT registry.

BACKGROUND AND OBJECTIVE: Patients with palpitations clinically suggestive of paroxysmal supraventricular tachycardia (PSVT) are often managed conservatively until ECG-documentation of the tachycardia, leading to high impact on life quality and healthcare resource utilization. We evaluated results of electrophysiological study (EPS), and ablation when appropriate, among these patients, with special focus on gender differences in management. METHODS: BELIEVE SVT is a European multicenter, retrospective registry in tertiary hospitals performing EPS in patients with palpitations, without ECG-documentation of tachycardia or preexcitation, and considered highly suggestive of PSVT by a cardiologist or cardiac electrophysiologist. We analyzed clinical characteristics, results of EPS and ablation, complications, and clinical outcomes during follow-up. RESULTS: Six-hundred eighty patients from 20 centers were included. EPS showed sustained tachycardia in 60.9% of patients, and substrate potentially enabling AVNRT in 14.7%. No major/permanent complications occurred. Minor/transient complications were reported in 0.84% of patients undergoing diagnostic-only EPS and 1.8% when followed by ablation. During a 3.4-year follow-up, 76.2% of patients remained free of palpitations recurrence. Ablation (OR: 0.34, P < .01) and male gender (OR: 0.58, P = .01) predicted no recurrence. Despite a higher female proportion among patients with recurrence, (77.2% vs 63.5% among those asymptomatic during follow-up, P < .01), 73% of women in this study reported no recurrence of palpitations after EPS. CONCLUSIONS: EPS and ablation are safe and effective in preventing recurrence of nondocumented palpitations clinically suggestive of PSVT. Despite a lower efficacy, this strategy is also highly effective among women and warrants no gender differences in management.

TAMOF-1 as a Versatile and Predictable Chiral Stationary Phase for the Resolution of Racemic Mixtures.

Metal-organic frameworks (MOFs) have become promising materials for multiple applications due to their controlled dimensionality and tunable properties. The incorporation of chirality into their frameworks opens new strategies for chiral separation, a key technology in the pharmaceutical industry as each enantiomer of a racemic drug must be isolated. Here, we describe the use of a combination of computational modeling and experiments to demonstrate that high-performance liquid chromatography (HPLC) columns packed with TAMOF-1 as the chiral stationary phase are efficient, versatile, robust, and reusable with a wide array of mobile phases (polar and non-polar). As proof of concept, in this article, we report the resolution with TAMOF-1 HPLC columns of nine racemic mixtures with different molecular sizes, geometries, and functional groups. Initial in silico studies allowed us to predict plausible separations in chiral compounds from different families, including terpenes, calcium channel blockers, or P-stereogenic compounds. The experimental data confirmed the validity of the models and the robust performance of TAMOF-1 columns. The added value of in silico screening is an unprecedented achievement in chiral chromatography.

The Boost of Toluene Capture in UiO-66 Triggered by Structural Defects or Air Humidity.

This work aimed to investigate the adsorption of toluene in UiO-66 materials. Toluene is a volatile, aromatic organic molecule that is recognized as the main component of VOCs. These compounds are harmful to the environment as well as to living organisms. One of the materials that allows the capture of toluene is the UiO-66. A satisfactory representation of the calculated isotherm steep front and sorption capacity compared to the experiment was obtained by reducing the force field σ parameter by 5% and increasing ε by 5%. Average occupation profiles, which are projections of the positions of molecules during pressure increase, as well as RDFs, which are designed to determine the distance of the center of mass of the toluene molecule from organic linkers and metal clusters, respectively, made it possible to explain the mechanism of toluene adsorption on the UiO-66 material.

An Efficient Strategy for Electroreduction Reactor Outlet Fractioning into Valuable Products.

In this work, two industrial dual-step pressure swing adsorption (PSA) processes were designed and simulated to obtain high-purity methane, CO2, and syngas from a gas effluent of a CO2 electroreduction reactor using different design configurations. Among the set of zeolites that was investigated using Monte Carlo and molecular dynamics simulations, NaX and MFI were the ones selected. The dual-PSA process for case study 1 is only capable of achieving a 90.5% methane purity with a 95.2% recovery. As for case study 2, methane is obtained with a 97.5% purity and 95.3% recovery. Both case studies can produce CO2 with high purity and recovery (>97 and 95%, respectively) and syngas with a H2/CO ratio above 4. Although case study 2 allows methane to be used as domestic gas, a much higher value for its energy consumption is observed compared to case study 1 (64.9 vs 29.8 W h molCH4-1).

How fast do defects migrate in halide perovskites: insights from on-the-fly machine-learned force fields.

The migration of defects plays an important role in the stability of halide perovskites. It is challenging to study defect migration with experiments or conventional computer simulations. The former lacks an atomic-scale resolution and the latter suffers from short simulation times or a lack of accuracy. Here, we demonstrate that machine-learned force fields, trained with an on-the-fly active learning scheme against accurate density functional theory calculations, allow us to probe the differences in the dynamical behaviour of halide interstitials and halide vacancies in two closely related compositions CsPbI3 and CsPbBr3. We find that interstitials migrate faster than vacancies, due to the shorter migration paths of interstitials. Both types of defects migrate faster in CsPbI3 than in CsPbBr3. We attribute this to the less compact packing of the ions in CsPbI3, which results in a larger motion of the ions and thus more frequent defect migration jumps.

On the Use of Water and Methanol with Zeolites for Heat Transfer.

Reducing carbon dioxide emissions has become a must in society, making it crucial to find alternatives to supply the energy demand. Adsorption-based cooling and heating technologies are receiving attention for thermal energy storage applications. In this paper, we study the adsorption of polar working fluids in hydrophobic and hydrophilic zeolites by means of experimental quasi-equilibrated temperature-programmed desorption and adsorption combined with Monte Carlo simulations. We measured and computed water and methanol adsorption isobars in high-silica HS-FAU, NaY, and NaX zeolites. We use the experimental adsorption isobars to develop a set of parameters to model the interaction between methanol and the zeolite and cations. Once we have the adsorption of these polar molecules, we use a mathematical model based on the adsorption potential theory of Dubinin-Polanyi to assess the performance of the adsorbate-working fluids for heat storage applications. We found that molecular simulations are an excellent tool for investigating energy storage applications since we can reproduce, complement, and extend experimental observations. Our results highlight the importance of controlling the hydrophilic/hydrophobic nature of the zeolites by changing the Al content to maximize the working conditions of the heat storage device.

Solubility of CO2 in Aqueous Formic Acid Solutions and the Effect of NaCl Addition: A Molecular Simulation Study.

There is a growing interest in the development of routes to produce formic acid from CO2, such as the electrochemical reduction of CO2 to formic acid. The solubility of CO2 in the electrolyte influences the production rate of formic acid. Here, the dependence of the CO2 solubility in aqueous HCOOH solutions with electrolytes on the composition and the NaCl concentration was studied by Continuous Fractional Component Monte Carlo simulations at 298.15 K and 1 bar. The chemical potentials of CO2, H2O, and HCOOH were obtained directly from single simulations, enabling the calculation of Henry coefficients and subsequently considering salting in or salting out effects. As the force fields for HCOOH and H2O may not be compatible due to the presence of strong hydrogen bonds, the Gibbs-Duhem integration test was used to test this compatibility. The combination of the OPLS/AA force field with a new set of parameters, in combination with the SPC/E force field for water, was selected. It was found that the solubility of CO2 decreases with increasing NaCl concentration in the solution and increases with the increase of HCOOH concentration. This continues up to a certain concentration of HCOOH in the solution, after which the CO2 solubility is high and the NaCl concentration has no significant effect.

Preoperative Prediction of Catheter Ablation Outcome in Persistent Atrial Fibrillation Patients through Spectral Organization Analysis of the Surface Fibrillatory Waves.

Catheter ablation (CA) is a commonly used treatment for persistent atrial fibrillation (AF). Since its medium/long-term success rate remains limited, preoperative prediction of its outcome is gaining clinical interest to optimally select candidates for the procedure. Among predictors based on the surface electrocardiogram, the dominant frequency (DF) and harmonic exponential decay (γ) of the fibrillatory waves (f-waves) have reported promising but clinically insufficient results. Hence, the main goal of this work was to conduct a broader analysis of the f-wave harmonic spectral structure to improve CA outcome prediction through several entropy-based measures computed on different frequency bands. On a database of 151 persistent AF patients under radio-frequency CA and a follow-up of 9 months, the newly introduced parameters discriminated between patients who relapsed to AF and those who maintained SR at about 70%, which was statistically superior to the DF and approximately similar to γ. They also provided complementary information to γ through different combinations in multivariate models based on lineal discriminant analysis and report classification performance improvement of about 5%. These results suggest that the presence of larger harmonics and a proportionally smaller DF peak is associated with a decreased probability of AF recurrence after CA.

What Happens at Surfaces and Grain Boundaries of Halide Perovskites: Insights from Reactive Molecular Dynamics Simulations of CsPbI3.

The commercialization of perovskite solar cells is hindered by the poor long-term stability of the metal halide perovskite (MHP) light-absorbing layer. Solution processing, the common fabrication method for MHPs, produces polycrystalline films with a wide variety of defects, such as point defects, surfaces, and grain boundaries. Although the optoelectronic effects of such defects have been widely studied, the evaluation of their impact on the long-term stability remains challenging. In particular, an understanding of the dynamics of degradation reactions at the atomistic scale is lacking. In this work, using reactive force field (ReaxFF) molecular dynamics simulations, we investigate the effects of defects, in the forms of surfaces, surface defects, and grain boundaries, on the stability of the inorganic halide perovskite CsPbI3. Our simulations establish a stability trend for a variety of surfaces, which correlates well with the occurrence of these surfaces in experiments. We find that a perovskite surface degrades by progressively changing the local geometry of PbIx octahedra from corner- to edge- to face-sharing. Importantly, we find that Pb dangling bonds and the lack of steric hindrance of I species are two crucial factors that induce degradation reactions. Finally, we show that the stability of these surfaces can be modulated by adjusting their atomistic details, by either creating additional point defects or merging them to form grain boundaries. While in general additional defects, particularly when clustered, have a negative impact on the material stability, some grain boundaries have a stabilizing effect, primarily because of the additional steric hindrance.

Separation of Volatile Organic Compounds in TAMOF-1.

Separation of volatile organic compounds is one of the most studied processes in industry. TAMOF-1 is a homochiral metal-organic framework with a crystalline network of interconnected ≈1 nm channels and has high thermal and chemical stability. Thanks to these features, it can resolve racemic mixtures of chiral drugs as a chiral stationary phase in chromatography. Interestingly, the particular shape and size of its channels, along with the presence of metallic centers and functional groups, allow establishing weak but significant interactions with guest molecules. This opens interesting possibilities not only to resolve racemates but also to separate other organic mixtures, such as saturated/unsaturated and/or linear/branched molecules. In search of these applications, we have studied the separation of volatile organic compounds in TAMOF-1. Monte Carlo simulations in the grand-canonical ensemble have been carried out to evaluate the separation of the selected molecules. Our results predict that TAMOF-1 is able to separate xylene isomers, hexane isomers, and benzene-cyclohexane mixtures. Experimental breakthrough analysis in the gas phase and also in the liquid phase confirms these predictions. Beds of TAMOF-1 are able to recognize the substitution in xylenes and the branching in hexanes, yielding excellent separation and reproducibility, thanks to the chemical and mechanical features of this material.

Revisiting Vibrational Spectroscopy to Tackle the Chemistry of Zr6O8 Metal-Organic Framework Nodes.

The metal-organic framework MOF-808 contains Zr6O8 nodes with a high density of vacancy sites, which can incorporate carboxylate-containing functional groups to tune chemical reactivity. Although the postsynthetic methods to modify the chemistry of the Zr6O8 nodes in MOFs are well known, tackling these alterations from a structural perspective is still a challenge. We have combined infrared spectroscopy experiments and first-principles calculations to identify the presence of node vacancies accessible for chemical modifications within the MOF-808. We demonstrate the potential of our approach to assess the decoration of MOF-808 nodes with different catechol-benzoate ligands. Furthermore, we have applied advanced synchrotron characterization tools, such as pair distribution function analyses and X-ray absorption spectroscopy, to resolve the atomic structure of single metal sites incorporated into the catechol groups postsynthetically. Finally, we demonstrate the catalytic activity of these MOF-808 materials decorated with single copper sites for 1,3-dipolar cycloadditions.

Challenges of modeling nanostructured materials for photocatalytic water splitting.

Understanding the water splitting mechanism in photocatalysis is a rewarding goal as it will allow producing clean fuel for a sustainable life in the future. However, identifying the photocatalytic mechanisms by modeling photoactive nanoparticles requires sophisticated computational techniques based on multiscale modeling. In this review, we will survey the strengths and drawbacks of currently available theoretical methods at different length and accuracy scales. Understanding the surface-active site through Density Functional Theory (DFT) using new, more accurate exchange-correlation functionals plays a key role for surface engineering. Larger scale dynamics of the catalyst/electrolyte interface can be treated with Molecular Dynamics albeit there is a need for more generalizations of force fields. Monte Carlo and Continuum Modeling techniques are so far not the prominent path for modeling water splitting but interest is growing due to the lower computational cost and the feasibility to compare the modeling outcome directly to experimental data. The future challenges in modeling complex nano-photocatalysts involve combining different methods in a hierarchical way so that resources are spent wisely at each length scale, as well as accounting for excited states chemistry that is important for photocatalysis, a path that will bring devices closer to the theoretical limit of photocatalytic efficiency.

Defect-induced tuning of polarity-dependent adsorption in hydrophobic-hydrophilic UiO-66.

Structural defects in metal-organic frameworks can be exploited to tune material properties. In the case of UiO-66 material, they may change its nature from hydrophobic to hydrophilic and therefore affect the mechanism of adsorption of polar and non-polar molecules. In this work, we focused on understanding this mechanism during adsorption of molecules with different dipole moments, using the standard volumetric adsorption measurements, IR spectroscopy, DFT + D calculations, and Monte Carlo calculations. Average occupation profiles showed that polar and nonpolar molecules change their preferences for adsorption sites. Hence, defects in the structure can be used to tune the adsorption properties of the MOF as well as to control the position of the adsorbates within the micropores of UiO-66.

New Features of the Open Source Monte Carlo Software Brick-CFCMC: Thermodynamic Integration and Hybrid Trial Moves.

We present several new major features added to the Monte Carlo (MC) simulation code Brick-CFCMC for phase- and reaction equilibria calculations (https://gitlab.com/ETh_TU_Delft/Brick-CFCMC). The first one is thermodynamic integration for the computation of excess chemical potentials (µex). For this purpose, we implemented the computation of the ensemble average of the derivative of the potential energy with respect to the scaling factor for intermolecular interactions (⟨∂U∂λ⟩). Efficient bookkeeping is implemented so that the quantity ∂U∂λ is updated after every MC trial move with negligible computational cost. We demonstrate the accuracy and reliability of the calculation of µex for sodium chloride in water. Second, we implemented hybrid MC/MD translation and rotation trial moves to increase the efficiency of sampling of the configuration space. In these trial moves, short Molecular Dynamics (MD) trajectories are performed to collectively displace or rotate all molecules in the system. These trajectories are accepted or rejected based on the total energy drift. The efficiency of these trial moves can be tuned by changing the time step and the trajectory length. The new trial moves are demonstrated using MC simulations of a viscous fluid (deep eutectic solvent).

Carbon Dioxide Capture Enhanced by Pre-Adsorption of Water and Methanol in UiO-66.

The rapidly rising level of carbon dioxide in the atmosphere resulting from human activity is one of the greatest environmental problems facing our civilization today. Most technologies are not yet sufficiently developed to move existing infrastructure to cleaner alternatives. Therefore, techniques for capturing carbon dioxide from emission sources may play a key role at the moment. The structure of the UiO-66 material not only meets the requirement of high stability in contact with water vapor but through the water pre-adsorbed in the pores, the selectivity of carbon dioxide adsorption is increased. We successfully applied the recently developed methodology for water adsorption modelling. It allowed to elucidate the influence of water on CO2 adsorption and study the mechanism of this effect. We showed that water is adsorbed in octahedral cage and stands for promotor for CO2 adsorption in less favorable space than tetrahedral cages. Water plays a role of a mediator of adsorption, what is a general idea of improving affinity of adsorbate. On the basis of pre-adsorption of methanol as another polar solvent, we have shown that the adsorption sites play a key role here, and not, as previously thought, only the interaction between the solvent and quadrupole carbon dioxide. Overall, we explained the mechanism of increased CO2 adsorption in the presence of water and methanol, as polar solvents, in the UiO-66 pores for a potential post-combustion carbon dioxide capture application.

In Silico Screening of Zeolites for High-Pressure Hydrogen Drying.

According to the ISO 14687-2:2019 standard, the water content of H2 fuel for transportation and stationary applications should not exceed 5 ppm (molar). To achieve this water content, zeolites can be used as a selective adsorbent for water. In this work, a computational screening study is carried out for the first time to identify potential zeolite frameworks for the drying of high-pressure H2 gas using Monte Carlo (MC) simulations. We show that the Si/Al ratio and adsorption selectivity have a negative correlation. 218 zeolites available in the database of the International Zeolite Association are considered in the screening. We computed the adsorption selectivity of each zeolite for water from the high-pressure H2 gas having water content relevant to vehicular applications and near saturation. It is shown that due to the formation of water clusters, the water content in the H2 gas has a significant effect on the selectivity of zeolites with a helium void fraction larger than 0.1. Under each operating condition, five most promising zeolites are identified based on the adsorption selectivity, the pore limiting diameter, and the volume of H2 gas that can be dried by 1 dm3 of zeolite. It is shown that at 12.3 ppm (molar) water content, structures with helium void fractions smaller than 0.07 are preferred. The structures identified for 478 ppm (molar) water content have helium void fractions larger than 0.26. The proposed zeolites can be used to dry 400-8000 times their own volume of H2 gas depending on the operating conditions. Our findings strongly indicate that zeolites are potential candidates for the drying of high-pressure H2 gas.