Molecular Accessibility and Diffusion of Resorufin in Zeolite Crystals.

Invited for the cover of this issue is the group of Professor Bert Weckhuysen at Utrecht University. The image depicts the change in fluorescence color of a resorufin dye molecule when it is protonated and confined inside the micropores of zeolite-ß. Read the full text of the article at 10.1002/chem.202302553.

Molecular Accessibility and Diffusion of Resorufin in Zeolite Crystals.

We have used confocal laser scanning microscopy on the small, fluorescent resorufin dye molecule to visualize molecular accessibility and diffusion in the hierarchical, anisotropic pore structure of large (~10 µm-sized) zeolite-ß crystals. The resorufin dye is widely used in life and materials science, but only in its deprotonated form because the protonated molecule is barely fluorescent in aqueous solution. In this work, we show that protonated resorufin is in fact strongly fluorescent when confined within zeolite micropores, thus enabling fluorescence microimaging experiments. We find that J-aggregation guest-guest interactions lead to a decrease in the measured fluorescence intensity that can be prevented by using non-fluorescent spacer molecules. We characterized the pore space by introducing resorufin from the outside solution and following its diffusion into zeolite-ß crystals. The eventual homogeneous distribution of resorufin molecules throughout the zeolite indicates a fully accessible pore network. This enables the quantification of the diffusion coefficient in the straight pores of zeolite-ß without the need for complex analysis, and we found a value of 3×10-15  m2  s-1 . Furthermore, we saw that diffusion through the straight pores of zeolite-ß is impeded when crossing the boundaries between zeolite subunits.

Understanding the Effects of Binders in Gas Sorption and Acidity of Aluminium Fumarate Extrudates.

Understanding the impact of shaping processes on solid adsorbents is critical for the implementation of MOFs in industrial separation processes or as catalytic materials. Production of MOF-containing shaped particles is typically associated with loss of porosity and modification of acid sites, two phenomena that affect their performance. Herein, we report a detailed study on how extrusion affects the crystallinity, porosity, and acidity of the aluminium fumarate MOF with clays or SiO2 gel binders. Thorough characterization showed that the clay binders confer the extrudates a good mechanical robustness at the expense of porosity, while silica gel shows an opposite trend. The CO2 selectivity towards CH4 , of interest for natural gas separation processes, is maintained upon the extrusion process. Moreover, probe FTIR spectroscopy revealed no major changes in the types of acid sites. This study highlights that these abundant and inexpensive clay materials may be used for scaling MOFs as active adsorbents.

Unravelling Channel Structure-Diffusivity Relationships in Zeolite ZSM-5 at the Single-Molecule Level.

The development of improved zeolite materials for applications in separation and catalysis requires understanding of mass transport. Herein, diffusion of single molecules is tracked in the straight and sinusoidal channels of the industrially relevant ZSM-5 zeolites using a combination of single-molecule localization microscopy and uniformly oriented zeolite thin films. Distinct motion behaviors are observed in zeolite channels with the same geometry, suggesting heterogeneous guest-host interactions. Quantification of the diffusion heterogeneities in the sinusoidal and straight channels suggests that the geometry of zeolite channels dictates the mobility and motion behavior of the guest molecules, resulting in diffusion anisotropy. The study of hierarchical zeolites shows that the addition of secondary pore networks primarily enhances the diffusivity of sinusoidal zeolite channels, and thus alleviating the diffusion limitations of microporous zeolites.

Influence of Pore Structure and Metal-Node Geometry on the Polymerization of Ethylene over Cr-Based Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) have received increasing interest as solid single-site catalysts, owing to their tunable pore architecture and metal node geometry. The ability to exploit these modulators makes them prominent candidates for producing polyethylene (PE) materials with narrow dispersity index (Ð) values. Here a study is presented in which the ethylene polymerization properties, with Et2 AlCl as activator, of three renowned Cr-based MOFs, MIL-101(Cr)-NDC (NDC=2,6-dicarboxynapthalene), MIL-53(Cr) and HKUST-1(Cr), are systematically investigated. Ethylene polymerization reactions revealed varying catalytic activities, with MIL-101(Cr)-NDC and MIL-53(Cr) being significantly more active than HKUST-1(Cr). Analysis of the PE products revealed large Ð values, demonstrating that polymerization occurs over a multitude of active Cr centers rather than a singular type of Cr site. Spectroscopic experiments, in the form of powder X-ray diffraction (pXRD), UV/Vis-NIR diffuse reflectance spectroscopy (DRS) and CO probe molecule Fourier transform infrared (FTIR) spectroscopy corroborated these findings, indicating that indeed for each MOF unique active sites are generated, however without alteration of the original oxidation state. Furthermore, the pXRD experiments indicated that one major prerequisite for catalytic activity was the degree of MOF activation by the Et2 AlCl co-catalyst, with the more active materials portraying a larger degree of activation.

A different effect of obesity on ECG in premenopausal and postmenopausal women.

Both obesity and menopause are significant cardiovascular risk factors. In postmenopausal women the protective effect of estrogens is reduced and menopause is frequently associated with occurrence of other significant cardiovascular factors including obesity. This study was focused on evaluating the effect of obesity on the QRS complex in pre- and postmenopausal women. We present results of analysis of 199 electrocardiograms of pre- and postmenopausal women analyzed in relation to the body mass index within normal limits (BMI 20 to 24.9 kg/m2) and obesity (BMI > 30 kg/m2), respectively. Obesity in premenopausal women and menopause significantly affected both the electrical axis (EA) and maximum QRS spatial vector magnitude (QRSmax). The highest QRSmax and electrical axis values were observed in premenopausal lean women, and they were significantly higher as than in the premenopausal obese women, postmenopausal lean and obese women (QRSmax: 1.66 ±â€¯0.4 mV, 1.17 ±â€¯0.35 mV, 1.4 ±â€¯0.46 mV, and 1.35 ±â€¯0.39 mV, resp.). (EA: 56.4 ±â€¯18.0°, 38.22 ±â€¯18.38°, 45.82 ±â€¯18.63°, and 36.75 ±â€¯17.51°). The differences between obese premenopausal women, lean and obese postmenopausal women were not statistically significant. These differences were reflected in 12-lead ECG amplitude. The presence of additional cardiovascular risk factors did not affect the ECG parameters. Obesity significantly affected QRS complex in premenopausal women. This effect was comparable with the effect of menopause. Because all QRS complex changes were within normal limits, these results suggest that ECG evaluation in women should go beyond traditional diagnostic categories and consider the relationship between ECG changes and two cardiovascular risk factors - obesity and menopause.

Addition of Pore-Forming Agents and Their Effect on the Pore Architecture and Catalytic Behavior of Shaped Zeolite-Based Catalyst Bodies.

Porous materials, such as solid catalysts, are used in various chemical reactions in industry to produce chemicals, materials, and fuels. Understanding the interplay between pore architecture and catalytic behavior is of great importance for synthesizing a better industrial-grade catalyst material. In this study, we have investigated the modification of the pore architecture of zeolite-based alumina-bound shaped catalyst bodies via the addition of different starches as pore-forming agents. A combination of microscopy techniques allowed us to visualize the morphological changes induced and make a link between pore architecture, molecular transport, and catalytic performance. As for the catalytic performance in the methanol-to-hydrocarbons (MTH) reaction, pore-forming agents resulted in up to ∼12% higher conversion, an increase of 74% and 77% in yield (14% and 13% compared to 8.6% and 7.7% of the reference sample in absolute yields) toward ethylene and propylene, respectively, and an improved lifetime of the catalyst materials.

Developing Creep and Stress Relaxation Models to Assess the Service Life of an Additive Manufactured Industrial-Scale Recuperator Utilizing Inconel 625 and AISI 310S Materials.

This work is focused on the development of creep and stress relaxation models on Inconel 625 and Stainless Steel 310 materials for additive manufacturing. At the end, the operational lifespan of an industrial-scale additive manufactured recuperator is evaluated. An industrial-scale recuperator for burners with a highly complex geometry is manufactured using Continuous Wave SLM and Pulsed Wave Selective Laser Melting techniques. The recuperator operates under steady but high thermal loads, reaching temperatures of up to 875 °C. Therefore, its service life is assessed, considering creep and stress relaxation phenomena. Two different materials are evaluated: Inconel 625 and Stainless Steel 310. Tensile testing has been conducted on samples at various temperatures to acquire material parameters, incorporating appropriately the anisotropic nature of the materials. Creep parameters were determined through creep experiments and data from the literature, and the recuperator response was simulated by FEA modelling. Analytical creep and stress relaxation models were proposed based on the simulation results for each material to predict their creep response. The service life was determined by applying a custom failure criterion based on the creep testing data. The Inconel 625 recuperator exhibits a service life that is significantly higher compared to any burner's life, while the Stainless Steel 310 recuperator exhibits approximately 27 years of service life. Both materials are considered suitable; however, Inconel 625 offers higher resistance to creep according to creep tests, and due to its lower thermal expansion coefficient, the resulting thermal stresses are lower.

A Ziegler-type spherical cap model reveals early stage ethylene polymerization growth versus catalyst fragmentation relationships.

Polyolefin catalysts are characterized by their hierarchically complex nature, which complicates studies on the interplay between the catalyst and formed polymer phases. Here, the missing link in the morphology gap between planar model systems and industrially relevant spherical catalyst particles is introduced through the use of a spherical cap Ziegler-type catalyst model system for the polymerization of ethylene. More specifically, a moisture-stable LaOCl framework with enhanced imaging contrast has been designed to support the TiCl4 pre-active site, which could mimic the behaviour of the highly hygroscopic and industrially used MgCl2 framework. As a function of polymerization time, the fragmentation behaviour of the LaOCl framework changed from a mixture of the shrinking core (i.e., peeling off small polyethylene fragments at the surface) and continuous bisection (i.e., internal cleavage of the framework) into dominantly a continuous bisection model, which is linked to the evolution of the estimated polyethylene volume and the fraction of crystalline polyethylene formed. The combination of the spherical cap model system and the used advanced micro-spectroscopy toolbox, opens the route for high-throughput screening of catalyst functions with industrially relevant morphologies on the nano-scale.

Visualizing defects and pore connectivity within metal-organic frameworks by X-ray transmission tomography.

Metal-Organic Frameworks (MOFs) have the potential to change the landscape of molecular separations in chemical processes owing to their ability of selectively binding molecules. Their molecular sorting properties generally rely on the micro- and meso-pore structure, as well as on the presence of coordinatively unsaturated sites that interact with the different chemical species present in the feed. In this work, we show a first-of-its-kind tomographic imaging of the crystal morphology of a metal-organic framework by means of transmission X-ray microscopy (TXM), including a detailed data reconstruction and processing approach. Corroboration with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images shows the potential of this strategy for further (non-destructively) assessing the inner architecture of MOF crystals. By doing this, we have unraveled the presence of large voids in the internal structure of a MIL-47(V) crystal, which are typically thought of as rather homogeneous lattices. This challenges the established opinion that hydrothermal syntheses yield relatively defect-free material and sheds further light on the internal morphology of crystals.

Visualizing pore architecture and molecular transport boundaries in catalyst bodies with fluorescent nanoprobes.

The performances of porous materials are closely related to the accessibility and interconnectivity of their porous domains. Visualizing pore architecture and its role on functionality-for example, mass transport-has been a challenge so far, and traditional bulk and often non-visual pore measurements have to suffice in most cases. Here, we present an integrated, facile fluorescence microscopy approach to visualize the pore accessibility and interconnectivity of industrial-grade catalyst bodies, and link it unequivocally with their catalytic performance. Fluorescent nanoprobes of various sizes were imaged and correlated with the molecular transport of fluorescent molecules formed during a separate catalytic reaction. A direct visual relationship between the pore architecture-which depends on the pore sizes and interconnectivity of the material selected-and molecular transport was established. This approach can be applied to other porous materials, and the insight gained may prove useful in the design of more efficient heterogeneous catalysts.

The association of foot structure and footwear fit with disability in children and adolescents with Down syndrome.

BACKGROUND: Foot deformity, flat feet, and the use of ill-fitting footwear are common in children and adolescents with Down syndrome (DS). The aim of this study was to determine whether these observations are associated with foot-specific disability in this group. METHODS: A cross-sectional study design. Foot structure (foot posture determined using the Arch Index, presence of hallux valgus and lesser toe deformities) and footwear fit (determined by length and width percentage differences between the participant's foot and footwear) were assessed in 50 participants with DS (22 females, 28 males) aged five to 18 with a mean (SD) age of 10.6 (3.9) years. Foot-specific disability was determined using the parent-reported Oxford Ankle Foot Questionnaire for Children (OxAFQ-C). Associations between foot structure and footwear fit with the four domains (Physical, School and play, Emotional and Footwear) of the OxAFQ-C were determined using multivariate regression modelling. RESULTS: The mean (SD) Arch Index was 0.29 (0.08), and the prevalence of flat feet, hallux valgus and lesser toe deformities was 76%, 10% and 12% respectively. Few participants wore footwear that was too short (10%), but the use of footwear that was too narrow was common (58%). The presence of hallux valgus was significantly associated with increased disability for the OxAFQ-C School and play domain scores. The use of narrow-fitting footwear was significantly associated with increased levels of disability for the OxAFQ-C Physical, School and play, and Emotional domains. However, these variables only explained between 10% to 14% of the variance in the OxAFQ-C domain scores. There were no significant associations between foot structure and footwear fit with the OxAFQ-C Footwear domain scores. CONCLUSIONS: Flatter feet and lesser toe deformities are not associated with foot-specific disability in children and adolescents with DS. Hallux valgus is associated with foot-specific disability during school and play activities. Ill-fitting footwear (too narrow) is common and is associated with foot-specific disability. Further research is required to identify if the relationship between narrow-fitting footwear and foot-specific disability is causal, and to identify other factors associated with foot-specific disability in children and adolescents with DS.

VOF simulations of the contact angle dynamics during the drop spreading: standard models and a new wetting force model.

INTRODUCTION: In this study,a novel numerical implementation for the adhesion of liquid droplets impacting normally on solid dry surfaces is presented. The advantage of this new approach, compared to the majority of existing models, is that the dynamic contact angle forming during the surface wetting process is not inserted as a boundary condition, but is derived implicitly by the induced fluid flow characteristics (interface shape) and the adhesion physics of the gas-liquid-surface interface (triple line), starting only from the advancing and receding equilibrium contact angles. These angles are required in order to define the wetting properties of liquid phases when interacting with a solid surface. METHODOLOGY: The physical model is implemented as a source term in the momentum equation of a Navier-Stokes CFD flow solver as an "adhesion-like" force which acts at the triple-phase contact line as a result of capillary interactions between the liquid drop and the solid substrate. The numerical simulations capture the liquid-air interface movement by considering the volume of fluid (VOF) method and utilizing an automatic local grid refinement technique in order to increase the accuracy of the predictions at the area of interest, and simultaneously minimize numerical diffusion of the interface. RESULTS: The proposed model is validated against previously reported experimental data of normal impingement of water droplets on dry surfaces at room temperature. A wide range of impact velocities, i.e. Weber numbers from as low as 0.2 up to 117, both for hydrophilic (θadv=10°-70°) and hydrophobic (θadv=105°-120°) surfaces, has been examined. Predictions include in addition to droplet spreading dynamics, the estimation of the dynamic contact angle; the latter is found in reasonable agreement against available experimental measurements. CONCLUSION: It is thus concluded that theimplementation of this model is an effective approach for overcoming the need of a pre-defined dynamic contact angle law, frequently adopted as an approximate boundary condition for such simulations. Clearly, this model is mostly influential during the spreading phase for the cases of low We number impacts (We<˜80) since for high impact velocities, inertia dominates significantly over capillary forces in the initial phase of spreading.

Impact of first metatarsophalangeal joint osteoarthritis on health-related quality of life.

OBJECTIVE: To determine whether there are differences in the foot-specific and general health-related quality of life (HRQOL) of people with and without first metatarsophalangeal (MTP) joint osteoarthritis (OA). METHODS: The foot-specific and general HRQOL of 43 participants (mean ± SD age 50.0 ± 10.8 years) with symptomatic radiographically confirmed first MTP joint OA (case group) was compared to an age-, sex-, and body mass index-matched control group. Foot-specific HRQOL was assessed using the Foot Health Status Questionnaire (FHSQ) and general HRQOL was assessed using the Short Form 36 (SF-36) questionnaire. Both questionnaires are validated instruments with 0-100-point domains. RESULTS: All domains of the FHSQ were significantly lower in the case group (mean ± SD foot pain 55.5 ± 22.3 versus 93.0 ± 7.8, foot function 73.8 ± 20.9 versus 96.9 ± 11.5, footwear 39.1 ± 28.7 versus 76.6 ± 27.0, and general foot health 50.2 ± 27.0 versus 89.7 ± 16.0). Further, the SF-36 physical functioning domain was significantly lower (mean ± SD 82.8 ± 14.7 versus 95.2 ± 6.3) in the case group. CONCLUSION: People with first MTP joint OA experience more foot pain, have greater difficulty performing functional weight-bearing activities, find it more difficult to obtain suitable footwear, and perceive their feet to be in a poorer state of health. Additionally, people with symptomatic first MTP joint OA have greater difficulty performing a broad range of physical tasks and activities.