NLDFT adsorption models for zeolite porosity analysis with particular focus on ultra-microporous zeolites using O2 and H2.

The most often used gases for the PSD characterization of zeolites are N2 and Ar. According to the IUPAC Technical Report (2015), Ar is recommended as more reliable than N2, which molecules possess a significant quadrupole moment that may influence the adsorption isotherms on polar surfaces. In practice, however, using Ar as a cryogen for Ar adsorption measurements is not preferred due to its higher cost than liquid N2. We propose using O2 which has a much lower quadrupole moment than N2, and its adsorption can be measured using standard liquid N2 as a coolant. To support using O2, we demonstrate good agreement between the PSDs calculated from O2 and Ar adsorption. In the present work, we develop several semiempirical models based on nonlocald density functional theory (NLDFT) for the PSD characterization of several types of zeolites. We discuss the underlying difficulties in modeling gas adsorption on zeolites which adsorption potential field depends on both the pore width and the chemical structure of the zeolite. For the analysis of ultra microporous zeolites such as Chabazite and molecular sieve 5A, we apply H2 in combination with O2 at 77 K. H2 molecule has a smaller diameter than O2 and diffuses faster into ultra micropores, reducing the time of isotherm measurement. Moreover, we show that the dual gas analysis method can be used with O2 isotherms measurements omitting low-pressure points, making the analysis faster.

Acute cerebral venous thrombosis - still an underdiagnosed pathology in emergency computed tomography of the brain.

PURPOSE: Acute cerebral venous thrombosis (CVT) is a rare condition that can lead to a serious clinical state; thus, prompt diagnosis and treatment are mandatory. Head computed tomography (CT) plays a crucial role in the initial prompt diagnosis in the emergency setting. The aim of the study was to retrospectively analyse emergency head CT studies and the rate of incorrect diagnoses and main sources of pitfalls. MATERIAL AND METHODS: Retrospective analysis of 31 emergency CT studies (22 without contrast, 19F/12M, age range: 4-94 years) of patients with confirmed acute CVT. RESULTS: Thrombosed dural sinuses were found in 24/31 (77.4%) cases, thrombosed veins in 7/31 (22.6%) cases, no lesions within vessels in 2/31 (6.5%) cases. Haemorrhagic brain lesions were found in 9/31 (29%) cases, hypodense oedema in 6/31 (19.6%) cases, brain swelling in 1/31 (3.2%) cases, and no parenchymal lesions were revealed in 15/31 (48.4%) cases. Correct diagnosis of CVT was established in 15 cases (48.4%); however, it was incorrect in 16 cases (51.6%). Incorrect cases consist of 4 groups: 1 - with both vascular and parenchymal lesions that were overlooked (50%), 2 - with vascular lesions only, which were either overlooked, misinterpreted, or covered by artefacts (31.3%,), 3 - with parenchymal lesions only, which were misinterpreted (12.5%), and 4 - with no lesions present in the emergency head CT (6.2%). CONCLUSIONS: The high rate of incorrect diagnoses of acute CVT based on emergency head CT requires constant training of radiologists and their close cooperation with clinicians because a delayed diagnosis may be lethal to the patient.

Comprehensive Analysis of Hierarchical Porous Carbons Using a Dual-Shape 2D-NLDFT Model with an Adjustable Slit-Cylinder Pore Shape Boundary.

A thorough characterization of the textural properties of hierarchical porous carbons (HPCs) is of utmost importance as it provides information that aids in the selection of a suitable material for a given application and in understanding the phenomena observed once the material becomes part of a system. Gas adsorption-desorption isotherms coupled with the application of density functional theory (DFT) models to these isotherms are common tools for the textural characterization of HPCs, for which pore shape is an essential factor for the determination of pore size distributions (PSDs). By analyzing the experimental adsorption data of a series of CO2-activated HPCs with a progressive development of porosity, it is shown that artifacts are found in the derived PSDs when a slit-cylinder pore shape boundary is fixed at 2 nm, which is the case for the original dual-shape nonlocal DFT (2D-NLDFT-HS) and hybrid quenched solid DFT (QSDFT) models. This study presents a new dual-shape 2D-NLDFT-HS (DS-HS) model that, combined with the 2D-NLDFT-HS model for CO2, provides the possibility of analyzing simultaneously N2 and CO2 adsorption-desorption isotherms and adjusting at the same time the limits for the assumed slit and cylindrical pore shapes. Using the DS-HS approach and adjusting the slit-cylinder boundary at 3 nm allowed eliminating PSDs artifacts. The interactive adjustment of the slit-cylindrical pore shape boundary of the DS-HS model represents a major advantage of this approach allowing for a comprehensive analysis of the adsorption data and a more accurate description of the textural properties of HPC materials.

Alternative view of oxygen reduction on porous carbon electrocatalysts: the substance of complex oxygen-surface interactions.

Electrochemical oxygen reduction reaction (ORR) is an important energy-related process requiring alternative catalysts to expensive platinum-based ones. Although recently some advancements in carbon catalysts have been reported, there is still a lack of understanding which surface features might enhance their efficiency for ORR. Through a detailed study of oxygen adsorption on carbon molecular sieves and using inelastic neutron scattering, we demonstrated here that the extent of oxygen adsorption/interactions with surface is an important parameter affecting ORR. It was found that both the strength of O2 physical adsorption in small pores and its specific interactions with surface ether functionalities in the proximity of pores positively influence the ORR efficiency. We have shown that ultramicropores and hydrophobic surface rich in ether-based groups and/or electrons enhance ORR on carbon electrocatalysts and the performance parameters are similar to those measured on Pt/C with the number of electron transfer equal to 4.

Crystallizing Atomic Xenon in a Flexible MOF to Probe and Understand Its Temperature-Dependent Breathing Behavior and Unusual Gas Adsorption Phenomenon.

Flexible metal-organic frameworks (MOFs) hold great promise as smart materials for specific applications such as gas separation. These materials undergo interesting structural changes in response to guest molecules, which is often associated with unique adsorption behavior not possible for rigid MOFs. Understanding the dynamic behavior of flexible MOFs is crucial yet challenging as it involves weak host-guest interactions and subtle structural transformation not only at the atomic/molecular level but also in a nonsteady state. We report here an in-depth study on the adsorbate- and temperature-dependent adsorption in a flexible MOF by crystallizing atomic gases into its pores. Mn(ina)2 shows an interesting temperature-dependent response toward noble gases. Its nonmonotonic, temperature-dependent adsorption profile results in an uptake maximum at a temperature threshold, a phenomenon that is unusual. Full characterization of Xe-loaded MOF structures is performed by in situ single-crystal and synchrotron X-ray diffraction, IR spectroscopy, and molecular modeling. The X-ray diffraction analysis offers a detailed explanation into the dynamic structural transformation and provides a convincing rationalization of the unique adsorption behavior at the molecular scale. The guest and temperature dependence of the structural breathing gives rise to an intriguing reverse of Xe/Kr adsorption selectivity as a function of temperature. The presented work may provide further understanding of the adsorption behavior of noble gases in flexible MOF structures.

Consistency of carbon nanopore characteristics derived from adsorption of simple gases and 2D-NLDFT models. Advantages of using adsorption isotherms of oxygen (O2) at 77 K.

The pore size distribution (PSD) of porous carbons is most often derived from the analysis of standard N2 and Ar adsorption isotherms measured at 77 and 87 K. From the two gases, Ar is recommended (IUPAC Technical Report 2015) as more reliable for the PSD analysis due to its minimal specific interactions with the surface polar groups. Such interactions may influence the adsorption of N2 molecules due to its significant quadrupole moment. In practice, however, using liquid Ar as a cryogen for Ar adsorption measurements may be challenging because of its high cost and limited availability in various parts of the world. In this study, we propose using O2 adsorption isotherms for the PSD characterization of porous carbons. The quadrupole moment of O2 is less than one-third of the value reported for N2, and thus its susceptibility to specific interactions with polar groups is much smaller than that of N2. We demonstrate a quantitative agreement between the PSD results derived from the adsorption isotherms of O2 and N2 measured at 77 K, and Ar at 87 K on four representative carbon samples. The PSD calculations are performed using adsorption models based on the two-dimensional non-local density functional theory (2D-NLDFT).

2D-NLDFT adsorption models for porous oxides with corrugated cylindrical pores.

In this work, we develop two-dimensional models based on the non-local density functional theory (2D-NLDFT) for the analysis of pore size distribution (PSD) of oxide materials with cylindrical pores with rough and heterogeneous walls. The existing standard NLDFT models for porous oxides assume the smooth energetically uniform surface of the pore walls. Due to this assumption, the calculated theoretical isotherms show typical layering transitions, which are not consistent with the experimental adsorption isotherms measured on real oxide materials. As a result, the fits of standard NLDFT models to N2 or Ar adsorption isotherms show deviations from the experimental points in association with artifacts observed on the calculated PSD plots. The 2D-NLDFT framework allows us to improve the standard model by introducing the corrugation and energetic heterogeneity to the surface of cylindrical pores. The surface roughness and energetic heterogeneity are known characteristics of the oxide surfaces. With these assumptions we develop a comprehensive approach in which both branches of the adsorption isotherm may be used for the PSD analysis of mesoporous oxide materials. We validate this approach by using Ar data measured at 87 K on the reference set of MCM-41 silica samples (Kruk and Jaroniec, 2000). The generated kernels are smooth, do not show layering transitions and fit accurately the reference data.

[Topinambour - nutritional and medical properties of the Jerusalem artichoke (Helianthus tuberoses L.)]. / Topinambur ­ wlasciwosci odzywcze i lecznicze slonecznika bulwiastego (Helianthus tuberosus L.).

Topinambour (Helianthus tuberosus L.), also known as the Jerusalem artichoke is a plant, which origins from North America. In XVII century it was brought to the Europe. For ages it was cultivated due to edible tuber and its healing properties.The aim of the article is to present medical properties and application of topinmbour in patient's diet. Many studies were performed on animals to specify medical properties of topinambour. Results show, that topinambour lowers plasma glucose, total cholesterol and triglyceride levels. It is believed that these effects are caused by high level of inulin present it its tuber.Inulin effect on the human organism was assessed in many clinical studies. It is thought it has prebiotic features, lowers plasma glucose and intestinal pH level, which results in higher calcium bioavailability. Additionaly, it has a positive impact on the plasma lipid profile, acts as an immunomodulator, affecting digestive systems' limfatic tissue. Due to its characteristics, it can be used in the diet of obese and type 2 diabetes mellitus patients.Recently, it was discovered that topinambour tuber secretion works as a cytotoxic agent contra breast cancer cells.

Direct structural evidence of commensurate-to-incommensurate transition of hydrocarbon adsorption in a microporous metal organic framework.

The efficiency of physisorption-based separation of gas-mixtures depends on the selectivity of adsorbent which is directly linked to size, shape, polarizability and other physical properties of adsorbed molecules. Commensurate adsorption is an interesting and important adsorption phenomenon, where the adsorbed amount, location, and orientation of an adsorbate are commensurate with the crystal symmetry of the adsorbent. Understanding this phenomenon is important and beneficial as it can provide vital information about adsorbate-adsorbent interaction and adsorption-desorption mechanism. So far, only sporadic examples of commensurate adsorption have been reported in porous materials such as zeolites and metal organic frameworks (MOFs). In this work we show for the first time direct structural evidence of commensurate-to-incommensurate transition of linear hydrocarbon molecules (C2-C7) in a microporous MOF, by employing a number of analytical techniques including single crystal X-ray diffraction (SCXRD), in situ powder X-ray diffraction coupled with differential scanning calorimetry (PXRD-DSC), gas adsorption and molecular simulations.

Unified method for the total pore volume and pore size distribution of hierarchical zeolites from argon adsorption and mercury intrusion.

A generalized approach to determine the complete distribution of macropores, mesopores, and micropores from argon adsorption and mercury porosimetry is developed and validated for advanced zeolite catalysts with hierarchically structured pore systems in powder and shaped forms. Rather than using a fragmented approach of simple overlays from individual techniques, a unified approach that utilizes a kernel constructed from model isotherms and model intrusion curves is used to calculate the complete pore size distribution and the total pore volume of the material. An added benefit of a single full-range pore size distribution is that the cumulative pore area and the area distribution are also obtained without the need for additional modeling. The resulting complete pore size distribution and the kernel accurately model both the adsorption isotherm and the mercury porosimetry. By bridging the data analysis of two primary characterization tools, this methodology fills an existing gap in the library of familiar methods for porosity assessment in the design of materials with multilevel porosity for novel technological applications.

Toward understanding reactive adsorption of ammonia on Cu-MOF/graphite oxide nanocomposites.

The adsorption of ammonia on HKUST-1 (a metal-organic framework, MOF) and HKUST-1/graphite oxide (GO) composites was investigated in two different experimental conditions. From the isotherms, the isosteric heats of adsorption were calculated from the Clausius-Clapeyron equation following the virial approach. The results on HKUST-1 were compared with those obtained using molecular simulation studies. All materials exhibit higher ammonia adsorption capacities than those reported in the literature. The ammonia adsorption on the composites is higher than that measured separately on the MOF component and on GO. The strong adsorption of ammonia caused by chemical interactions on different adsorption sites is evidenced by the trends in the isosteric heats of adsorption. The molecular simulations conducted on HKUST-1 support the trends observed experimentally. In particular, the strong chemisorption of ammonia on the metallic centers of HKUST-1 is confirmed. Nevertheless, higher adsorption capacities are predicted compared with the experimental results. This discrepancy is mainly assigned to the partial collapse of the MOF structure upon exposure to ammonia, which is not accounted for in the simulation study.

Thermodynamics of CO2 adsorption on functionalized SBA-15 silica. NLDFT analysis of surface energetic heterogeneity.

Siliceous SBA-15 mesoporous molecular sieves were functionalized with different amounts of 3-aminopropyl-trimethoxysilane. To obtain a more detailed insight into the material properties of the prepared samples, their textural parameters were combined with results of thermal analysis. Adsorption isotherms of carbon dioxide on parent and functionalized SBA-15 were measured in the temperature range from 273 to 333 K. From the temperature dependence of CO(2) isotherms the isosteric adsorption heats of CO(2) were determined and discussed. Information about the surface energetic heterogeneity caused by tethered 3-aminopropyl groups were obtained from CO(2) adsorption energy distributions calculated using the theoretical CO(2) adsorption isotherms derived from the non-local density functional theory. The values of isosteric heats and the energy distributions of CO(2) adsorption detect highly energetic sites and enabled quantification of their concentrations.

Tailoring the pore alignment for rapid ion transport in microporous carbons.

The power density and charge-discharge time of electrical double layer capacitors are largely determined by how fast the electrolyte ions can travel within the carbon electrode particles. Our systematic studies using zeolite-templated carbons show that an enhancement in ion transport rate by more than 2 orders of magnitude is possible by minimizing the micropore tortuosity. Very uniform carbon deposition was achieved using a well-controlled process involving the decomposition of acetylene precursor at a reduced pressure of 10 Torr and under a constant flow rate of 100 sccm. Selected carbon samples with well-aligned, straight micropores demonstrate high specific capacitance of up to 300 F/g and outstanding frequency response of up to 10 Hz for 250 microm thick electrodes, indicating an attractive combination of high specific energy and high specific power in electrical double layer capacitors. Such properties are critical for many peak-power hungry applications, such as the leveling of subsecond disturbances in power lines. Our findings provide guidance for the optimal design of porous carbons with greatly improved power storage characteristics.

DFT-based prediction of high-pressure H2 adsorption on porous carbons at ambient temperatures from low-pressure adsorption data measured at 77 K.

Hydrogen adsorption isotherms were measured both at cryogenic temperatures below 1 atm and at ambient temperature at high pressures, up to 90 atm, on selected porous carbons with various pore structures. The nonlocal density functional theory (NLDFT) model was used to calculate the pore size distributions (PSDs) of the carbons, from H2 adsorption isotherms measured at 77 K, and then to predict H2 adsorption on these carbons at 87 and 298 K. An excellent agreement between the predicted and measured data was obtained. Prior to analyzing the porous carbons, the solid-fluid interaction parameters used in the NLDFT model were derived from H2 adsorption data measured at 77 K on nonporous carbon black. The results show that the NLDFT model with appropriate parameters may be a useful tool for optimizing carbon pore structures and designing adsorption systems for hydrogen storage applications.

High-resolution adsorption of nitrogen on mesoporous alumina.

Nitrogen adsorption isotherms on organized mesoporous aluminas prepared by several different synthesis procedures were analyzed by means of comparative plot method using Aluminiumoxid C (Degussa) and alpha-alumina as reference adsorbents. To secure the high-resolution ability of this method, all the adsorption measurements were carefully performed in a relative pressure range from 10(-6) to 0.99. Although some samples of organized mesoporous alumina were treated at temperatures up to 1000 degrees C, only the Aluminiumoxid C has proved to be suitable as a reference adsorbent. The comparative analysis of isotherms on activated aluminas has shown that this method allows the determination of very small amounts of microporosity. The standard nitrogen adsorption data for Aluminiumoxid C and alpha-alumina are presented in a tabulated form, which consists of 91 points for each adsorbent.