Polar Adsorbates Research Articles

Enhanced toluene adsorption over carbon–silica composite with promoted microporosity and moisture resistance

Herein, carbon–silica composite materials were prepared by introducing biomass-derived carbon into the channels of silica gel by concurrent thermal carbonization and chemical etching. With the optimized preparation parameters, a trade-off for the microporosity, carbon contents and toluene adsorption capacity was realized. Moreover, the TEM-EDS spectra evidenced that the carbon generated by chemical activation was homogeneously dispersed in the channels of the silica gel. Notably, when used in toluene adsorption, high adsorption capacity, desorption efficiency and regenerability were simultaneously achieved on the carbon–silica composite sample, along with superb water resistance (up to 80 RH%), as contrasted with the performances of the commercial zeolite adsorbents. Finally, except for the toluene, the composite material demonstrated good adsorption capacity and desorption efficiency for a series of common VOCs species (including acetone, ethyl acetate, n-hexane) as well, but the adsorption towards less polar adsorbates, such as n-hexane and toluene, was more favorable.

In English

Features of interfacial adsorbate/adsorbent phenomena depend on several factors: particulate morphology, texture, and structure of adsorbents, molecular weight, shape, and polarity of adsorbates; as well as prehistory of adsorbents pretreated under different conditions. All these factors could affect the efficiency of practical applications of not only adsorbents but also polymer fillers, carriers, catalysts, etc. Interactions of nonpolar nitrogen, hexane, benzene, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water with individual (silica, alumina), binary (silica/alumina (SA)) and ternary (alumina/silica/titania, AST) nanooxides were studied using experimental and theoretical methods to elucidate the influence of the morphological and textural characteristics and surface composition of the materials on the adsorption phenomena. The specific surface area SX / ratio (X is an adsorbate) changes from 0.7 for hexane adsorbed onto amorphous silica/alumina SA8 with 8 wt. % Al2O3 (degassed at 200 °C) to 1.9 for acetonitrile adsorbed onto pure fumed alumina (treated at 900 °C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of organic molecules interacting with surfaces characterized by certain set and amounts of various active sites, as well as due to changes in the accessibility of pore surface for probe molecules of different sizes. Larger SX / > 1 values are observed for complex fumed oxides with larger primary nanoparticles, greater surface roughness, hydrophilicity, and Brønsted and Lewis acidity of a surface. Both polar and nonpolar adsorbates can change the morphology and texture of aggregates of oxide nanoparticles, e.g., swelling of structures, compacted during various pretreatments, upon the adsorption of liquids. The studied effects should be considered upon practical applications of adsorbents, especially “soft” fumed oxides.

Fly ash-based zeolitic materials of different surface chemistry and texture: Insight into adsorption performance and mechanisms of aqueous BTEX removal

Water contamination caused by anthropogenic, and unforecasted release of BTEX (benzene, toluene, ethylbenzene and xylene) compounds threatens the quality and integrity of aquatic ecosystems. BTEX sorption with novel materials characterized by increased hydrophobicity and stability has been proposed to overcome such contamination. This study aimed to investigate the whole array of hydrothermally synthesized zeolitic materials exhibiting different properties, as well as zeolite/carbon and zeolite/vermiculite composites, to analyse their potential in removing aqueous BTEX. Various parameters and experimental conditions, including the type of volatile organic compounds (VOCs), initial concentration, BTEX coexistence, and increased solution salinity, were studied to verify the applicability of the derived materials. The adsorption capacity of the materials and their governing removal mechanisms were additionally elucidated. The primary removal mechanism involved partitioning on unburned carbon residues, which was observed in zeolite/carbon composites showing the highest BTEX removal efficiency. NaA-zeolite/carbon composite was the most effective in removal of BTEX, with the removal capacity of 15.36 mg/g towards p-xylene. Moreover, the increased salinity of the BTEX solution affects adsorption performance for polar adsorbates, irrespectively of the applied zeolite/carbon composite. Fly-ash (FA) and high-carbon fly-ash (HCFA) were successfully valorised into products with better textural features. These products may effectively tackle organic water pollution caused by VOCs under near-real-life conditions.

Change of the surface and structure of activated carbon as a result of HNO3 modification

In the paper the chemical modification of activated carbon was presented. The activated carbon was modified by nitric acid. For the tested activated carbons, the following physical and chemical properties were determined: bulk density, pH of the water extract, and effective diameter of the grains. Elemental and technical analyses were performed. The pore distribution was determined using mercury porosimetry. Low-temperature nitrogen isotherms were used to analyze the microporous structure. The chemical properties of the surfaces of the tested adsorbents were interpreted by means of the Boehm method. The water vapor adsorption isotherms at 303 K were determined and the adsorption capacity towards methanol was tested using the desiccator method. Thermogravimetric tests were used and, at the same time, the released oxidizing gases from the tested samples were analyzed using a mass spectrometer. As a result of the modification, activated carbon enriched with acidic oxygen functional groups was obtained. The resulting modified activated carbon showed worse structural parameters (when compred to umodified activated carbon), however it was characterized by a higher adsorption capacity in relation to polar adsorbates such as water and methanol, especially in the low pressure range.

Polar Perturbations in Functional Oxide Heterostructures

AbstractGrowth and characterization of metal‐oxide thin films foster successful development of oxide‐material‐integrated thin‐film devices represented by metal‐oxide‐semiconductor field‐effect transistors (MOSFET), drawing enormous technological and scientific interest for several decades. In recent years, functional oxide heterostructures have demonstrated remarkable achievements in modern technologies and provided deeper insights into condensed‐matter physics and materials science owing to their versatile tunability and selective amplification of the functionalities. One of the most critical aspects of their physical properties is the polar perturbation stemming from the ionic framework of an oxide. By engineering and exploiting the structural, electrical, magnetic, and optical characteristics through various routes, numerous perceptive studies have clearly shown how polar perturbations advance functionalities or drive exotic physical phenomena in complex oxide heterostructures. In this review, both intrinsic (engraved by thin‐film heteroepitaxy) and extrinsic (reversibly controllable defect‐mediated disorder and polar adsorbates) elements of polar perturbations, highlighting their abilities for the development of highly tunable functional properties are summarized. Scientifically, the recent approaches of polar perturbations render one to consolidate a prospect of atomic‐level manipulation of polar order in epitaxial oxide thin films. Technologically, this review also offers useful guidelines for rational design to heterogeneously integrated oxide‐based multi‐functional devices with high performances.

Binary fluids in mesoporous materials: Phase separation studied by NMR relaxation and diffusion

Relaxation and diffusion measurements were carried out on single and binary liquids filling the pore space of controlled porous glass Vycor with an average pore size of about 4 nm. The dispersion of the longitudinal relaxation time T1 is discussed as a means to identify liquid-surface interaction based on existing models developed for metal-free glass surfaces. In addition, the change of T1 and T2 with respect to their bulk values is discussed, in particular T2 serves as a probe for the strength of molecular interactions. As the native glass surface is polar and contains a large amount of hydroxyl groups, a pronounced interaction of polar and protic adsorbate liquids is expected; however, the T1 dispersion, and the corresponding reduction of T2, are also observed for non-polar liquids such as alkanes and cyclohexane. Deuterated liquids are employed for simplifying data analysis in binary systems, but also for separating the respective contributions of intra- and intermolecular interactions to the overall relaxation rate. Despite the lack of paramagnetic impurities in the glass material, 1H and 2H relaxation dispersions of equivalent molecules are frequently found to differ from each other, suggesting intermolecular relaxation mechanisms for the 1H nuclei. The variation of the T1 dispersion when comparing single and binary systems gives clear evidence for the preferential adsorption of one of the two liquids, suggesting complete phase separation in several cases. Measurement of the apparent tortuosity by self-diffusion experiments supports the concept of a local variation of sample composition within the porespace.

Adsorption of naphthalene and its derivatives onto high-density polyethylene microplastic: Computational, isotherm, thermodynamic, and kinetic study

Microplastics (MP) have received great attention due to the mass-produced residues discharged into the environment. MP are ideal for adhering to organic pollutants that can be easily dispersed, thus posing risks to human health. Furthermore, little has been reported on how different functional groups in polycyclic aromatic hydrocarbons (PAH) derivatives influence the adsorption behavior on MP. To better understand this process, groups methyl (–CH3) and hydroxyl (–OH) were selected and commercial and waste high-density polyethylene (HDPE, ≤ 1 mm) were used as adsorbents, and Naphthalene (Nap), 1-Methyl-Naphthalene (Me-Nap) and α-Naphthol as adsorbates. The results showed different behaviors for nonpolar and polar adsorbates. Dispersion forces were the main type of interaction between HDPE and Nap/Me-Nap, while dipole-induced dipole forces and H-bonding were the chief interactions involving MP and polar compounds. Regardless the HDPE source, Nap and Me-Nap have a Type III isotherm, and α-Naphthol presents a Type II isotherm. Nap and Me-Nap fitted to Freundlich isotherm of an unfavorable process (n = 2.12 and 1.11; 1.87 and 1.31, respectively), with positive values of ΔH° (50 and 77.17; 66 and 64.63 kJ mol−1) and ΔS° (0.070 and 0.0145; 0.122 and 0.103 kJ mol−1) for commercial and waste MP, respectively. Besides, the adsorption isotherm of α-Naphthol on commercial and waste HDPE fitted to the Langmuir model (Qmax = 42.5 and 27.2 μmol g−1, respectively), presenting negative values of ΔH° (−43.71 and −44.10 kJ mol−1) and ΔS° (−0.037 and −0.025 kJ mol−1). The adsorption kinetic study presents a nonlinear pseudo-second-order model for all cases. The K2 values follow the order Me-Nap > Nap >α-Naphthol in both MP. Therefore, this experimental study provides new insights into the affinity of PAH derivatives for a specific class of MP, helping to understand the environmental fate of residual MP and organic pollutants.

Insights and Heuristics for Predicting Diffusion Rates of Chemical Warfare Agents in Zirconium Metal-Organic Frameworks.

Designing nanoporous catalysts to destroy chemical warfare agents (CWAs) and environmental contaminants requires consideration of both intrinsic catalytic activity and the mass transfer of molecules in and out of the pores. Polar adsorbates such as CWAs experience a heterogeneous environment in many metal-organic frameworks (MOFs) due to the arrangement of the metal nodes and organic linkers of the MOF. However, quantitative relationships between the pore architecture and the resulting diffusion properties of polar molecules have not been established. We used molecular dynamics simulations to calculate the diffusion coefficients of the CWA simulant dimethyl methyl phosphonate (DMMP) in a diverse set of 776 MOFs with Zr6 nodes. We developed a 4-parameter machine learning model to predict DMMP diffusivities in Zr6 MOFs and found the model to be transferable to the CWA sarin. We then developed a simplified heuristic based on the machine learning model that the node-node distance and accessible surface area should be maximized to find MOFs with rapid CWA diffusion.

Thermal desorption characteristics of the adsorbate in activated carbon based on a two-dimensional heat and mass transfer model

• A multiphase model of heat and mass transfer in porous media is established. • The multiphase model is validated to simulate the thermal desorption behavior of activated carbon adsorption. • A simplified evaporation rate formula is proposed, and the agreement between the model and the experimental results are verified. • The effect of high thermal conductivity activated carbon on thermal regeneration time is analyzed. • The effects of polar and non-polar adsorbates on model accuracy are analyzed. Thermal desorption of adsorbate in activated carbon is the main part in the thermal regeneration process of spent activated carbon, and previous studies have carried out a series of numerical simulations on it. However, since activated carbon is a porous medium, the heat and mass transfer in activated carbon is different from that in solid. In this paper, a multiphase model of heat and mass transfer in porous media was constructed to study the thermal desorption characteristics of adsorbate in spent activated carbon. In addition, a simplified evaporation rate formula is proposed in this paper, and the agreement between the simulation and the experimental results is verified. When the surroundingtemperature is less than 673.15 K, increasing the surrounding temperature has a significant effect on reducing the thermal desorption time of the adsorbate. Using activated carbon with a thermal conductivity of 5 W / m ∙ K can save about 40% of energy consumption. The model established in this paper can accurately simulate the thermal desorption of adsorbate in activated carbon, which is helpful to deeply understand the mechanism of activated carbon thermal regeneration. In engineering practice, the model can provide technical support for optimizing the thermal regeneration process of spent activated carbon and reducing energy consumption in a targeted manner.

In English

Interfacial phenomena at a surface of porous and highly disperse adsorbents in the systems containing strongly and weakly bound and unbound liquids depend strongly on the confined space effects. These effects as well as the temperature behavior of liquids located in pores or voids between nanoparticles depend on many factors. They are the pore size distributions, pore volume, specific surface area, surface chemistry of adsorbents, chemical structure and molecular sizes of adsorbates, accessibility of pores vs. probe molecule sizes, as well as textural instability of adsorbents. This instability can appear, e.g., as compaction of fumed oxides under action of liquid adsorbates, especially water, or due to mechanochemical activation. The aim of this study is to analyze features of the interfacial phenomena upon interactions of fumed oxides (silica, alumina, alumina/silica/titania) and porous silicas (silica gels and precipitated silica) with polar (water, dimethyl sulfoxide), weakly polar (chloroform), and nonpolar (n-decane, aromatic benzene and toluene) liquid adsorbates depending on the morphological and textural characteristics of the adsorbents, various adsorbate characteristics, and temperature. The observed effects as well as related phenomena are important because they can differently influence the efficiency of practical applications of adsorbents under various conditions (temperature, pressure, concentrations) depending on the characteristics of adsorbents and adsorbates (liquids, solvents and solutes).

Purge gas humidity improves microwave-assisted regeneration of polymeric and zeolite adsorbents

Microwave (MW) heating can be an effective method for adsorbent regeneration; however, it is limited to adsorbents with high MW absorption ability. In this study, two low MW absorption adsorbents (a beta type zeolite and a hyper-crosslinked polystyrene resin) were regenerated using MW heating to study the effect of purge gas humidity on MW absorption. Water saturation of the purge gas used during MW heating enhanced MW absorption by the adsorbent bed. The zeolite, a hydrophilic adsorbent, showed higher interaction with water molecules in the MW field than the resin, a hydrophobic adsorbent. The interaction of water molecules with the adsorbent surface and the water vapor concentration in the purge gas were found to be the main factors governing the extent of MW heating in the studied adsorbents. MW heating using both dry and humid purge gases was utilized to desorb model polar and non-polar adsorbates (isopropanol and cyclohexane) from the adsorbents. Using water-saturated purge gas reduced the MW energy needed for the complete desorption of cyclohexane and isopropanol on the zeolite by 73 % and 61 %, respectively, and on the resin by 33 % and 25 %, respectively. Nitrogen adsorption analysis showed that BET surface area and total pore volume of adsorbents before and after MW-assisted regeneration were comparable. This study shows that using water-saturated purge gas enhances the MW regeneration of adsorbents with poor dielectric properties.

Determination of activated carbon fiber adsorption capacity for several common organic vapors: applications for respiratory protection

ABSTRACT In the context of workplace safety, activated carbon in the fiber form (i.e., activated carbon fiber, ACF) represents an alternative adsorbent to granular activated carbon (GAC) for use in organic vapor respiratory protection devices. ACFs are high surface area carbonaceous materials that are often available in a self-supporting non-woven form. The physical form of ACF suggests the potential for a filtration medium that is capable of supporting both organic vapor adsorption and particulate filtration. To study the application of these materials in respiratory protection devices, ACFs (ACFF 1200 m2/g, ACFF 1800 m2/g, and ACFF 2000 m2/g) were challenged with representative organic vapors (toluene, hexane, and methyl ethyl ketone (MEK)) at an occupationally relevant concentration (200 ppm). Breakthrough curves were generated for at least three different bed weights of adsorbent. Pressure drop (i.e., the resistance across the filtration media) was also measured to determine maximum ACF bed depths for use in respiratory protection devices. Breakthrough experiments indicate that ACFF 2000 has the highest adsorption capacity for toluene (381 mg/g), followed by ACFF 1800 and ACFF 1200 (344 mg/g and 239 mg/g, respectively). A similar trend was observed for hexane: 221 mg/g, 196 mg/g, and 146 mg/g for ACFF 2000, ACFF 1800, and ACFF 1200, respectively. ACFF 1200 showed the highest adsorption capacity for the polar adsorbate MEK (168 mg/g), followed by ACFF 1800 and ACFF 2000 (166 mg/g and 147 mg/g, respectively). Based on the constraints of pressure drop, it seems unlikely the exclusive use of ACF in a filtering facepiece respirator can provide an adsorbent mass sufficient for full shift protection against organic vapor contaminants at or above the legally enforceable permissible exposure level (PEL). Nevertheless, the incorporation of ACF into a facepiece respirator appears promising for “nuisance odor” applications; i.e., the further reduction of organic vapor concentrations when workplace exposures are already below PEL concentrations. Implications: This research brings innovation to the field of occupational health and air pollution control technology by investigating the adsorption performance of activated carbon fiber (ACF) media in the context of worker respiratory protection. ACF properties such as high specific surface area (m2/g), high permeability to airflow, and rapid adsorption kinetics make it ideal for use in thin, N95-style respirators for organic vapors. Respiratory protection is an exciting and relevant application for ACF media. A lightweight adsorbent such as ACF, if incorporated into an N95-style respirator, could potentially provide nuisance-level VOC protection in a physical form that is accessible to workers and consistent with OSHA’s voluntary use provisions for facepiece respirators. The research presented in this manuscript represents one of several steps planned in the characterization of ACF media for this particular application.

Influence of physical structures and chemical modification on VOCs adsorption characteristics of molecular sieves

The adsorption method using molecular sieves as adsorbent is one of the effective ways to control the emission of volatile organic compounds (VOCs), while the unclear adsorption mechanism between different molecular sieves and VOCs blocks its industrial application. The effects of physical structure and chemical modification of molecular sieves on the adsorption of VOCs were studied by computer simulation and adsorption experiment. Grand Classical Monte Carlo (GCMC) simulation was employed to investigate the adsorption behaviors of VOCs in a variety of pure silica molecular sieves with different physical structures, including aldehydes, ketones and benzenes. Further, combined with density functional theory (DFT) calculations, the influences of chemical modification on the adsorption of VOCs were investigated. Finally, the theoretical results were verified through adsorption experiments. The results revealed that the molecular sieve topology, the pore diameter of the molecular sieve, and the molecular kinetic diameters of VOCs all markedly influenced the adsorption of VOCs. Pure silica molecular sieves exhibited considerable adsorption ability for polar adsorbates. For nonpolar adsorbates, the adsorption ability decreased as the molecular volume increased. The DFT results indicated that the adsorption of VOCs is stronger at Cu2+ site than [Cu-OH]+ site in modified MFI. The experimental results of toluene adsorption for MFI, BEA, and Y-type zeolites strongly supported the theoretical results.

Induced Active Sites by Adsorbate in Zeotype Materials.

There has been a long debate on how and where active sites are created for molecular adsorption and catalysis in zeolites, which underpin many important industrial applications. It is well accepted that Lewis acidic sites (LASs) and basic sites (LBSs) as active sites in pristine zeolites are generally believed to be the extra-framework Al species and residue anion (OH-) species formed at fixed crystallographic positions after their synthesis. However, the dynamic interactions of adsorbates/reactants with pristine zeotype materials to "create" sites during real conditions remain largely unexplored. Herein, direct experimental observation of the establishment of induced active sites in silicoaluminophosphate (SAPO) by an adsorbate is for the first time made, which contradicts the traditional view of the fixed active sites in zeotype materials. Evidence shows that an induced frustrated Lewis pair (FLP, three-coordinated framework Al as LAS and SiO (H) as LBS) can be transiently favored for heterolytic molecular binding/reactions of competitive polar adsorbates due to their ineffective orbital overlap in the rigid framework. High-resolution magic-angle-spinning solid-state NMR, synchrotron X-ray diffraction, neutron powder diffraction, in situ diffuse reflectance infrared Fourier transform spectroscopy, and ab initio molecular dynamics demonstrate the transformation of a typical Brønsted acid site (Al(OH)Si) in SAPO zeolites to new induced FLP structure for hetereolytic binding upon adsorption of a strong polar adsorbate. Our unprecedented finding opens up a new avenue to understanding the dynamic establishment of active sites for adsorption or chemical reactions under molecular bombardment of zeolitic structures.

Effects of external electric field on the sensing property of volatile organic compounds over Janus MoSSe monolayer: a first-principles investigation.

Janus 2D transition metal dichalcogenide (TMD) is a new generation 2D material with a unique asymmetric structure. This asymmetric structure (or out-off plane symmetric geometry) of Janus 2D TMD has been reported to yield tunable electronic properties through strain and electric field, which can also be applied in gas sensing. In this work, we performed DFT calculations to investigate the gas sensing property of cyclohexane and acetone on MoS2 and Janus MoSSe monolayers under external electric fields. Our results show that cyclohexane possesses slightly larger adsorption energy on pristine MoS2 and Janus MoSSe monolayers than acetone without external electric fields. After applying the external electric fields, the adsorption energy for cyclohexane on MoS2 shows no enhancement. However, the adsorption energy of acetone shows the most substantial enhancement on the Janus MoSSe monolayer. We found that the dipole moment orientations of adsorbates and the monolayer can strongly interact with the external electric fields. Hence, the combination of polar adsorbate and polar material, i.e., acetone and Janus MoSSe, demonstrates the most vital sensitivity under the applied bias. On the other hand, the non-polar adsorbate and non-polar material combination show a negligible effect on external bias. These findings can be applied to the design of gas sensors in the future through polar materials.

In English

The aim of this review paper was to analyze investigation results on interfacial and temperature behaviors of nonpolar and polar adsorbates interacting with individual and complex fumed metal or metalloid oxides (FMO), initial and subjected to various treatments or chemical functionalization and compared to such porous adsorbents as silica gels, precipitated silica, mesoporous ordered silicas, and polymeric composites. Note that the particulate morphology of FMO depends strongly not only the flame reaction conditions but also on the types and amounts of reagents, as well their distribution in the flame. Therefore, complex nanooxides can include core-shell nanoparticles, (CSNP) of 50-200 nm in size with titania or alumina cores and silica or alumina shells in contrast to simple and smaller nanoparticles of individual FMO. CSNP could be destroyed under high-pressure cryogelation (HPCG) or mechanochemical activation (MCA). These treatments as well simple hydrocompaction (controlled wetting-drying) affect the structure of aggregates of nanoparticles and agglomerates of aggregates, resulting in their becoming more compacted. The analysis shows that complex FMO could be more sensitive to external actions than simple nanooxides such as fumed silica. Any treatment of ‘soft’ FMO affects the interfacial and temperature behaviors of polar and nonpolar adsorbates. Rearrangement of secondary particles and surface functionalization affect the freezing-melting point depression of adsorbates. For some adsorbates, open hysteresis loops became readily apparent in adsorption-desorption isotherms. Clustering of adsorbates bound in pores causes reduced changes in enthalpy during phase transitions (freezing, fusion). Freezing point depression and melting point elevation cause significant hysteresis freezing-melting effects for adsorbates bound to initial and treated FMO in textural pores (voids between nanoparticles in secondary structures). Relaxation phenomena for both low- and high-molecular weight adsorbates or of filled polymeric composites are affected by the morphology of primary particles, structural organization of secondary particles of differently treated or functionalized FMO, content of adsorbates, co-adsorption order, and temperature.

In English

The aim of this study was to analyze various theoretical models (clusters, systems with periodic boundary conditions) and methods, which could be applied to investigate the adsorption phenomena and for better interpretation of the experimental data. The density functional theory (DFT) and semiempirical (PM7) methods were used to model the adsorption phenomena at a surface of fumed nanooxides, silica gels, activated carbons, etc. The main idea is that appropriate theoretical analysis allows a deeper insight into interfacial phenomena related to the structure & properties of the adsorption layers vs. the textural and other characteristics of adsorbents. Comparison of the theoretically calculated characteristics with experimental ones can allow more accurate interpretation of the effects observed in various experiments on the adsorption phenomena. It was established that polarization of nonpolar and polar molecules adsorbed onto a polar surface and charge (& proton) transfer play an important role, as well as confined space effects. It enhances the interaction energy of adsorbed molecules bound to a solid surface and affects the surface orientation of adsorbed molecules, as well the behavior of the adsorption layer vs. temperature, pressure or concentration, as well other conditions. Surface hydrophobization reduces the interaction energy for both polar and nonpolar adsorbates. Adsorbates clusterization reduces the average energy of interaction of the adsorption layer with a surface per a molecule. The charge transfer is observed for both polar and nonpolar molecules interacting with polar surface functionalities. The mostly strong interfacial effects changing the behavior of the adsorption layer are observed upon proton transfer to the adsorbed molecules or vice versa. Variation in orientation of adsorbed molecules results in overestimation of the specific surface area estimated using a fixed value of surface area occupied by a probe molecule (e.g. 0.162 nm 2 for N 2 ).

Cluster-induced desorption investigated by means of molecular dynamics simulations-Microsolvation in clusters of polar and non-polar constituents.

The desorption of surface-adsorbed molecules induced by cluster-surface collisions of neutral molecular clusters, in particular, SO2 clusters, was investigated by means of molecular dynamics simulations. The desorption efficiency was found to be in general much higher for clusters of polar molecules when compared to nonpolar cluster constituents, for both nonpolar and polar adsorbates. In all cases, desorption is shown to proceed via dissolvation of the analyte in the cluster. In systems with nonpolar cluster constituents, the process is mainly driven by the increase in the entropy of the dissolved analyte in a larger cluster fragment. The latter process is enhanced by polar cluster constituents since the respective clusters show lower fragmentation at comparable kinetic energy and thus provide in average larger cluster fragments for the analytes to be dissolved in. In systems with clusters of polar constituents and polar adsorbates, the process is most efficient due to the additional energetic stabilization of the desorbed molecule in the solvation shell formed in the cluster fragment.

Cobalt Incorporated Porous Aromatic Framework for CO2/CH4 Separation

Natural gas decarburization is an important issue as CO2 reduces its energy density and corrodes equipment with humidity. Here, we used PAF-1 as pours platform and derived PAF-1-SO3Co as an efficient and stable CO2/CH4 separation material by introducing cobalt sulfonate groups. Particularly, transition metal cobalt owns rich d-electron orbit and interacts with polar molecules evidently, which is suitable for improving the interaction between polar adsorbate and adsorbent. The experiment results further demonstrate this rule and show that the selectivity of PAF-1-SO3Co reaches 14.27 at 298 K and 1 bar, which has increased almost 5 times than PAF-1. Importantly, PAF-1-SO3Co exhibits remarkably high regenerability (75%) and sorbent selection parameter (S, 85.8). Moreover, PAF-1-SO3Co has dramatically high working stability, whose adsorption performance shows ignorable decrease after soaking in simulated acidic environment even for 1 week. Accordingly, PAF-1-SO3Co is a promising adsorbent for separation and p...

New Model for Predicting Adsorption of Polar Molecules in Metal-Organic Frameworks with Unsaturated Metal Sites.

Conventional molecular models fail to correctly describe interactions of adsorbates with coordinatively unsaturated sites (CUS) present in a large number of metal-organic frameworks (MOFs). Here, we confirm the failure of these models for a prototypical polar adsorbate, carbon monoxide, and show that simply adjusting their parameters leads to poor agreement with experimental isotherms when outside the fitting conditions. We propose a new approach that combines quantum mechanical density functional theory (DFT) with Monte Carlo simulations to rigorously account for specific interactions at the CUS. By explicitly including electrostatic interactions and employing accurate DFT functionals that describe dispersion interactions, our modeling approach becomes generally applicable to both polar and nonpolar molecules. We demonstrate that this CUS model leads to substantial improvement in carbon monoxide adsorption isotherm predictions, and correctly captures the coordination binding mechanism. This paper represents a major stepping stone in the development of a robust, transferable and generally applicable approach to describe the complex interactions between gas molecules and CUS, with great potential for use in large-scale screening studies.