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Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the separation of azeotropic refrigerants remains challenging, such as typical mixtures of CH2F2 (HFC-23) and CHF3 (HFC-32), due to a lack of adsorptive mechanisms. Metal–organic frameworks (MOFs) can provide a promising solution for the separation of CHF3–CH2F2 mixtures. In this study, the adsorption mechanism of CHF3–CH2F2 mixtures in TIFSIX-2-Cu-i was revealed at the microscopic level by combining static pure-component adsorption experiments, molecular simulations, and density-functional theory (DFT) calculations. The adsorption separation selectivity of CH2F2/CHF3 in TIFSIX-2-Cu-i is 3.17 at 3 bar under 308 K. The existence of similar TiF62− binding sites for CH2F2 or CHF3 was revealed in TIFSIX-2-Cu-i. Interactions between the fluorine atom of the framework and the hydrogen atom of the guest molecule were found to be responsible for determining the high adsorption separation selectivity of CH2F2/CHF3. This exploration is important for the design of highly selective adsorbents for the separation of azeotropic refrigerants. [ABSTRACT FROM AUTHOR]

Oil-water mixture separation technology is viewed as a promising solution to offshore oil spill. Among the current technologies, solar-driven crude oil adsorption, based on interface photothermal conversion effects, has piqued enormous interest due to its low energy consumption and high efficiency. In this work, the recent progress on photothermal materials for crude oil adsorption is reviewed. First, an overview of interface photothermal conversion effect is presented. Then, recent efforts in photothermal adsorbents focusing on their structure design are summarized. Finally, the challenges and opportunities of photothermal devices for crude oil adsorption are elaborated. [ABSTRACT FROM AUTHOR]

Reverse osmosis and nanofiltration (NF) are the essential physical separation technologies used to remove contaminants from liquid streams. A hybrid of nanofiltration and forward osmosis (FO) was used to increase the removal efficiency of heavy metals in synthesized oil effluents. Thin-film nanocomposite (TFN) membranes were synthesized by applying surface polymerization on a polysulfone substrate to use in the forward osmosis process. The impact of different membrane fabrication conditions such as time, temperature, and pressure on effluent flux, the effect of different concentrations of the heavy metal solution on adsorption rate and sedimentation rate, the impact of TiO2 nanoparticles on the performance and structure of forward osmosis membranes were investigated. The morphology, composition, and properties of TiO2 nanocomposites made by the infrared spectrometer and X-ray diffraction (XRD) were studied. Kinetic modeling and Langmuir, Freundlich, and Tamkin relationships were used to draw adsorption isotherms and evaluate adsorption equilibrium data. The results indicated that pressure and temperature directly affect water outlet flux, and time affects it indirectly. Evaluating the isothermal relationships revealed that chromium adsorption from the TFN 0.05 ppm membrane and thin-film composite (TFC) membrane follows the Langmuir model with correlation coefficients of 0.996 and 0.995, respectively. The significant removal of heavy metals and the acceptable amount of water flux demonstrated the appropriate potential of the titanium oxide nanocomposite membrane, which can be used as an effective adsorbent to remove chromium from aqueous solutions. [ABSTRACT FROM AUTHOR]

Since its first industrial production in 1890s, acetylene has played a vital role in manufacturing a wide spectrum of materials. Although current methods and infrastructures for various segments of acetylene industries are well‐established, with emerging functional porous materials that enabled desired selectivity toward target molecules, it is of timely interest to develop new efficient technologies to promote safer acetylene processes with a higher energy efficiency and lower carbon footprint. In this Minireview, we, from the perspective of materials chemistry, review state‐of‐the‐art examples of advanced porous materials, namely metal–organic frameworks and decorated zeolites, that have been applied to the purification and storage of acetylene. We also discuss the challenges on the roadmap of translational research in the development of new solid sorbent‐based separation technologies and highlight areas which require future research efforts. [ABSTRACT FROM AUTHOR]

This review highlights the advantages of incorporating hexagonal Boron Nitride (BN) into the current membrane-based architectures for water remediation over other well-explored 2D nanomaterials such as graphene, graphene oxide, molybdenum sulphide, MXenes. BN has an interlayer spacing of 3.3A0 which is similar to that of graphene, but smaller than that of the other 2D nanomaterials. BN is bioinert, and stable under harsh chemical and thermal conditions. When combined with thin film composite and mixed matrix membrane architectures, BN can help achieve high permeance, dye rejection, and desalination. Laminar membranes assembled by BN nanosheets do not swell uncontrollably in aqueous environments unlike graphene oxide. BN nanomaterials have a large specific surface area which implies more adsorption sites, and are inherently hydrophobic in nature, which means the adsorbent in its powder form can be easily separated from contaminated water. BN adsorbents can be regenerated by treating with chemicals or heating to high temperatures to remove the adsorbate, without damaging the BN, due to its thermal and chemical inertness. BN nanomaterials have the potential to circumvent the current shortcomings of membranes and adsorbents, while greatly enhancing the performance of membranes and adsorbents for water remediation. [ABSTRACT FROM AUTHOR]

The adsorption efficiency of synthetic NaX and NaA zeolites used in integrated purification units of low-temperature Xe-containing mixture separation plants was studied. The Kr adsorption capacity of the zeolites was estimated from the experimental data on filling of Kr adsorbers as a part of the technological adsorber preparation process and the Xe adsorption capacity of the adsorbents was estimated from the data on Xe replacement from the purification unit. The experimentally obtained isotherms of N2, Xe, and CO2 adsorption on NaA zeolite are compared with the published data. The obtained data may be useful for planning routine and research work on high-purity Kr and Xe production plants. [ABSTRACT FROM AUTHOR]

Adsorption is an important technology for the separation of different tea components. The adsorption behavior of L-theanine onto adsorbents was comprehensively studied in this paper. Among tested adsorbents, cation exchange resin ZGSPC106Na and D001SD were suitable for separating L-theanine, PVPP and PA-6 for catechins and macroporous resin HPD-400 for caffeine. Adsorption of L-theanine onto the cation resins was significantly influenced by the acidity, contact time and temperature. The adsorption behavior could be described by the pseudo-second-order rate equation and fitted to Langmuir and Freundlich models. ZGSPC106Na exhibited higher adsorption capacity, while D001SD showed higher adsorption selectivity. These might be attributed to the distinctive structure of the two resins and different ionization of the adsorbates. A method for simultaneous preparation of decaffeinated polyphenols, caffeine-enriched extract and decaffeinated L-theanine was established through successive separation on the columns fulfilled with PA-6, HPD-400 and D001SD, respectively. [ABSTRACT FROM AUTHOR]

Single crystals of 2D coordination network {Cu2L2 ⋅ (DMF)3(H2O)3}n (1‐DMF) were prepared by reaction of commercial reagents 3‐formyl‐4‐hydroxybenzoic acid (H2L) and Cu(NO3)2 in dimethylformamide (DMF). The single‐crystal structure shows two distinct Cu(II) coordination environments arising from the separate coordination of Cu(II) cations to the carboxylate and salicylaldehydato moieties on the linker, with 1D channels running through the structure. Flexibility is exhibited on solvent exchange with ethanol and tetrahydrofuran, while porosity and the unique overall connectivity of the structure are retained. The activated material exhibits type I gas sorption behaviour and a BET surface area of 950 m2 g−1 (N2, 77 K). Notably, the framework adsorbs negligible quantities of CH4 compared with CO2 and the C2Hn hydrocarbons. It exhibits exceptional selectivity for C2H2/CH4 and C2H2/C2Hn, which has applicability in separation technologies for the isolation of C2H2. [ABSTRACT FROM AUTHOR]

The separation and purification of xylene isomers is an industrially important but challenging process. Developing highly efficient adsorbents is crucial for the implementation of simulated moving bed technology for industrial separation of these isomers. Herein, we report a stacked one-dimensional coordination polymer {[Mn(dhbq)(H2O)2], H2dhbq = 2,5-dihydroxy-1,4-benzoquinone} that exhibits an ideal molecular recognition and sieving of xylene isomers. Its distinct temperature-adsorbate-dependent adsorption behavior enables full separation of p-, m-, and o-xylene isomers in both vapor and liquid phases. The delicate stimuli-responsive swelling of the structure imparts this porous material with exceptionally high flexibility and stability, well-balanced adsorption capacity, high selectivity, and fast kinetics at conditions mimicking industrial settings. This study may offer an alternative approach for energy-efficient and adsorption-based industrial xylene separation and purification processes. [ABSTRACT FROM AUTHOR]

Green synthesis of bentonite-iron nanoparticles (Be-FeNPs) has been carried out using the leaf extract of Helicteres isora and its antibacterial and adsorption capacity for the removal of Methyl Blue (MB) dye have been also studied. The prepared Be-FeNPs and iron nanoparticles (FeNPs) are characterized by UV-visible, FTIR spectroscopic techniques and SEM analysis. The antibacterial activity of Be-FeNPs show good zone of inhibition against E.coli and S.aureus. Further the prepared composite (Be-FeNPs) and bentonite are used as adsorbents for the removal of Methyl Blue (MB) dye in aqueous solution under various experiment parameters like initial concentration, contact time and pH. The optimum initial pH, adsorbent concentration and time were determined to be 8.1, 45°C, and 100 ppm, 80 min for MB adsorption on to Be-FeNPs. The experimental data for MB adsorption fits well to the Freundlich and Langmuir isotherm models. The kinetic equations like Natarajan-Khalaf, Bhattacharya-Venkobachar and Lagergren equations were found to be applicable. The surface morphology of the Be-FeNPs before and after adsorption of dye revealed that it can be used as an excellent adsorbent for dye removal from dilute industrial effluents. [ABSTRACT FROM AUTHOR]

Nowadays, sustaining the atmosphere and protecting it from global warming are recognized as the main concerns of the planet. This problem has been addressed through the development of a number of different carbon capture and sequestration approaches. Lately, metal‐organic framework (MOF) has emerged as the most auspicious CO2 adsorption and conversion material. This novel class of porous material has demonstrated tremendous potential for gas separation technologies, particularly CO2 adsorption and conversion due to their remarkable characteristics. Therefore, the present review attempted to provide current understanding of the CO2 adsorption and conversion performance over MOF‐based materials. This review paper discussed the type and properties of the MOF, effect of metal and ligand on MOF's properties, and various applications of MOF. Furthermore, future insights were proposed for better design and development of MOF‐based materials for CO2 applications. [ABSTRACT FROM AUTHOR]

Chromatography is one of the most popular methods for the separation of compounds in modern pharmaceutical industry and science. Despite the extensive use of the reversed phase chromatography in analytical and preparative applications, the normal phase adsorption chromatography has a special place in purifying post-reaction mixtures or the separation of natural extracts, especially in wet load mode, because of simplicity and high velocity of preparation. Complex mixtures, more difficult to separate, require gradient methods to obtain better results of separations. These methods can be developed by external software, but the automatic methods are often not very accurate and the negative impact of wet load application on separation quality is considerable in them. Therefore, we present the thin-layer chromatography (TLC) gradient optimization strategy for wet load separations to obtain repeatable results of separations for different compounds without worrying about negative impact of wet loading on separation quality. The strategy provides information about an elution model of desired compound, which is used to develop the gradient method. The strategy also allows to standardize the separation length, because gradient methods performed by the TLC gradient optimization strategy have a very similar duration time in column volumes. The method can also be simply scaled because of using the column volume as a base unit in calculations. [ABSTRACT FROM AUTHOR]

Water bodies polluted with toxic dyes have been treated using various separation techniques. Biosorption as a process of adsorption onto biological materials including living and dead is of more consideration recently for pollutant removal. Fungal biosorbents have a great potential in dye removal due to varied functional groups, eco-friendly, cost-effective nature and a continuously used for application from food and industrial fermentation operations. This article discusses the health risk caused by dyes, presents the biosorptive ability of various fungi in dye removal from aqueous solution, reviews the different physico-chemical factors influencing adsorption, kinetic and equilibrium adsorption data and possible mechanisms in the adsorption process. [ABSTRACT FROM AUTHOR]

Simulated moving bed (SMB) adsorption has potential for efficient separation of many valuable chemical mixtures, but considerably less attention has been devoted to multicomponent feeds relative to binary mixtures. We take a rigorous experimental and modeling approach to study multicomponent separation of aromatics and aliphatics with a mesoporous silica adsorbent, which is relevant in many petrochemical applications such as separation of reformate and distillate streams. Our approach involves refining multicomponent adsorption, mass transfer, and SMB process parameters based upon detailed experimental inputs, with progressive addition of components. We develop a robust model that quantitatively predicts the influence of key operating parameters such as stream flow rates, desorbent/feed ratio, and switch time on the separation results and concentration profiles. The model is validated as a function of feed complexity by SMB experiments and column concentration profile measurements in a 16‐column mini‐plant. Furthermore, conditions for clear separation of each mixture are developed. [ABSTRACT FROM AUTHOR]

• Separation technology with high selectivity for PGMs is necessary for increasingly complex and dilute recycling matrices. • PGM recycling is viable for many waste streams and solid phase recovery focuses on N-donor ligands and novel supports. • Selectivity and adsorption mechanisms differ but may be combined to improve capacity and selectivity. • Improvement of recycling and recovery processes from new waste streams will provide critical PGM for the green economy. • Opportunities include transitioning from model to real solutions and balancing selectivity with adsorption capacity. Platinum group metals (PGM) are a group of elements comprised of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), and rhodium (Rh) that are critical for use a wide variety of industries, and their demand will continue to increase with adoption of green energy technologies. This review will describe PGM found in ore and the use of PGM in catalysts, electronics, and fuel cells along with leaching solutions and conditions used for recovery of PGM from both primary and secondary sources. Adsorption has been identified as a promising technology for separating PGM from other base and noble metals from leaching solution due to the physical robustness, high selectivity, and easy tunability of adsorbents. Ligand families, solid supports, capacity, selectivity against base and noble metals, and mechanisms of adsorption found in current literature are described. [Display omitted] [ABSTRACT FROM AUTHOR]

The efficient separation of highly viscous crude oil/water mixtures caused by offshore crude oil exploitation, marine transportation, and oil recovery is still a big challenge. Adsorption and filtration techniques are considered as powerful and renewable approaches for oil/water separation because of their low cost and simple operation. However, conventional adsorption and filtration materials show poor separation performance due to the extremely high viscosity of crude oil. A variety of advanced adsorption and filtration materials have been developed very recently for the improvement of the crude oil/water separation performance, such as oil adsorption materials with in situ thermogenesis and filtration membranes with self‐cleaning property. In this review, the background of crude oil and crude oil/water mixtures are first described. Then, the fundamental wetting theories are also presented. Furthermore, the state‐of‐the‐art materials for viscous crude oil/water separation based on adsorption and filtration techniques are summarized respectively, including the separation mechanisms, strategies, fabrication methods, and separation performance. Finally, the conclusions and challenges for the viscous crude oil/water mixture separation are discussed. [ABSTRACT FROM AUTHOR]

We investigate hydrogen adsorption effects on stabilities and electronic properties of nitrogen defects in graphene using first-principles electronic-structure calculations within the density-functional theory. We find that the adsorption of hydrogen atoms on the pyridine-type nitrogen defects in graphene becomes energetically favorable, whereas in the case of the substitutional nitrogen defect the hydrogen adsorption becomes unfavorable. We also find that a transition from p-type to n-type doping properties occurs by hydrogen adsorption on the pyridine-type defects, suggesting that even the carrier type is controllable in nitrogen-doped graphene. [ABSTRACT FROM AUTHOR]

The authors have studied the influence of the adsorption and surface diffusion of one component of a binary gas mixture on pore walls on the effect of separation of the gas mixture during its flow through a nanosize porous membrane in a free molecular regime. A capillary porous-medium model obtained by the momentum-balance method was taken as a basis for analysis. Expressions have been determined for the separation factor and the concentration jump of the adsorbed component for an assigned pressure difference on the membrane, which make it possible to analyze the influence of the initial concentration of the adsorbable component and of the temperature on the separation effect. Calculations have been performed of the concentration jump for a number of commercial gas mixtures (CO2/H2, CO/H2, CH4/H2, and N2/He). It has been shown that taking account of surface diffusion may lead to appreciable variations (of several tens of percent) of the obtained values from Knudsen values of the effect in the absence of adsorption. [ABSTRACT FROM AUTHOR]

In this study, a facile way to prepare amphiphilic and asymmetric films with excellent mechanical properties for efficient and stable adsorption applications is reported. Non-solvent induced phase separation technology is developed to fabricate porous asymmetric poly(ether-blockamide) composite films. These films have a unique structure composed of a solid surface, a microporous surface, and hierarchical porous core, hence exhibiting prominent mechanical properties with an elongation at break up to 317% and mechanical resilience. Before and after 50-times cyclic stretching deformations, they still maintain intact porous structure, and their wetting angles of upper and lower surfaces to both water and cyclohexane are almost constant. Moreover, these films show excellent uptake for cyclohexane and water, and cyclic large deformations have little influence on the performance. It only takes 3 s to absorb 4 times of the weight of cyclohexane, while 1.8 times of water can be loaded within 134 s. [ABSTRACT FROM AUTHOR]

The activity in lattice-gas systems with geometric constraints is shown to be the ratio of the number of particles to the number of available sites. The key role of sites available for occupation is emphasized. Available sites may be different for different species and are not necessarily just unoccupied sites. Location-specific or non-local constraints are allowed. An analytical expression for the number of available sites is given for the hard-hexagon model. The utility of an expression for available sites is illustrated for the non-trivial case of a mixed Langmuir/hard-hexagon adsorption system, where the influence of the Langmuir adsorbates on the hard-hexagon phase transition is investigated. The dependence on available sites indicates how to extend these results to the kinetic regime and simulations of kinetic voltammograms for the hard-hexagon model are given as an example. [ABSTRACT FROM AUTHOR]

Pressure swing adsorption (PSA) is an important technology for mixture gas separation and purification. In this work, a dynamic model for a layered adsorption bed packed with activated carbon and zeolite 5A was developed and validated to study the PSA process. The model was validated by calculating breakthrough curves of a five-component gas mixture (H 2 /CH 4 /CO/N 2 /CO 2 = 56.4/26.6/8.4/5.5/3.1 mol%) and comparing the results with available experimental data. The purification performance of six-step layered bed PSA cycle was studied using the model. In order to optimize the cycle, the Box-Behnken design (BBD) method was used, as implemented in Design Expert™. The parametric study showed that, for adsorption step durations ranging from 160 to 200 s, as the adsorption time increased, the purity decreased, whereas the recovery and productivity increased. During the pressure equalization step, the purity increased as the pressure equalization time increased, but the recovery and productivity decreased for step durations ranging from 10 to 30 s. As the P/F ratio (hydrogen used in purge step to hydrogen fed in adsorption step) increased from 0.05 to 0.125, the purity increased, whereas the recovery and productivity decreased. The optimization of the layered bed PSA process by the BBD method was then performed. In addition to the adsorption time, the pressure equalization time and the P/F ratio were considered as independent optimization parameters. Quadratic regression equations were then obtained for three responses of the system, namely purity, recovery, and productivity. When purity is set as the main performance indicator, the following values were obtained for the optimization parameters: an adsorption time of 168 s, a pressure equalization time of 14 s, and a P/F ratio of 0.11. Under those conditions, the system achieved a purity of 99.99%, a recovery of 57.76%, and a productivity of 6.41 mol/(kg·h). • A layered bed pressure swing adsorption (PSA) model is developed and well validated. • Effects of adsorption time, pressure equalization time, P/F ratio are investigated. • Optimization based on Box-Behnken design (BBD) method for PSA cycle are studied. • Quadratic regression equations are obtained for purity, recovery, and productivity. • Optimal design parameters and performances are obtained under different strategies. [ABSTRACT FROM AUTHOR]

Isotopes of heavier gases including carbon (13C/14C), nitrogen (13N), and oxygen (18O) are highly important because they can be substituted for naturally occurring atoms without significantly perturbing the biochemical properties of the radiolabelled parent molecules. These labelled molecules are employed in clinical radiopharmaceuticals, in studies of brain disease and as imaging probes for advanced medical imaging techniques such as positronemission tomography (PET). Established distillation-based isotope gas separation methods have a separation factor (S) below 1.05 and incur very high operating costs due to high energy consumption and long processing times, highlighting the need for new separation technologies. Here, we show a rapid and highly selective adsorption-based separation of 18O2 from 16O2 with S above 60 using nanoporous adsorbents operating near the boiling point of methane (112 K), which is accessible through cryogenic liquefied-natural-gas technology. A collective-nuclear-quantum effect difference between the ordered 18O2 and 16O2 molecular assemblies confined in subnanometer pores can explain the observed equilibrium separation and is applicable to other isotopic gases. [ABSTRACT FROM AUTHOR]

The separation of C2H2 and CO2 is of industrial significance but is highly challenging due to their close similarities in physical–chemical properties. Metal–organic frameworks (MOFs) with tailored pore structures and tunable pore surfaces for the separation of C2H2/CO2 mixture are described in this perspective article. In terms of adsorption selectivity, MOF is classified into C2H2-selective MOF and CO2-selective MOF, which are discussed separately. Herein, we intend to present a short summary of the important advancements in C2H2/CO2 separation with MOFs. The relationship between the separation performance and structural features of MOFs, together with the separation mechanisms, has been discussed in detail. The challenges, research trends and opportunities in C2H2/CO2 separation with MOFs are highlighted. [ABSTRACT FROM AUTHOR]

Microporous metal organic framework NOTT‐210 was synthesized via solvothermal and dyes adsorption and separation properties were determined and discussed. NOTT‐210 with anion characteristic can selective adsorb low concentrations of cationic dyes from effluents at room temperature. And that NOTT‐210 can also separate the MB+ (methylene blue) and RB+ (rhodamine B) molecules because of size‐dependent effect and kinetics‐dependent effect. Hence, NOTT‐210 is among the very few porous MOFs which not only can adsorb low concentrations of MB+ and RB+ molecules but also has the ability to separate their mixture. [ABSTRACT FROM AUTHOR]

Grand-canonical Monte Carlo simulations were carried out to investigate the adsorption and separation of the binary mixture of CO2, SO2, and H2S in neutral and charged armchair single-walled carbon nanotubes (SWCNTs) at low pressures and 303 K. SWCNTs with diameter of 2.17, 2.71, and 3.26 nm and intertube distance of 1.0 nm were modeled. Fixed charges of −0.04 e to +0.04 e were placed on each nanotube carbon to investigate the effect of charge. It is found that the behaviors of CO2, SO2, and H2S as a component of the mixture in charged SWCNTs basically obey the same rules as they behave as pure gases. Due to the additional strong Coulomb force between the adsorbate and the charged SWCNTs, the adsorption quantity of the polar molecule (SO2 or H2S) are enhanced remarkably when mixed with CO2, while the adsorption of CO2 is usually suppressed as a result of adsorption competition in a limited space. As for the case of the mixture of SO2 or H2S, either of them can be enhanced or suppressed in the adsorption competition, depending on the sign of SWCNT charge. [ABSTRACT FROM AUTHOR]

Tartary buckwheat shell is an important by-product of Tartary buckwheat production. Previous studies shown that Tartary buckwheat shells are rich in flavonoids, which are responsible for their antioxidant properties. Due to lack of advanced separation technologies, the purification for Tartary buckwheat shell is still in the laboratory scale, and could not realize the industrialization production. According to the results of static adsorption experiment, AB-8 resin was selected for Tartary buckwheat shell flavonoids (TBSF) adsorption. The adsorption isotherm, resin adsorption thermodynamic and dynamic adsorption parameters were studied. And the adsorption of AB-8 resin for TBSF was determined as an endothermic process. Results of preparative chromatography experiment showed that TBSF could be efficiently purified by AB-8 resin. And the optimal parameters were: feed concentration 25 mg/mL, desorption flow rate 2.5 mL/min. Under these conditions, the TBSF were separated effectively. Results of liquid chromatography-mass spectrometer (LC-MS) indicated that there were seven kinds of flavonoids in Tartary buckwheat shell, which were mainly from the 40 and 60% of ethanol elution. Simulated moving bed (SMB) was applied for TBSF purification the first time in this study. The optimal conditions of SMB were as following: adsorption zone flow rate 7.0 mL/min, contaminant removal zone flow rate 17.9 mL/min, product elution zone flow rate 22.3 mL/min, regeneration zone flow rate 21.5 mL/min, water washing zone flow rate 27.5 mL/min, switching time 1260 S, and the purity and yield of TBSF was 90 ± 0.22% and 85 ± 0.28%, respectively. The IC50 values of α-glucosidase inhibition activities and DPPH scavenging activity of the purified TBSF were 57.09 ± 0.15 and 7.92 ± 0.23 μg/mL, respectively. The constituents of TBSF showed higher α-glucosidase inhibition activities and antioxidant than raw TBSF and rutin. The results suggest that SMB is a proper method for industrial production of TBSF, and SMB could be applied for other natural products purification. [ABSTRACT FROM AUTHOR]

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The adsorptions of Xe atoms on the Pd(111) and Cu(111) surfaces are investigated by first-principles calculations. The van der Waals interactions are considered in the optimization of the geometric structure. The equilibrium distance from the Xe atom to the topmost surface layer and the rumpling of the substrate are closer to the experimental data than by conventional calculations without including van der Waals interactions. The existence of the induced states, which are partially filled by electron back donation, is predicted by the calculated local density of states. The mechanism of the sublevel splitting of the 5p3/2 states is discussed. The differential electron densities are used to analyze the electron redistribution by the adsorption of Xe atoms. [ABSTRACT FROM AUTHOR]

Using aluminum oxide (Al2O3) films deposited by atomic layer deposition (ALD), the dominant passivation mechanisms at the c-Si/Al2O3 interface, as well as the chemical composition of the interface region, are investigated. The excellent surface passivation quality of thin Al2O3 films is predominantly assigned to a high negative fixed charge density of Qf = - (4 ± 1) × 1012 cm-2, which is located within 1nm of the Si/Al2O3 interface and is independent of the layer thickness. A deterioration of the passivation quality for ultrathin Al2O3 layers is explained by a strong increase in the interface state density, presumably due to an incomplete reaction of the trimethyl-aluminum (TMA) molecules during the first ALD cycles. A high oxygen-to-aluminum atomic ratio resulting from the incomplete adsorption of the TMA molecules is suggested as a possible source of the high negative charge density Qf at the Si/Al2O3 interface. [ABSTRACT FROM AUTHOR]

The electrical resistance of nanoporous gold prepared by dealloying is tuned by charging the surfaces of the porous structure in an electrolyte. Reversible variations in the resistance up to approximately 4% and 43% occur due to charging in the regimes of double layer charging and specific adsorption, respectively. Charging-induced variations in the electron density or of the volume cannot account for the resistance variation, indicating that this variation is primarily caused by charge-induced modifications of the charge carrier scattering at the solid-electrolyte interface. The relative resistance variation in nanoporous Au with surface charging is found to be much higher than reported for porous nanocrystalline Pt. This is due to the lesser resistance contribution from internal grain boundaries. The resistance variation in nanoporous Au is also higher than that found in thin films owing to the stronger surface scattering in the ligament structure compared to plan surfaces. We argue that the strong resistance variation in up to 43% in the regime of specific adsorption is due to the reversible formation of a chemisorbed surface layer acting as scattering centers for the charge carriers. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy (STM) topographical images and inelastic electron tunneling spectra (IETS) of a cis-2-butene molecule adsorbed on a Pd(110) surface have been simulated by first-principles calculations. Calculations have eliminated the ambiguity between the STM image and the adsorption orientation caused by the symmetry of the system and local chemical environment. A combination of STM images and IETS spectra has been shown to be particularly useful in determining the configuration of the molecule on the surface. [ABSTRACT FROM AUTHOR]

The interface between a fluid and a static wall is a useful model for a chemically heterogeneous solid-liquid interface. In this work, we outline the calculation of the wall-fluid interfacial free energy (γwf) for such systems using molecular simulation combined with adsorption equations based on Cahn’s extension of the surface thermodynamics of Gibbs. As an example, we integrate such an adsorption equation to obtain γwf as a function of pressure for a hard-sphere fluid at a hard wall. The results so obtained are shown to be in excellent agreement in both magnitude and precision with previous calculations of this quantity, but are obtained with significantly lower computational effort. [ABSTRACT FROM AUTHOR]

The Axilrod–Teller equation is incorporated into nonlocal density functional theory (NLDFT) to improve the description of low-temperature argon adsorption isotherm on graphitized carbon black. Using the NLDFT based on the Tarazona smoothed density approximation and the test-particle method, the pair and triplet distribution functions for liquid argon were analyzed. The latter allowed us to quantitatively account for the three-body Axilrod–Teller nonadditive term. An analogous scheme to that of Weeks, Chandler, and Andersen is proposed to incorporate the Axilrod–Teller equation into the NLDFT in the framework of mean field approximation. The three-body nonadditive term appeared to decrease the internal energy of liquid argon by about 5%, which is in agreement with molecular simulation results. The new approach has been applied to the vapor-liquid coexistence and to argon adsorption on graphitized carbon black at 87.3 K. The approach has been shown to fit the experimental adsorption isotherm within the relative error of about 4% as opposed to 37% in the case of the standard NLDFT. This is due to weakening of the intermolecular interaction potential by about 20% in the molecular layer nearest to the graphite surface resulted mainly from the positive Axilrod–Teller contribution of triplets comprising one carbon atom. [ABSTRACT FROM AUTHOR]

The method of dispersion correction as an add-on to standard Kohn–Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%–40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. [ABSTRACT FROM AUTHOR]

In nanochannel flows, the thermal resistance at the fluid-solid interface may depend on the flow scenario. In this work, we study the interfacial thermal resistance Rth in nanoscale force-driven flows at different temperatures and fluid-wall interactions. For Ar flows in Cu and Ag channels, the fluid-wall binding energy is strong and it is found that Rth assumes a maximum value as the external force is varied. The maximum value is caused by the fluid adsorption on the solid surfaces and the temperature increase in the fluid due to viscous frictions. However, when the fluid-wall interaction is weak, the maximum value is not observed and the interfacial thermal resistance decreases monotonously with increasing external force. With the presence of fluid adsorption, it is also found that the peak in Rth is more detectable at low temperature than high temperature. [ABSTRACT FROM AUTHOR]

We study the behavior of random AB-copolymer melts near a selective surface. We consider the case where the copolymers do not display phase segregation behavior in the bulk but the surface is strongly selective for the A-component and the probability of finding an A-monomer along the chain is p<1. Using self-consistent field theory and scaling arguments, we discuss some aspects of conformational rearrangements and composition selection in the surface layer. For strong selectivity we discuss the formation of a polydisperse brush on the surface. Next, we consider selection mechanisms of chains and sequences of A-species in the surface layer. We used the bond-fluctuation method to simulate copolymer melts at different values of the surface selectivity. Several aspects of the surface layer are analyzed, such as the composition profiles, chemical composition of chains on the surface, chain extension, and dynamics. We find evidence for conformational rearrangements in the surface layer according to the polydisperse brush model, as well as enrichment of A-monomers in the adosorbed chains, stretching of chains in the direction perpendicular to the surface, and selection of multiple A-sequences. Slight but systematic variation of the properties of surface layer at long simulation times indicates that selection processes require very long time scales as expected from theoretical arguments. [ABSTRACT FROM AUTHOR]

Theoretical investigations of the growth and growth rates of single-crystal nanowires (NWs) by vapor phase mechanisms have been carried out. Substrate-induced processes are assumed to dominate this growth. The modeling for growth takes adsorption, desorption, surface scattering, and diffusion into account. It takes into consideration also the retarding electric field arising from the scattering of the NW vapor species by both the substrate and the NW sidewalls. Growth characteristics under the influence of the retarding electric field have been studied. Competitive roles of adatom diffusivity and the electric field in the NW growth are elucidated. Influence of the growing NW length and the adatom impingement rate on the NW growth rate has been described. The effect of adatom collection area around each NW has been examined. The NW tapering and kinking have been explained. The fundamentals of the substrate induction and details of the growth parameters have been analyzed. The influence of foreign element catalytic agents in the vapor-liquid-solid mechanism has been presented. All these have led to the understanding and resolution of problems, controversies, and contradictions involving substrate-induced NW growths. [ABSTRACT FROM AUTHOR]

The adsorption of NO on Co(II)-exchanged chabazite (CHA), mordenite (MOR), and ferrierite (FER) has been investigated by periodic density functional theory calculations. The most stable configurations of Co(II) in α and β sites of the zeolites with two framework Al/Si substitutions at short distances and Al–(Si)n>1–Al ordering are used for calculating the adsorption energy of NO molecules on Co(II) cations and at Al framework sites. The less stable configurations of α-Co(II)-MOR/FER show larger adsorption energies for one and two NO molecules. The bonding of one, two (and three) NO molecules to α/β-Co(II) sites in CHA/MOR/FER induces a shortening of the N–O bond lengths because electron density is withdrawn from the antibonding orbital of the adsorbed NO molecule. The calculated ν(NO) stretching frequencies of mono- and dinitrosyl complexes at α/β-Co(II)-MOR/FER are in good agreement with the experimental data. NO molecules adsorbed on α-Co(II)-MOR and on α-Co(II)-FER show similar NO stretching frequencies as nitrosyl complexes in Co(II)-MOR/-FER/-ZSM-5. Mononitrosyl complexes of α/β-Co(II)-MOR/FER display ν(NO) frequencies blueshifted relative to the free NO, while in dinitrosyl complexes both the symmetric and asymmetric components are redshifted compared to the mononitrosyl frequency. The analysis of the vibrational spectra suggests that mononitrosyls are formed by adsorption at cation in both α and β sites in MOR, FER, and ZSM-5, while dinitrosyl complexes exist only at α-type Lewis sites. This is important for the understanding of the reduction mechanism of NO to N2. A larger adsorption capacity of α-Co(II)-FER compared to α-Co(II)-MOR is predicted. [ABSTRACT FROM AUTHOR]

In the present paper, the multicomponent adsorption of polyatomic species is described as a fractional statistics problem, based on Haldane’s statistics. Site exclusion is characterized by a “mutual exclusion matrix” g, which relates to the sizes of the different species and lattice geometry. The adsorption process has been monitored through total and partial isotherms, energy of adsorption and configurational entropy of the adsorbed phase. The thermodynamic functions calculated for a monomer-dimer mixture were applied to describe the adsorption of methane-ethane mixtures in zeolites. In the case of zero lateral interactions, the present approach was compared to the well-known ideal adsorbed solution theory. The results show that the treatment of this complex problem can be significantly simplified if looked up from the new theoretical perspective. [ABSTRACT FROM AUTHOR]

The NO chemisorption dynamics on ordered multilayer iron phthalocyanine (FePc) and quasiamorphous multilayer tetra-t-butyl FePc (ttbu-FePc) films on a Au(111) substrate was investigated using the King and Wells reflection technique. The NO zero coverage or initial sticking probabilities (S0) were measured as a function of sample temperature (Ts) and beam energy (Ei). The experimental results for both films show a monotonic decrease in S0 with increasing Ts and Ei consistent with NO adsorption occurring via a multiple pathway precursor-mediated mechanism in which the adsorbate initially physisorbs to the FePc organics, diffuses, and chemisorbs to the Fe metal center. The saturation coverage is 3% for the multilayer FePc surface and only 2% for the multilayer ttbu-FePc surface consistent with NO chemisorption occurring only on the Fe metal, where NO chemisorbs to 100% of the surface Fe metal centers. The reduced saturation coverage in the ttbu-FePc film is attributed to fewer Fe metal centers in the less dense ttbu-FePc films. A comparison of NO sticking on a multilayer FePc/Au(111) film with NO sticking on a monolayer FePc/Au(111) film shows that S0 is greater on the multilayer FePc film for all Ts and Ei, consistent with an increase in collision inelasticity for NO/multilayer FePc/Au(111). [ABSTRACT FROM AUTHOR]

We interpret the measured sensitivity difference of single walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) used as dielectric sensors of ammonia gas traces in terms of adsorption sites and effective coverages. The dielectric constant of a regular set of SWNTs deposited on a plane is compared to that of a single MWNT having the same size when the same pressure of ammonia molecules is applied on them. The corresponding resonance frequency shifts in the two sensors display an enhanced sensitivity of SWNT over the MWNT in excellent agreement with the experimental measurements. [ABSTRACT FROM AUTHOR]

Structural and electronic properties for oxygen-adsorbed graphene sheets have been explored using first-principles total-energy calculations within the local density functional theory. A finite energy gap emerges for the oxygen-adsorbed graphene and its value increases with the ratio of O/C, as manifested by experiments. Further, adsorption energy and migration barrier for oxygen atoms on the graphene sheet have been investigated. The results show that isolated oxygen atoms are highly mobile and incline to condense on the graphene sheet. [ABSTRACT FROM AUTHOR]

The signal enhancement of an easy to fabricate, nanoporous alumina assisted surface plasmon resonance (SPR) sensor is investigated. It is theoretically shown that the presence of a thin (under 200 nm) porous alumina layer on top of an aluminum film supporting the surface plasmons, may significantly increase (over one order of magnitude) the sensitivity of the SPR method in the case where the adsorption of relatively small molecules is probed. The comparative experimental investigation of self-assembled monolayer formation on planar metal films and porous alumina layers verifies the theoretical predictions. Based on these results, we discuss the extended applicability of this setup in biosensor and other related applications. [ABSTRACT FROM AUTHOR]

Platinum is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no platinum content is one of the grand challenges in fuel cell research. Here, we investigate electronic structures of Pt4 and Pt3Co clusters and report a comparative study of adsorption of H2, O2, and CO molecules on the two clusters using density functional theory. The adsorption studies show that H2 undergoes dissociative chemisorption on the tetrahedral clusters in head on and side on approaches at Pt centers. O2 dissociation occurs primarily in three and four center coordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O2 is found to be higher for the Co doped cluster. For CO, the Pt atop orientation is preferred for both Pt4 and Pt3Co tetrahedral clusters. Adsorption of CO molecule on tetrahedral Pt3Co in side on approach leads to isomerization to planar rhombus geometry. An analysis of Hirshfeld charge distribution shows that the clusters become more polarized after adsorption of the molecules. [ABSTRACT FROM AUTHOR]

We have studied the microscopic structure and the thermodynamic and electric properties of the restricted primitive model for electrolyte solutions in contact with a chemically modified uncharged and charged solid surface. The modification of the surface is performed by the tethering of chain particles via a specific single segment at the stage preceeding the adsorption of the restricted primitive model. Some fraction of segments belonging to a chain particle can be charged such that the system models adsorption on an electrode covered by an electrolyte brush. We apply the density functional method which combines previously developed approach for inhomogeneous chain fluids, and the weighted density mean spherical approximation energy route for the description of inhomogeneous ionic fluids. The theory is formulated in the semigrand canonical ensemble. Our principal findings are concerned with the density profiles of the species, the adsorption isotherms of ions in the presence of grafted chain particles, the charge density profile and the potential of zero charge (all as the functions of the grafted density), and other parameters related to the solid surface and its modification. [ABSTRACT FROM AUTHOR]

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidized Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO2 polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress, and interactions with single water molecules of a natively oxidized Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidized and amorphous silica surfaces of 97 and 90 mJ/m2, respectively, at a water adsorption coverage of approximately 1 ML. The difference arises from the stronger interaction of the natively oxidized surface with liquid water, resulting in a higher heat of immersion (203 vs 166 mJ/m2), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller densities with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account. [ABSTRACT FROM AUTHOR]

Using first-principles computations, we studied NH3 adsorption on a series of zigzag (n,0) single-walled BN nanotubes (BNNTs) and the effect of gas coverage. Tube diameter and NH3 coverage play important roles on the tube-NH3 interaction. Chemisorption of a single NH3 molecule on top of B site is energetically preferable for all the tubes studied, but the adsorption energy decreases sharply with increasing tube diameter, and then gradually approaches the value for NH3 physisorption on BN graphene layer. On the sidewall of (10,0) BNNT, NH3 molecules prefer to pair arrangement on top of B and N atoms opposite in the same hexagon. At low coverages, NH3 molecules are partly chemically bound to BNNTs. With the increase of NH3 coverage, hydrogen bonds form between the adsorbed NH3 molecules or between the NH3 molecules and N atoms in BNNTs. When the coverage reaches 25%, the chemisorption of NH3 transforms to physisorption completely. NH3 adsorption does not modify the overall band structures of BNNTs, irrespective of NH3 coverage, but the band gap is narrowed due to the NH3-tube coupling and tube deformation. [ABSTRACT FROM AUTHOR]

The adsorption and desorption kinetics of N2 on porous amorphous solid water (ASW) films were studied using molecular beam techniques, temperature programed desorption (TPD), and reflection-absorption infrared spectroscopy. The ASW films were grown on Pt(111) at 23 K by ballistic deposition from a collimated H2O beam at various incident angles to control the film porosity. The experimental results show that the N2 condensation coefficient is essentially unity until near saturation, independent of the ASW film thickness indicating that N2 transport within the porous films is rapid. The TPD results show that the desorption of a fixed dose of N2 shifts to higher temperature with ASW film thickness. Kinetic analysis of the TPD spectra shows that a film thickness rescaling of the coverage-dependent activation energy curve results in a single master curve. Simulation of the TPD spectra using this master curve results in a quantitative fit to the experiments over a wide range of ASW thicknesses (up to 1000 layers, ∼0.5 μm). The success of the rescaling model indicates that N2 transport within the porous film is rapid enough to maintain a uniform distribution throughout the film on a time scale faster than desorption. [ABSTRACT FROM AUTHOR]

The adsorption, desorption, and diffusion kinetics of N2 on thick (up to ∼9 μm) porous films of amorphous solid water (ASW) films were studied using molecular beam techniques and temperature programmed desorption. Porous ASW films were grown on Pt(111) at low temperature (<30 K) from a collimated H2O beam at glancing incident angles. In thin films (<1 μm), the desorption kinetics are well described by a model that assumes rapid and uniform N2 distribution throughout the film. In thicker films (>1 μm), N2 adsorption at 27 K results in a nonuniform distribution, where most of N2 is trapped in the outer region of the film. Redistribution of N2 can be induced by thermal annealing. The apparent activation energy for this process is ∼7 kJ/mol, which is approximately half of the desorption activation energy at the corresponding coverage. Preadsorption of Kr preferentially adsorbs onto the highest energy binding sites, thereby preventing N2 from trapping in the outer region of the film which facilitates N2 transport deeper into the porous film. Despite the onset of limited diffusion, the adsorption kinetics are efficient, precursor mediated, and independent of film thickness. An adsorption mechanism is proposed, in which a high-coverage N2 front propagates into a pore by the rapid transport of physisorbed second layer N2 species on top of the first surface bound layer. [ABSTRACT FROM AUTHOR]