Adsorption Energy Distribution Function Research Articles

Surface properties of clinker phases and clay minerals characterized by inverse gas chromatography (IGC) and their link to reactivity

This paper presents a preliminary study of the characterization of the surface energy properties of clinker phases (C3S and C3A), kaolin and metakaolin by Inverse Gas Chromatography (IGC). For this, a reliable measurement methodology was developed. By looking at changes in the whole series of results (dispersive surface energy, specific polar interaction parameter, acid and base constants, morphology index, nanoroughness and adsorption energy distribution function), it is possible to discern changes between the same powders with different surface treatments. A promising correlation between surface properties and the reactivity of studied materials have been found. However, based on the IGC characterization, the increased reactivity of metakaolin compared to the raw kaolinite seems to be strongly linked to the change in local order rather than significant changes in the surface energetics, although a change in the acid/base nature of the surface has been observed.

Effects of sodium chloride on mechanical properties in amorphous polymers of waterlogged archaeological wood: Insights from molecular dynamics simulations

Sodium chloride (NaCl) is the main soluble salt component of marine waterlogged archaeological wood, and it causes deterioration of wood fibres. In this study, a molecular dynamics simulation of three types of archaeological wood from the Quanzhou Song Shipwreck was employed to investigate the impact of NaCl on the mechanical properties of amorphous components consisting of amorphous cellulose, hemicellulose, and lignin. The findings revealed that water molecules bound to the fibres enhanced the mechanical performance of the woody fibres. However, NaCl affected the stability and mechanical properties of the amorphous components. By using molecular dynamics simulations, 24 sets of amorphous fibre models, consisting of fir, pine, and camphorwood with salt concentrations ranging from 0 % to 7 %, were constructed to further analyse the influence of salt content on the mechanical properties of the amorphous components. The results showed that all three species of archaeological wood exhibited similar trends, with the adsorption energy and radial distribution function between wood fibres and water molecules decreasing with increasing NaCl concentration, leading to the gradual rupture of hydrogen bonds in water molecules. Consequently, more water molecules engage in ion hydration, resulting in an increase in the amount of free water within the amorphous regions. This, in turn, degrades the mechanical properties of the amorphous components. This study contributes significantly to a comprehensive understanding of the mechanical properties of marine archaeological wood and is important for decision-making in studies related to the preservation and evaluation of marine waterlogged wooden artefacts.

폐 PET 기반 활성탄의 CO2 및 N2 흡착특성

In this study, waste polyethylene terephthalate (PET) based activated carbon (AC) with different textural properties were prepared by adjusting the KOH mixing ratio. The prepared ACs were characterized by SEM, TEM, XRD, XPS and nitrogen adsorption analysis. From the characterization results, ACs showed a good correlation between the KOH mixing ratio and the surface area, pore volume and pore size, but there was no correlation with the surface chemical composition. In addition, the adsorption equilibrium amount of CO₂ and N₂ was measured under different temperature and pressure conditions using a volumetric adsorption apparatus. The adsorption amount of the target gas showed a good correlation with the ultramicropore volume (V_{<0.9 nm}) rather than the surface area and total pore volume of ACs. The gas adsorption behaviors according to the pore structure were compared and analyzed by adsorption isotherm models, isosteric heat of adsorption, and adsorption energy distribution function (AED). The selectivity for CO₂ calculated using the ideal solution theory (IAST) under flue gas (CO₂ : N₂ = 15 : 85) conditions suggests that the waste PET-based AC can be sufficiently used for the related CO2 adsorptive separation process.

Molecular dynamics study of three amino acids as corrosion inhibitor for copper in hydrochloric acid solution.

Molecular dynamics (MD) simulation is used to study the corrosion inhibition mechanism of cysteine (Cys), glutamic (Glu) and glycine (Gly) for copper in hydrochloric acid solution. The adsorption energy and radial distribution function results show that all three amino acids can spontaneously adsorb on Cu (111) surface by chemical adsorption. The absolute value of adsorption energy and intensity is Cys > Glu > Gly. The diffusion coefficient and relative concentration curve show that all the three amino acids can inhibit the diffusion and aggregation ability of corrosion particles, so the three amino acids not only can slow down the aggregation of corrosive particles, but also effectively repel corrosive particles to protect the substrate. The inhibition ability obtained by the MD simulation shows the trend of Cys > Glu > Gly, which is consistent with the experimental results. The inhibition efficiency is determined by both the adsorption strength on the substrate surface and inhibition ability for the diffusion and aggregation ability of corrosion particles.

Adsorption characteristics of light gases on basalt rock-based zeolite 4A

The adsorption characteristics of light gases on basalt rock-based zeolite 4A (BR zeolite-4A) were systematically investigated to evaluate its potential application as an alternative adsorbent for adsorption-based separation processes. We used alkali fusion and hydrothermal procedure to prepare the nanostructured adsorbent, BR zeolite-4A, which was characterized with field emission scanning electron microscopy, X-ray diffraction, and carbon dioxide adsorption apparatus. The single component adsorption equilibrium for CO2, CH4, N2 and H2 on the BR zeolite-4A was volumetrically determined using a nanoPOROSITY adsorption analyzer at the temperature range from (288.15 to 308.15) K and pressure range from (0.1 to 110) kPa. The experimental results indicate that BR zeolite-4A showed higher adsorption capacities for CO2 compared to other light gases, indicating the suitable porous material for selective separation by adsorption. Three different isotherm equations, Langmuir, Toth, and Sips, were used to correlate the adsorption isotherm data and the most reasonable results obtained from the Sips model irrespective of the adsorption isotherm types. Isosteric heat of adsorption and adsorption energy distribution function values were calculated and used to further examine the surface energetic heterogeneity of BR zeolite-4A. The pure component adsorption isotherm results were also used to predict the adsorption selectivity for CO2/N2, CO2/CH4, CO2/H2, and CH4/H2 binary mixtures (50:50) at different pressure ranges using ideal adsorbed solution theory.

Solving the adsorption integral equation with Langmuir-kernel and the influence of temperature on the stability of the solution

Adsorption energy distribution functions can be calculated from measured adsorption isotherms by solving the adsorption integral equation. In this context, it is common practice to use general regularization methods, which are independent of the kernel of the adsorption integral equation, but do not permit error estimation. In order to overcome this disadvantage, we present in this paper a solution theory which is tailor-made for the Langmuir kernel of the adsorption integral equation. The presented theory by means of differentiation and Fourier series is the basis for a regularization method with explicit terms for error amplification. By means of simple and complicated adsorption energy distribution functions we show for ideal gas adsorption isotherms without measurement error that reliable distribution functions can be obtained from the isotherms. Furthermore we show how the stability of the solution depends on temperature.

Heterogeneity of multiwalled carbon nanotubes based on adsorption of simple aromatic compounds from aqueous solutions

The surface heterogeneity of multiwalled carbon nanotubes (MWCNTs) is studied on the basis of adsorption isotherms from dilute aqueous phenol and dopamine solutions at various pH values. The generalized Langmuir–Freundlich isotherm equation was applied to investigate the cooperative effect of the surface heterogeneity and the lateral interactions between the adsorbates. The theoretical isosteric heats of adsorption were obtained assuming that the heat of adsorption profile reveals both the energetic heterogeneity of the adsorption system and the strength of the interactions between the neighboring molecules. The adsorption energy distribution functions were calculated by using algorithm based on a regularization method. The great advantage of this method is that the regularization makes no assumption about the shape of the obtained energy distribution functions. Analysis of the isosteric heats of adsorption for MWCNTs showed that the influence of the surface heterogeneity is much stronger than the role of the lateral interactions. The most typical adsorption heat is 20–22 kJ/mol for both phenol and dopamine. After purification of nanotubes, heat value for phenol dropped to 16–17 kJ/mol. The range of the energy distribution is only slightly influenced by the surface chemistry of the nanotubes in the aqueous conditions.

Energetic investigation of the adsorption process of CH4, C2H6 and N2 on activated carbon: Numerical and statistical physics treatment

The adsorption energy distribution (AED) function of a commercial activated carbon (BDH-activated carbon) was investigated. For this purpose, the integral equation is derived by using a purely analytical statistical physics treatment. The description of the heterogeneity of the adsorbent is significantly clarified by defining the parameter N′m(E). This parameter represents the energetic density of the spatial density of the effectively occupied sites. To solve the integral equation, a numerical method was used based on an adequate algorithm. The Langmuir model was adopted as a local adsorption isotherm. This model is developed by using the grand canonical ensemble, which allows defining the physico-chemical parameters involved in the adsorption process. The AED function is estimated by a normal Gaussian function. This method is applied to the adsorption isotherms of nitrogen, methane and ethane at different temperatures. The development of the AED using a statistical physics treatment provides an explanation of the gas molecules behaviour during the adsorption process and gives new physical interpretations at microscopic levels.

Thermogravimetry Q-TG studies of surface properties of lunar nanoparticles

Using special thermogravimetry Q-TG method, physicochemical properties of lunar sample surfaces were investigated. The numerical and analytical procedures for the evaluation of energetic heterogeneous properties on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The calculations of the adsorption capacity and energy distribution functions of liquids on lunar surfaces on the basis of the thermogravimetry data are presented.

Adsorption and Thermo Desorption Characteristics of Hydrocarbons on Single Walled Carbon Nanotubes

We investigated the heterogeneous adsorption and thermal desorption behaviors of acetone, n-hexane and trichloroethylene (TCE) on single walled carbon nanotubes (SWCNTs). Adsorption isotherms for selected molecules on SWCNTs were measured using a quartz spring balance at temperatures ranging from 303.15 to 323.15 K. Thermal gravimetric desorption experiments were also conducted at different heating rates (2-10 K/min) to obtain information about the interaction strength of hydrocarbons with SWCNTs surfaces. The adsorption isotherm data were analyzed successfully with the temperature dependent Toth equation. To obtain the adsorption and desorption energy distribution functions (AED/DED) for hydrocarbons and nitrogen, the integral equation with Fowler-Guggenheim isotherm (for AED) and first order desorption rate equation (for DED) were solved using the generalized nonlinear regularization method. It was found that Henry's constants, the isosteric heats of adsorption, and the pattern of energy distribution function were highly dependent on the polarizability.

Heterogeneous adsorption and catalytic oxidation of benzene, toluene and xylene over spent and chemically regenerated platinum catalyst supported on activated carbon

The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H 2SO 4) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption–desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H 2SO 4 aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H 2SO 4 treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H 2SO 4 treated Pt/AC catalyst follows the sequence of benzene > toluene > o-xylene. The adsorption equilibrium isotherms of BTX on the H 2SO 4 treated Pt/AC were measured at different temperatures ranging from 120 to 180 °C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H 2SO 4 treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H 2SO 4 treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions.

Relation between adsorption and catalysis in the case of NiO and Co 3O 4

Reversed flow-inverse gas chromatography is a quick, precise and effective methodology to characterize physicochemical properties of adsorbents. This is extended to the experimental measurement of the adsorption energy distribution function as well as of the differential energy of adsorption due to lateral interactions of molecules adsorbed on two catalysts, namely Co 3O 4 and NiO. Thus, the nature and the strength of the adsorbate–adsorbent and adsorbate–adsorbate interactions are extracted in order to give detailed answers to the questions: (a) where are the molecules on the heterogeneous surface and (b) which is the nature of the surface chemical bonds? Thus, adsorption of 1-butene was found to take place immediately and irreversibly. It holds a deep relation between adsorption and catalysis of 1-butene over these catalysts. As a consequence, the adsorption of 1-butene in the presence of hydrogen leads to isobutane and/or n-butane, depending on the temperature. It can be seen from the adsorption/desorption kinetic constants that the adsorption of 1-butene on Co 3O 4 is one order higher than over NiO. This fact in connection with the bigger activation energy and the lower kinetic coefficients concerning hydrogenation reaction over NiO shows that Co 3O 4 is a better catalyst for this kind of catalysis.

Comparison of the adsorption mechanisms of pyridine in hydrophilic interaction chromatography and in reversed-phase aqueous liquid chromatography

The adsorption isotherms of pyridine were measured by frontal analysis (FA) on a column packed with shell particles of neat porous silica (Halo), using water–acetonitrile mixtures as the mobile phase at 295 K. The isotherm data were measured for pyridine concentrations covering a dynamic range of four millions. The degree of heterogeneity of the surface was characterized by the adsorption energy distribution (AED) function calculated from the raw adsorption data, using the expectation-maximization (EM) procedure. The results showed that two different retention mechanisms dominate in Per aqueous liquid chromatography (PALC) at low acetonitrile concentrations and in hydrophilic interaction chromatography (HILIC) at high acetonitrile concentrations. In the PALC mode, the adsorption mechanism of pyridine on the silica surface is controlled by hydrophobic interactions that take place on very few and ultra-active adsorption sites, which might be pores on the irregular and rugose surface of the porous silica particles. The surface is seriously heterogeneous, with up to five distinct adsorption sites and five different energy peaks on the AED of the packing material. In contrast, in the HILIC mode, the adsorption behavior is quasi-homogeneous and pyridine retention is governed by its adsorption onto free silanol groups. For intermediate mobile phase compositions, the siloxane and the silanol groups are both significantly saturated with acetonitrile and water, respectively, causing a minimum of the retention factor of pyridine on the Halo column.

Effect of grooves on adsorption of RGD tripeptide onto rutile TiO2 (110) surface

Molecular dynamics (MD) simulations have been performed to investigate the adsorption mechanism of Arg-Gly-Asp (RGD) tripeptide onto perfect and grooved rutile TiO(2) (110) surfaces, respectively. The simulation results suggest that RGD tripeptide can strongly adsorb onto TiO(2) surface through specified Ti coordination sites. Analysis of adsorption energy, mean-squared displacements and radial distribution functions indicates that the adsorption of RGD onto grooved surface is more stable and rapid than that onto the perfect surface, with the adsorption energy around -331.59 kcal/mol. And among the chosen groove surfaces, adsorption energies, adsorption speeds and adsorption depths of RGD onto the surfaces increase evidently with the extension of groove dimensions. For both perfect and grooved surfaces, once bonded to the surfaces by interactions of carboxyl groups or carbonyl groups with nearby surface Ti atoms, RGD tripeptides show a reasonable propensity to remain there and undergo relatively limited hinge-bending motions.

Application of the Statistical Rate Theory of interfacial transport to investigate the kinetics of mixed-gas adsorption onto the energetically homogeneous and strongly heterogeneous surfaces

Kinetics of mixed-gas adsorption by using the Statistical Rate Theory is studied. Applying the adsorption lattice model two cases are investigated: when adsorption occurs like on the homogeneous surface and when energetic heterogeneity of adsorption system can be described by the rectangular adsorption energy distribution function. The model of calculations offers possibility of theoretical prediction of the rate of adsorption/desorption of mixture components by using the single-gas equilibrium and kinetic data. Possible changes of adsorbate concentration near the adsorbing surface are also taken into account. The obtained theoretical expressions were verified using real adsorption systems.

The Study of Adsorption of Iodine on Carbon Black by Inverse Liquid Chromatography

Abstract The study of iodine adsorption on carbon black samples was made using inverse liquid chromatographic frontal analysis (ILC). Unlike HPLC supports, the efficiency of the chromatographic column filled with a carbon black designed for rubber applications is low. Then the front boundaries of a non-adsorbed molecule, like heavy water (D2O) or acetone, was taken as reference for the calculation of the desorption isotherms. The monolayer capacity of adsorption, Langmuir's and Henry's constants were determined from the desorption isotherms. It was observed that 40% of the surface of the studied carbon black corresponds to a phenomenon of irreversible adsorption of the probe, and that the ILC also highlighted the heterogeneity of the studied carbon black. The adsorption energy distribution functions of iodine obtained by this method are similar to those which were already determined by IGC-FC with the heptane -like probe. The differences in behaviors between two families of carbon black could be attributed to the surface roughness.

Validation of Simple Equations Describing the Adsorption of Binary Gas Mixtures onto Surfaces with an Asymmetric Distribution of Adsorption Energy

The Monte Carlo simulation method was used to test the accuracy of approximate equations derived for binary gas adsorption onto a heterogeneous surface characterized by a Dubinin-Astakhov adsorption energy distribution (AED) function. In particular, the Condensation Approximation (CA) was applied to obtain simple equations for the partial adsorption isotherms and phase diagrams in the system for which a separate AED was assumed for each component of the mixture. A few cases involving different relationships between the AEDs associated with the adsorbing components were discussed. Additionally, the results of the proposed theory were compared with exact numerical solutions obtained using the Integral Equation method. From both simulations and numerical calculations, it follows that, in general, the CA is not appropriate for the prediction of binary adsorption equilibria when the individual AEDs are of an entirely different shape. On the other hand, when the AEDs were microscopically correlated, i.e. when the adsorption energy of one component on every site was shifted by a constant value compared to that of the other, the phase diagrams obtained were found to be in a very good agreement with their simulated counterparts.

Energetic surface heterogeneity of nanocrystalline TiO2 films for dye-sensitized solar cells

Dye sensitized solar cells (DSSCs) have been receiving significant attention because they have many advantages compared to conventional organic solar cells. It has been known that the photovoltaic characteristics of DSSC are highly dependent on the adsorption properties of dyes on TiO2 films. To analyze the surface heterogeneity of TiO2 surfaces, single-phase anatase nanocrystallite titanium films were prepared by sol-gel method using the hydrolysis reaction of titanium tetraisopropoxide under acidic condition and characterized by XRD, FE-SEM and BET analysis. The adsorption energy distribution functions were calculated by the generalized nonlinear regularization method. It was found that the shape and the intensity of the adsorption energy distribution curve determined were highly related with the physical properties (i.e., geometrical heterogeneity) and chemical characteristics (i.e., energetic heterogeneity) of nanocrystalline TiO2 for DSSC.

Chiral separation on a model adsorbent with periodic surface heterogeneity

Optimization of enantioselectivity in heterogeneous catalysis and chiral chromatography is a challenging task for the production of enantiopure chemicals. Enantioselective adsorbents usually consist of a surface with chiral receptors being either chiral molecules linked to the surface or chiral pockets formed by molecular templating of the surface. In both cases, the enantioselectivity is controlled mainly by the strength of the receptor-enantiomer interaction, such that one-to-one correspondence is usually preserved. The authors use Monte Carlo calculations to show that this steric requirement is not a necessary condition for the effective separation of chiral molecules. In particular, they propose a way in which a chiral surface can be constructed by a suitable spatial distribution of active sites for which the classical concept of a chiral receptor is no longer useful. Their calculations indicate that the effectiveness of the separation is affected mainly by the difference in shape of the adsorption energy distribution functions corresponding to the enantiomers.

Adsorption of Hydrogen and Methane Mixtures on Carbon Cylindrical Cavities

The purpose of this work is to provide some insights into the adsorption of hydrogen and methane mixtures on carbon cavities with cylindrical geometry. Hydrogen and methane mixture adsorption has been simulated in pore sizes ranging from micropores to mesopores at room temperature. The grand canonical Monte Carlo method provided the amount adsorbed as a function of pressure and bulk composition. In addition, the microscopic characteristics of the adsorbed phase have been accomplished by calculating density profiles and adsorption energy distribution functions. The results show that the first methane and hydrogen adsorbed layers are co-incident, and there is a second hydrogen layer that is not present in the pure compound adsorption. In addition, the adsorption energy stages for hydrogen in the mixture are more favorable than those for pure hydrogen, revealing that the presence of methane molecules favors energetic hydrogen stabilization (for micropores, hydrogen adsorption energy changes are observed from 6.3 to 75%, depending on the operational conditions). These results can shed light on the knowledge of the underlying adsorption behavior of these mixtures, which are of interest in hydrogen storage and purification by adsorption, and therefore of potential applications in hydrogen technology (clean hydrogen production, fuel cells, etc.).