A qualitative approach to adsorption mechanism identification on microporous carbonaceous surfaces

The paper presents results of research on identification of localized and other adsorption mechanisms, on geometrically heterogeneous graphite-like carbonaceous surfaces. It attempts to get an insight into properties of individual adsorptive molecule movement near attractive adsorption sites, arising from adsorbent surface geometrical heterogeneities. In particular, a shape and volume of space occupied by the continuously moving molecule mass center are investigated. To this aim, kinematic equilibrium of the particle moving near a hypothetical microporous carbonaceous adsorbent wall is considered, and then compared with thermodynamic equilibrium. The proposed approach enables to examine effects of certain surface geometry on the shape and volume of space occupied by adsorbed particles, and so to outline temperature conditions for the localized adsorption mechanism predomination. Thus, it provides a cognitive basis to answer the question, what particular mechanism (localized or other—e.g. mobile) should be assumed for a class of adsorption systems in order to select the most appropriate mathematical adsorption model. Hence, it makes it possible for more reliable examination of real porous structures, based on adsorption measurements.     

Adsorption properties and surface chemistry of MgO

The adsorption properties of MgO, which is used as a sorbent and catalyst support, were studied using gas chromatography. The test absorbents used were n-alkanes (which show only nonspecific dispersion interactions when physisorbed on any adsorbent) and adsorbates whose molecules are capable of specific interactions with the surface reactive sites of MgO. Adsorption isotherms were measured for CHCl₃, CH₃NO₂, CH₃CN, (CH₃)₂CO, CH₃COOC₂H₅, and (C₂H₅)₂O on MgO at 50–100°C. Differential molar enthalpy changes (?ΔH), equal to molar heats of adsorption, were determined. For polar adsorbates, contributions from dispersive and specific interactions into ?ΔH were determined. The electron-acceptor and electron-donor abilities of the MgO surface were estimated.     

Interactions between hydrogenated diamond surface and adsorbates with different concentration of NO2 molecules: A first‐principles study

To elucidate the effects of NO₂ and H₂O molecules on the surface conductivity of hydrogenated diamond film, models of various adsorbates containing different molecular ratio of NO₂ and H₂O on hydrogenated diamond (100) surfaces were constructed. The adsorption energies, equilibrium geometries of adsorbates, density of states, and atomic Mulliken populations were studied by using first‐principles method. The results showed that H₂O molecule in the adsorbate could weaken the interactions between the adsorbates and hydrogenated diamond surface significantly. Compared with H₂O molecule, NO₂ molecule relaxes more dramatically when adsorbed on hydrogenated diamond surface. In addition, density of states for C(100):H–2NO₂, C(100):H–NO₂, and C(100):H–NO₂ + H₂O systems are very similar to each other, which indicates an obvious peak at valence band maximum level for all the three samples. It can be attributed to mainly single occupied molecule orbital of NO₂ molecule and slightly C–H bond of C(100):H substrate. When the adsorbates contain one NO₂ and two H₂O molecules, the peak shifts slightly into valence band, but its intensity increases significantly. All the samples exhibit p‐type surface conductivity when adsorbed with pure NO₂ molecules, and the surface conductivity remains as H₂O molecules added into the NO₂ adsorbate layer. However, for oxygenated diamond surface, very week interactions generate between diamond surface and various adsorbates. All the oxygenated diamond (100) surfaces with various adsorbates containing different NO₂ and H₂O molecules on it exhibit an insulating property.     

Chromatographic Properties of HPLC Sorbents Modified with Zinc Octa-4,5-Carboxyphthalocyanate

The adsorption of the zinc octa-4,5-carboxyphthalocyanate modifier on known HPLC sorbents of different types (Silasorb-C₁₈, Diasorb-130-C₄, Diasorb-130-C₁₆, Spheron C 100 (LC), Spheron C 1000, and Hema S 1000 QL) was studied. The optimum conditions were determined for the modification of the sorbents in the static and dynamic modes. The mechanism of the retention of modifiers and adsorbates was considered, and the amount of the modifier on the surface of the adsorbents was calculated. The effect of the modifier on the retention of adsorbates was demonstrated. Mobile phases were selected for the selective and efficient separation of model mixtures of phenols.     

Adsorption of water isotopomers H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on hypercross-linked polystyrene MN-272

Adsorption of light and heavy water (H₂O and D₂O) on porous hypercross-linked polystyrene MN-272 was studied by gas chromatography. For the estimation of the properties of this polymer surface, n-alkanes (C6—C9), C_{6 6}, and polar compounds (CHCl₃, MeNO₂, MeCN, Me₂CO, EtCOOCH₃, Et₂O) were used as test adsorbates. The contributions of energies of dispersion and specific (donor-acceptor) intermolecular interactions to the total energy of adsorption were determined on the basis of experimental data on the retention of the sorbates. The electron-donor and electron-acceptor characteristics of the hypercross-linked polystyrene MN-272 surface were estimated. Hypercross-linked polystyrene MN-272 was found to be a weakly specific adsorbent with predomination of electron-donating properties. The adsorption isotherms of H₂O and D₂O were measured on this polymer at 50, 60, and 70 °C. The dependences of the isosteric heats of adsorption on the amount adsorbed were determined. The contribution of the energy of specific interactions to the total energy of adsorption for all polar adsorbates (except for acetone, light and heavy water) does not exceed 20%. Adsorption of H₂O on hypercross -linked polystyrene MN-272 is slightly weaker than that of D ₂O.     

A DFT study of H2O dissociation on metal‐precovered Fe (100) surface

The H₂O adsorption and dissociation on the Fe (100) surface with different precovered metals are studied by density functional theory. On both kinds of metal‐precovered surface, H₂O molecules prefer adsorb on hollow sites than bridge and top sites. The impurity energy difference is proportional to the adsorption energy, but the adsorbates are not sensitive to the adsorption orientation and height relative to the surface. The Hirshfeld charge analysis shows that water molecules act as an electron donor while the surface Fe atoms act as an electron acceptor. The rotation and dissociation of H₂O molecule occur on the Co‐ and Mn‐precovered surfaces. Some H₂O molecules are dissociated into OH and H groups. The energy barriers are about 0.5 to 1.0 eV, whose are consistence with the experimental data. H₂O molecules can be dissociated more easily at the top site on Co‐precovered surface 1 than that at bridge site on Mn‐precovered surface 2 because of the lower reaction barrier. The dispersion correction effects on the energies and adsorption configurations on Co‐precovered surface 1 were calculated by OBS + PW91. The dispersion contributions can improve a bit of the bond energy of adsorbates and weaken the hydrogen bond effect between adsorption molecules a little.     

Evaluation of defect induced surface heterogeneity in Metal-Organic Framework materials with alkali dopants employing adsorption isotherm modelling

In this article, an assessment of surface structural heterogeneity in porous metal organic framework (MOF) structure has been demonstrated by employing the methane and carbon-dioxide adsorption isotherms data. The virgin MIL-101-(Cr) MOF was synthesized by the hydrothermal method and defects were induced in the MOF structure by doping with various alkali (K, Na, Li) cations. The synthesized MOFs were characterized by XRD, SEM, EDX and BET measurement techniques. In order to understand the defect induced surface heterogeneity by alkali cation dopants, the surface energy distributions for CH₄ and CO₂ adsorptions on MOFs were measured by Dubinin – Astakhov model equation. The surface heterogeneity is mainly controlled by the limiting uptakes of adsorbates, the polarizability of adsorbates and the adsorbate-adsorbent interaction energy.     

The adsorption of H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on porous polystyrene adsorbents

The adsorption of H₂O and D₂O on porous polymers, Chromosorb-102 (styrene-divinylbenzene copolymer) and MN-200 (supercross-linked polystyrene), was studied by gas chromatography. Test adsorbates used to study the properties of the surface of these polymers were n-alkanes (C₆-C₉), C₆H₆, and the polar compounds CHCl₃, CH₃NO₂, CH₃CN, (CH₃)₂CO, C₂H₅COOCH₃, and (C₂H₅)₂O. The experimental data on the retention of the sorbates were used to determine the contributions of dispersion and specific intermolecular interactions to the total energy of adsorption for the systems studied. The electron donor K _D and electron acceptor K _A characteristics of the surfaces of Chromosorb-102 and MN-200 were determined. The K _D and K _A values obtained allow these polymers to be classified as weakly specific adsorbents with the predominance of electron acceptor properties. The adsorption isotherms of H₂O and D₂O were measured at 55, 67, and 80°C. The dependences of the isosteric heats of adsorption Q _st on adsorption values were determined. The conclusion was drawn that H₂O interacted with the surface of the polymers by the adsorption mechanism, whereas absorption likely made a noticeable contribution to the retention of D₂O.     

Correlation and Calculation of Multicomponent Adsorption Equilibria Data Using a Generalized Adsorption Isotherm

Enhanced by the need for reliable and accurate data of multicomponent gas adsorption equilibria on porous solids like activated carbons or zeolites, a new method to measure and correlate coadsorption equilibria has been developed. This method is a combination of gravimetric or volumetric measurements of the total load of pure or multicomponent adsorbates (Staudt, 1994; Gregg and Sing, 1982) and a correlation and calculation procedure using a new adsorption isotherm (AI) (Keller, 1990). This AI is thermodynamically consistent and describes adsorbates with fractal dimension for single- or multicomponent systems and load dependent adsorption energies. This method allows calculation of partial loads of multicomponent coadsorption equilibria from pure component data and the total loads of the mixture adsorption equilibria. This will be demonstrated for binary and ternary adsorption equilibria of CH₄, C₂H₄ and C₂H₆ on activated carbon (Reich et al., 1980).     

Reversible and irreversible adsorption of particles on homogeneous surfaces

The kinetics of localized reversible and irreversible adsorption of interacting particles on homogeneous surfaces was analysed. Asymptotic analytical equations were derived for the surface blocking parameter B(0), and for adsorption kinetics and adsorption isotherms in the limit of low and high surface concentrations. It was found that the geometrical blocking effect was much more pronounced than the Langmuir model predicts, especially for high surface concentrations and low ionic strengths of suspensions.The new adsorption isotherm formulated indicates that for a large adsorption constant, K_a, the equilibrium surface concentration becomes proportional to K^−1/3_a, whereas in the Langmuir model this quantity is approached as K⁻¹_a (for K_a ≫I). In the case of irreversible adsorption the theoretical predictions were experimentally tested by applying the direct microscope observation method. Monodisperse suspensions of negatively charged latex particles were used in these experiments with silanized mica sheets as the adsorbing surface. Our theoretical predictions were quantitatively confirmed, indicating that the Langmuir model is not appropriate for describing localized adsorption of particles on homogeneous surfaces.     

Activation and structural and adsorption features of activated carbons with highly developed micro-, meso- and macroporosity

Three sets of activated carbons (ACs) were prepared with the same precursor but activated differently (by CO₂ or water vapour) with various burn-off levels. The ACs demonstrate increased deviation of the pore shape from the slitshaped model with increasing burn-off and contributions of pores of different sizes depending on the activation type. Significant re-arrangement of adsorption complexes, especially of the Van der Waals type characteristic for nonpolar or weakly polar adsorbates (H₂, CH₄, CH₂Cl₂, CHCl₃), occurs in both micropores and mesopores of ACs with decreasing temperature. The behaviour of their mixtures with water and DMSO can strongly differ from that of individual adsorbates.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体. 作为可得的清洁能源,它的利用被认为是节能和经济的选择. 在本工作中,非金属原子X(X=H,O,N,S,P,Si,F,Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄,CO₂,H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中,H和Cl对CH₄的作用较大; N、O、F、Cl对CO₂的作用较强; N,Cl对H₂O的影响不容忽视. 总的来说,吸附能大小依次为：H₂O>CO₂>CH₄. 因此,在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附,进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体. 作为可得的清洁能源,它的利用被认为是节能和经济的选择. 在本工作中,非金属原子X(X=H,O,N,S,P,Si,F,Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄,CO₂,H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中,H和Cl对CH₄的作用较大; N、O、F、Cl对CO₂的作用较强; N,Cl对H₂O的影响不容忽视. 总的来说,吸附能大小依次为：H₂O>CO₂>CH₄. 因此,在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附,进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体. 作为可得的清洁能源,它的利用被认为是节能和经济的选择. 在本工作中,非金属原子X(X=H,O,N,S,P,Si,F,Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄,CO₂,H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中,H和Cl对CH₄的作用较大; N、O、F、Cl对CO₂的作用较强; N,Cl对H₂O的影响不容忽视. 总的来说,吸附能大小依次为：H₂O>CO₂>CH₄. 因此,在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附,进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体. 作为可得的清洁能源,它的利用被认为是节能和经济的选择. 在本工作中,非金属原子X(X=H,O,N,S,P,Si,F,Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄,CO₂,H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中,H和Cl对CH₄的作用较大; N、O、F、Cl对CO₂的作用较强; N,Cl对H₂O的影响不容忽视. 总的来说,吸附能大小依次为：H₂O>CO₂>CH₄. 因此,在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附,进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.