The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Federico Romá - One of the best experts on this subject based on the ideXlab platform.
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A simple model for studying Multilayer Adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces.
The Journal of chemical physics, 2009Co-Authors: F.o. Sanchez-varretti, G.d. García, A. J. Ramirez-pastor, Federico RomáAbstract:In this work we study a simple model of Multilayer Adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces. A new approximate analytic isotherm is obtained and validated by comparing with Monte Carlo simulation in one- and two-dimensional lattices. Then, we use the well-known Brunauer-Emmet-Teller (BET) approach to analyze these isotherms and to estimate the monolayer volume, v(m). In this way, we confirm previous observations that the value of the v(m) obtained by the BET equation depends strongly on adsorbate size and surface heterogeneity. In all cases, we find that the use of the BET equation leads to an underestimate of the true monolayer capacity. Nevertheless, a compensation effect is found for the Adsorption on a patchwise bivariate surface, but this is not enough to eliminate the decrease of v(m) caused by the molecular size. In addition, we consider also the possibility to use the model to study the Adsorption on nanotube bundles.
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A simple statistical mechanical approach for studying Multilayer Adsorption of interacting rigid polyatomics
Surface Science, 2009Co-Authors: G.d. García, Federico Romá, F.o. Sanchez-varretti, A. J. Ramirez-pastorAbstract:Abstract A simple statistical mechanical approach for studying Multilayer Adsorption of interacting rigid molecular chains of length k (k-mers) has been presented. The new theoretical framework has been developed on a generalization in the spirit of the lattice-gas model and the classical Bragg–Williams (BWA) and quasi-chemical (QCA) approximations. The derivation of the equilibrium equations allows the extension of the well-known Brunauer–Emmet–Teller (BET) isotherm to more complex systems. The formalism reproduces the classical theory for monomers, leads to the exact statistical thermodynamics of interacting k-mers adsorbed in one dimension, and provides a close approximation for two-dimensional systems accounting multisite occupancy and lateral interactions in the first layer. Comparisons between analytical data and Monte Carlo simulations were performed in order to test the validity of the theoretical model. The study showed that: (i) the resulting thermodynamic description obtained from QCA is significantly better than that obtained from BWA and still mathematically handable; (ii) for non-interacting k-mers, the BET equation leads to an underestimate of the true monolayer volume; (iii) attractive lateral interactions compensate the effect of the multisite occupancy and the monolayer volume predicted by BET equation agrees very well with the corresponding true value; and (iv) repulsive couplings between the ad-molecules hamper the formation of the monolayer and the BET results are not good (even worse than those obtained in the non-interacting case).
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A new theoretical approach to Multilayer Adsorption of polyatomics
Surface Science, 2005Co-Authors: Federico Romá, A. J. Ramirez-pastor, J. L. RiccardoAbstract:Abstract The Multilayer Adsorption isotherms of linear particles ( k -mers) on homogeneous surfaces were developed on a generalization in the spirit of the well-known Brunauer–Emmet–Teller’s approach. The generalized equation is obtained through an analytical approach that provides the isotherm in the Multilayer regime from the isotherm in the monolayer regime. The formalism leads to exact results in one dimension and provides an analytical approximation to study Multilayer Adsorption on two-dimensional surfaces with different geometries (square, honeycomb and triangular). The entropic effects of the nonspherical character of the adparticles on the determination of the monolayer volume and Adsorption energy, are shown and discussed for type II and type III isotherms. Comparison with Monte Carlo simulations in the grand canonical ensemble and experimental Adsorption isotherms are used to test the accuracy and reliability of the model. Close agreement between simulated, theoretical and experimental results supports the applicability of the proposed model to describe Multilayer Adsorption in presence of multisite-occupancy.
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Multilayer Adsorption with multisite occupancy: An improved isotherm for surface characterization
Langmuir, 2002Co-Authors: J. L. Riccardo, A. J. Ramirez-pastor, Federico RomáAbstract:In this work, an improved solution for Multilayer Adsorption of linear species is presented. The particular case of Multilayer dimer Adsorption is dealt with in detail, and a new Adsorption isotherm is obtained for determination of surface area and Adsorption energy from experiments. From the comparison between the new isotherm and the standard Brunauer−Emmett−Teller (BET) formalism, it arises that the monolayer volume, vm (or the surface area, A), can be up to 1.5 times larger than the one from the BET model. The proposed model is simple and easy to apply in practice and leads to new values of surface area and Adsorption heat. Physically, these advantages are a consequence of properly considering the configurational entropy of the adsorbate.
M D Donohue - One of the best experts on this subject based on the ideXlab platform.
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theory of Multilayer Adsorption with correct critical behavior
Langmuir, 2003Co-Authors: G Aranovich L And, M D DonohueAbstract:It is shown that an expansion of the configurational energy in powers of density allows correcting the critical behavior of Ono−Kondo theory for Multilayer Adsorption. The proposed approach results in a new equation relating densities in each layer with density in the bulk. This equation predicts spinodals and binodals which are in excellent agreement with the exact phase diagram for a two-dimensional system and with the phase diagram known from Monte Carlo simulations for a three-dimensional system.
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Predictions of Multilayer Adsorption Using Lattice Theory
Journal of Colloid and Interface Science, 1997Co-Authors: Grigoriy L. Aranovich, M D DonohueAbstract:Abstract Multilayer Adsorption is calculated for a one-component vapor using ideas based on the Ono–Kondo lattice model. It is shown that this model predicts the common types of Adsorption behavior: the Henry, Langmuir, and Frumkin equations as particular cases; Multilayer isotherms including steps due to two-dimensional condensation; changes in the isotherm that occur when the temperature is varied from subcritical to supercritical conditions. In this paper, we investigate the Adsorption isotherm as the concentration approaches saturation conditions. The analysis shows that at conditions near saturation the Gibbs Adsorption has a weak divergence which can be described by either a logarithmic singularity or an exponential singularity with small exponent (less than 0.05).
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An equation of state for Multilayer Adsorption
Journal of Colloid and Interface Science, 1995Co-Authors: Grigoriy L. Aranovich, M D DonohueAbstract:An equation of state for Multilayer Adsorption is derived. This equation gives the correct thermodynamic behavior at small pressures and at the saturation vapor pressure. The equation of state is analyzed for weakly attractive and strongly attractive surfaces and results are compared with experimental data. In addition, a new relationship is obtained for the exponent d which describes the singularity in the Multilayer Adsorption isotherm. It is shown that d depends on temperature, saturation vapor pressure, Henry's coefficient, monolayer capacity, and surface tension.
A. J. Ramirez-pastor - One of the best experts on this subject based on the ideXlab platform.
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Modeling Multilayer Adsorption of interacting polyatomic species on heterogeneous surfaces
Physica A: Statistical Mechanics and its Applications, 2012Co-Authors: F.o. Sanchez-varretti, G.d. García, A. J. Ramirez-pastorAbstract:Abstract In the present work, a generalized lattice-gas model to study Multilayer Adsorption of interacting polyatomic species on heterogeneous surfaces is introduced. Using an approximation in the spirit of the well-known Brunauer–Emmet–Teller (BET) model, a new theoretical isotherm is obtained in one- and two-dimensional lattices and compared with Monte Carlo simulation. In addition, the BET approach is used to analyze these isotherms and to estimate the monolayer volume. In all cases, the application of the BET equation leads to an underestimate of the true monolayer capacity. However, significant compensation effects were observed for heterogeneous surfaces and attractive lateral interactions.
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A simple model for studying Multilayer Adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces.
The Journal of chemical physics, 2009Co-Authors: F.o. Sanchez-varretti, G.d. García, A. J. Ramirez-pastor, Federico RomáAbstract:In this work we study a simple model of Multilayer Adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces. A new approximate analytic isotherm is obtained and validated by comparing with Monte Carlo simulation in one- and two-dimensional lattices. Then, we use the well-known Brunauer-Emmet-Teller (BET) approach to analyze these isotherms and to estimate the monolayer volume, v(m). In this way, we confirm previous observations that the value of the v(m) obtained by the BET equation depends strongly on adsorbate size and surface heterogeneity. In all cases, we find that the use of the BET equation leads to an underestimate of the true monolayer capacity. Nevertheless, a compensation effect is found for the Adsorption on a patchwise bivariate surface, but this is not enough to eliminate the decrease of v(m) caused by the molecular size. In addition, we consider also the possibility to use the model to study the Adsorption on nanotube bundles.
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A simple statistical mechanical approach for studying Multilayer Adsorption of interacting rigid polyatomics
Surface Science, 2009Co-Authors: G.d. García, Federico Romá, F.o. Sanchez-varretti, A. J. Ramirez-pastorAbstract:Abstract A simple statistical mechanical approach for studying Multilayer Adsorption of interacting rigid molecular chains of length k (k-mers) has been presented. The new theoretical framework has been developed on a generalization in the spirit of the lattice-gas model and the classical Bragg–Williams (BWA) and quasi-chemical (QCA) approximations. The derivation of the equilibrium equations allows the extension of the well-known Brunauer–Emmet–Teller (BET) isotherm to more complex systems. The formalism reproduces the classical theory for monomers, leads to the exact statistical thermodynamics of interacting k-mers adsorbed in one dimension, and provides a close approximation for two-dimensional systems accounting multisite occupancy and lateral interactions in the first layer. Comparisons between analytical data and Monte Carlo simulations were performed in order to test the validity of the theoretical model. The study showed that: (i) the resulting thermodynamic description obtained from QCA is significantly better than that obtained from BWA and still mathematically handable; (ii) for non-interacting k-mers, the BET equation leads to an underestimate of the true monolayer volume; (iii) attractive lateral interactions compensate the effect of the multisite occupancy and the monolayer volume predicted by BET equation agrees very well with the corresponding true value; and (iv) repulsive couplings between the ad-molecules hamper the formation of the monolayer and the BET results are not good (even worse than those obtained in the non-interacting case).
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Multilayer Adsorption of Polyatomic Species on Homogeneous and Heterogeneous Surfaces
arXiv: Materials Science, 2008Co-Authors: F.o. Sanchez-varretti, G.d. García, A. J. Ramirez-pastor, F. RomaAbstract:In this work we study the Multilayer Adsorption of polyatomic species on homogeneous and heterogeneous bivariate surfaces. A new approximate analytic isotherm is obtained and validated by comparing with Monte Carlo simulation. Then, we use the well-known Brunauer-Emmet-Teller's (BET) approach to analyze these isotherms and to estimate the monolayer volume, $v_\mathrm{m}$. The results show that the value of the $v_\mathrm{m}$ obtained in this way depends strongly on adsorbate size and surface topography. In all cases, we find that the use of the BET equation leads to an underestimate of the true monolayer capacity.
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Multilayer Adsorption with multisite occupancy: An improved isotherm for surface characterization
Langmuir, 2002Co-Authors: J. L. Riccardo, A. J. Ramirez-pastor, Federico RomáAbstract:In this work, an improved solution for Multilayer Adsorption of linear species is presented. The particular case of Multilayer dimer Adsorption is dealt with in detail, and a new Adsorption isotherm is obtained for determination of surface area and Adsorption energy from experiments. From the comparison between the new isotherm and the standard Brunauer−Emmett−Teller (BET) formalism, it arises that the monolayer volume, vm (or the surface area, A), can be up to 1.5 times larger than the one from the BET model. The proposed model is simple and easy to apply in practice and leads to new values of surface area and Adsorption heat. Physically, these advantages are a consequence of properly considering the configurational entropy of the adsorbate.
A. J. Ramirez-pastor - One of the best experts on this subject based on the ideXlab platform.
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Irreversible Multilayer Adsorption of semirigid k-mers deposited on one-dimensional lattices.
Physical review. E, 2020Co-Authors: N De La Cruz Félix, A. J. Ramirez-pastor, P M Centres, E E Vogel, J F ValdésAbstract:Irreversible Multilayer Adsorption of semirigid k-mers on one-dimensional lattices of size L is studied by numerical simulations complemented by exhaustive enumeration of configurations for small lattices. The deposition process is modeled by using a random sequential Adsorption algorithm, generalized to the case of Multilayer Adsorption. The paper concentrates on measuring the jamming coverage for different values of k-mer size and number of layers n. The bilayer problem (n≤2) is exhaustively analyzed, and the resulting tendencies are validated by the exact enumeration techniques. Then, the study is extended to an increasing number of layers, which is one of the noteworthy parts of this work. The obtained results allow the following: (i) to characterize the structure of the adsorbed phase for the Multilayer problem. As n increases, the (1+1)-dimensional adsorbed phase tends to be a "partial wall" consisting of "towers" (or columns) of width k, separated by valleys of empty sites. The length of these valleys diminishes with increasing k; (ii) to establish that this is an in-registry Adsorption process, where each incoming k-mer is likely to be adsorbed exactly onto an already adsorbed one. With respect to percolation, our calculations show that the percolation probability vanishes as L increases, being zero in the limit L→∞. Finally, the value of the jamming critical exponent ν_{j} is reported here for Multilayer Adsorption: ν_{j} remains close to 2 regardless of the considered values of k and n. This finding is discussed in terms of the lattice dimensionality.
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Fractional statistical theory of finite Multilayer Adsorption
Applied Surface Science, 2016Co-Authors: Eduardo A. Takara, Evelina Quiroga, D. A. Matoz-fernandez, Nelio Ariel Ochoa, A. J. Ramirez-pastorAbstract:Abstract In the present paper, finite Multilayer Adsorption is described as a fractional statistics problem, based on Haldane's statistics. In this scheme, the Helmholtz free energy and its derivatives are written in terms of a parameter g, which relates to the configuration of the molecules in the adsorbed state. For values of g ranging between 0 and 1 the formalism is used to model experimental data of bovine serum albumin (BSA) adsorbed onto an ion exchange resin for different values of pH and temperature. Excellent agreement between theory and experiments was found.
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Multilayer Adsorption of Interacting Polyatomics on Heterogeneous Surfaces
arXiv: Statistical Mechanics, 2011Co-Authors: F.o. Sanchez-varretti, G.d. García, A. J. Ramirez-pastorAbstract:In the present work we introduce a generalized lattice-gas model to study the Multilayer Adsorption of interacting polyatomics on heterogeneous surfaces. Using an approximation in the spirit of the well-known Brunauer--Emmet--Teller (BET) model, a new theoretical isotherm is obtained in one- and two-dimensional lattices and compared with Monte Carlo simulation. In addition, we use the BET approach to analyze these isotherms and to estimate the monolayer volume. In all cases, we found that the use of the BET equation leads to an underestimate of the true monolayer capacity. However, significant compensation effects were observed for heterogeneous surfaces and attractive lateral interactions.
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A new theoretical approach to Multilayer Adsorption of polyatomics
Surface Science, 2005Co-Authors: Federico Romá, A. J. Ramirez-pastor, J. L. RiccardoAbstract:Abstract The Multilayer Adsorption isotherms of linear particles ( k -mers) on homogeneous surfaces were developed on a generalization in the spirit of the well-known Brunauer–Emmet–Teller’s approach. The generalized equation is obtained through an analytical approach that provides the isotherm in the Multilayer regime from the isotherm in the monolayer regime. The formalism leads to exact results in one dimension and provides an analytical approximation to study Multilayer Adsorption on two-dimensional surfaces with different geometries (square, honeycomb and triangular). The entropic effects of the nonspherical character of the adparticles on the determination of the monolayer volume and Adsorption energy, are shown and discussed for type II and type III isotherms. Comparison with Monte Carlo simulations in the grand canonical ensemble and experimental Adsorption isotherms are used to test the accuracy and reliability of the model. Close agreement between simulated, theoretical and experimental results supports the applicability of the proposed model to describe Multilayer Adsorption in presence of multisite-occupancy.
Nikom Klomkliang - One of the best experts on this subject based on the ideXlab platform.
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Multilayer Adsorption of benzene on graphitised thermal carbon black the importance of quadrupole and explicit hydrogen in the potential model
Chemical Engineering Science, 2012Co-Authors: Nikom Klomkliang, David Nicholson, Chaiyot Tangsathitkulchai, A. WongkoblapAbstract:Grand Canonical Monte Carlo (GCMC) simulation was used to study Multilayer Adsorption of benzene on graphitised thermal carbon black over a range of temperature between 273 K and 373 K. Three potential models for benzene were compared: TraPPE-UA-9, OPLS-AA and TraPPE-EH, in order to study their capability to correctly describe the Adsorption isotherms and isosteric heats. In the sub-monolayer region, there is no difference between the simulation results obtained with the three models, which all describe the experimental data well. However, in the Multilayer region only the TraPPE-EH model, that includes the quadrupole moment and explicit modelling of the hydrogen, is able to describe the experimental data accurately; the other two models significantly under-predict the data. The TraPPE-EH model was then used to investigate the microscopic behaviour of the adsorbed phase: the local density distribution and the orientation of various layers, particularly the change in orientation of benzene in the first layer with increase in loading from sub-monolayer to multi-layer. It was found that the orientation of benzene molecules in the first layer is affected by the presence of molecules in the higher layers, but that most benzene molecules remain in an orientation parallel to the surface, which is favoured by the interaction with the surface, while a smaller population takes 60° and verical orientations to the surface which maximises the entropy. The ratio of the number of molecules having parallel orientation to that having 60° and vertical orientations decreases in higher layers due to the weaker influence of the adsorbate–adsorbent interaction. Detailed study of the orientation shows that most slant and vertical molecules have two of their hydrogen atoms closer to the surface.
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Multilayer Adsorption of benzene on graphitised thermal carbon black—The importance of quadrupole and explicit hydrogen in the potential model
Chemical Engineering Science, 2012Co-Authors: Nikom Klomkliang, Duong D., David Nicholson, Chaiyot Tangsathitkulchai, A. WongkoblapAbstract:Grand Canonical Monte Carlo (GCMC) simulation was used to study Multilayer Adsorption of benzene on graphitised thermal carbon black over a range of temperature between 273 K and 373 K. Three potential models for benzene were compared: TraPPE-UA-9, OPLS-AA and TraPPE-EH, in order to study their capability to correctly describe the Adsorption isotherms and isosteric heats. In the sub-monolayer region, there is no difference between the simulation results obtained with the three models, which all describe the experimental data well. However, in the Multilayer region only the TraPPE-EH model, that includes the quadrupole moment and explicit modelling of the hydrogen, is able to describe the experimental data accurately; the other two models significantly under-predict the data. The TraPPE-EH model was then used to investigate the microscopic behaviour of the adsorbed phase: the local density distribution and the orientation of various layers, particularly the change in orientation of benzene in the first layer with increase in loading from sub-monolayer to multi-layer. It was found that the orientation of benzene molecules in the first layer is affected by the presence of molecules in the higher layers, but that most benzene molecules remain in an orientation parallel to the surface, which is favoured by the interaction with the surface, while a smaller population takes 60° and verical orientations to the surface which maximises the entropy. The ratio of the number of molecules having parallel orientation to that having 60° and vertical orientations decreases in higher layers due to the weaker influence of the adsorbate–adsorbent interaction. Detailed study of the orientation shows that most slant and vertical molecules have two of their hydrogen atoms closer to the surface.