Adsorption computer simulation

Reddy G, Yethiraj A (2010) Solvent effects in polyelectrolyte adsorption computer simulation with explicit and implicit solvent. J Chem Phys 132 074903. doi 10.1063/1.3319782... 

Because of the lack of a general theory of adsorption, computer simulations have greatly contributed to the understanding of adsorption on heterogeneous solids. Monte Carlo simulations have already shown their abihty to perform with the success in this area of research. In general, computer simulations are ideally suited to answer fundamental questions firom a theoretical perspective. Based on a microscopic model of the system, computer simulations... 

A. de Keizer, T. Michalski, G. H. Findenegg. Fluids in pores experimental and computer simulation studies of multilayer adsorption, pore condensation and critical point shifts. Pure Appl Chem (55 1495-1502, 1991. 

D. Nicholson, N. D. Parsonage. Computer Simulation and the Statistical Thermodynamics of Adsorption. New York Academic Press, 1983. 

Computer Simulations and Theory of Adsorption on Energetically and Geometrically Heterogeneous Surfaces... 

Both extreme models of surface heterogeneity presented above can be readily used in computer simulation studies. Application of the patch wise model is amazingly simple, if one recalls that adsorption on each patch occurs independently of adsorption on any other patch and that boundary effects are neglected in this model. For simplicity let us assume here the so-called two-dimensional model of adsorption, which is based on the assumption that the adsorbed layer forms an individual thermodynamic phase, being in thermal equilibrium with the bulk uniform gas. In such a case, adsorption on a uniform surface (a single patch) can be represented as... 

FIG. 2 Distribution of the adsorption energy (a) and of the adsorbate-adsorbate interaction energy (b) for the adsorbed Ar atoms obtained from computer simulations at r = 90 K. (Reprinted with permission from Langmuir 5 148-154, August 1992. 1992, American Chemical Society.)... 

At this point we should also recall another application of the already mentioned Bernal model of amorphous surface. Namely, Cascarini de Torre and Bottani [106] have used it to generate a mesoporous amorphous carbonaceous surface, with the help of computer simulation and for further application to the computer simulation study of adsorption. They have added a new component to the usual Bernal model by introducing the possibility of the deletion of atoms, or rather groups of atoms, from the surface according to some rules. Depending on the particular choice of those rules, surfaces of different porosity and structure can be obtained. In particular, they have shown examples of mono- as well as pohdispersed porous surfaces... 

Another special case of weak heterogeneity is found in the systems with stepped surfaces [97,142-145], shown schematically in Fig. 3. Assuming that each terrace has the lattice structure of the exposed crystal plane, the potential field experienced by the adsorbate atom changes periodically across the terrace but exhibits nonuniformities close to the terrace edges [146,147]. Thus, we have here another example of geometrically induced energetical heterogeneity. Adsorption on stepped surfaces has been studied experimentally [95,97,148] as well as with the help of both Monte Carlo [92-94,98,99,149-152] and molecular dynamics [153,154] computer simulation methods. 

D. Nicholson, N. G. Parsonage. Computer Simulations and Statistical Mechanics of Adsorption. London Academic Press, 1982. 

In Sec. 3 our presentation is focused on the most important results obtained by different authors in the framework of the rephca Ornstein-Zernike (ROZ) integral equations and by simulations of simple fluids in microporous matrices. For illustrative purposes, we discuss some original results obtained recently in our laboratory. Those allow us to show the application of the ROZ equations to the structure and thermodynamics of fluids adsorbed in disordered porous media. In particular, we present a solution of the ROZ equations for a hard sphere mixture that is highly asymmetric by size, adsorbed in a matrix of hard spheres. This example is relevant in describing the structure of colloidal dispersions in a disordered microporous medium. On the other hand, we present some of the results for the adsorption of a hard sphere fluid in a disordered medium of spherical permeable membranes. The theory developed for the description of this model agrees well with computer simulation data. Finally, in this section we demonstrate the applications of the ROZ theory and present simulation data for adsorption of a hard sphere fluid in a matrix of short chain molecules. This example serves to show the relevance of the theory of Wertheim to chemical association for a set of problems focused on adsorption of fluids and mixtures in disordered microporous matrices prepared by polymerization of species. 

Our main focus in this chapter has been on the applications of the replica Ornstein-Zernike equations designed by Given and Stell [17-19] for quenched-annealed systems. This theory has been shown to yield interesting results for adsorption of a hard sphere fluid mimicking colloidal suspension, for a system of multiple permeable membranes and for a hard sphere fluid in a matrix of chain molecules. Much room remains to explore even simple quenched-annealed models either in the framework of theoretical approaches or by computer simulation. 

S. Murad, J. G. Powles. Computer simulation of osmosis and reverse osmosis in solutions. Chem Phys Lett 225A11, 1994 S. Murad. Molecular dynamics of osmosis and reverse osmosis in solutions. Adsorption 2 95, 1996. 

Garofalini, S.H. (1990) Molecular dynamics computer simulations of silica surface structure and adsorption of water molecules, J. Non-Cryst. Solids, 120, 1. 

This chapter is concerned with the application of liquid state methods to the behavior of polymers at surfaces. The focus is on computer simulation and liquid state theories for the structure of continuous-space or off-lattice models of polymers near surfaces. The first computer simulations of off-lattice models of polymers at surfaces appeared in the late 1980s, and the first theory was reported in 1991. Since then there have been many theoretical and simulation studies on a number of polymer models using a variety of techniques. This chapter does not address or discuss the considerable body of literature on the adsorption of a single chain to a surface, the scaling behavior of polymers confined to narrow spaces, or self-consistent field theories and simulations of lattice models of polymers. The interested reader is instead guided to review articles [9-11] and books [12-15] that cover these topics. 

Nicholson, D. Parsonage, N. G. "Computer Simulation and the Statistical Mechanics of Adsorption" Academic New York, 1982 Chap. 4,6. 

The dependences of pH and C-potential on the adsorbed amount of M(H20)2+ at the total metal ion concentrations of 3 x10-3 mol dm-3 are shown in Figures 7 and 8, respectively. The amount adsorbed for each M2+ increases with the pH, and the inflection points are shifted toward the lower pH region in the order of Co2+, Zn2+, Pb2+, Cu2+, which corresponds to the order of the hydrolysis constant of metal ions. To explain the M2+-adsorption/desorption, Hachiya et al. (16,17) modified the treatment of the computer simulation developed by Davis et al. (4). In this model, M2+ binds coordina-tively to amphoteric surface hydroxyl groups. The equilibrium constants are expressed as... 

An important aspect of the study of water under electrochemical conditions is that one is able to continuously modify the charge on the metal surface and thus apply a well-defined external electric field, which can have a dramatic effect on adsorption and on chemical reactions. Here we briefly discuss the effect of the external electric field on the properties of water at the solution/metal interface obtained from molecular dynamics computer simulations. A general discussion of the theoretical and experi-... 

The main goal of the molecular dynamics computer simulation of ionic solvation and adsorption on a metal surface has been to test the above model and to provide more quantitative information about the different factors that influence the structure of hydrated ions at the interface. Unfortunately, most of the experimental information about these issues has been obtained from indirect measurements such as capacity and current-potential plots, although in recent years in situ experimental techniques have begun to provide an accurate test of the above model. For a recent review of experimental techniques and the theory of ionic adsorption at the water/metal interface, see the excellent paper by Philpott. ... 

In addition to the development of new methods, new applications of molecular dynamics computer simulation are also needed in order to make comparisons with experimental results. In particular, more complicated chemical reactions, beyond the relatively simple electron transfer reaction, could be studied. Examples include the study of chemical adsorption, hydrogen evolution reactions, and chemical modification of the electrode surface. All of the above directions and opportunities promise to keep this area of research very active ... 

EARN distributions the yield along the azimuth 4>= —30° was preferentially reduced with respect to = + 30°. In agreement with intuition, the calculations confirm that the oxygen atom resides in the C-site. Thus from the cooperation of EARN experiments and computer simulations the coverage and nature of the adsorption site of 0/Rh(l 11) has been determined. It will be of interest to see if other surface structure techniques can be used to confirm these s Kcific surface structures. 

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