Adsorption on charged surfaces

Westall, J., 1980, Chemical equilibrium including adsorption on charged surfaces. In M. C. Kavanaugh and J. O. Leckie (eds.), Advances in Chemistry Series 189, American Chemical Society, Washington, DC, pp. 33 14. 

It is important to concentrate special attention on the first step of the process, viz on the study of polyelectrolyte adsorption on charged surface. The time dependence of layer growing and structural reconstruction can give the information of formation mechanism of the multilayer. 

Schwarz S, Buchhammer H-M, Lunkwitz K, Jacobasch HJ (1998) Polyelectrolyte adsorption on charged surfaces study by electrokinetic measurements. Colloids Surf A Physicochem Eng Aspects... 

Westall, J. C. 1980. Chemical equilibrium including adsorption on charged surfaces. Adv. Chem. Ser. 189 33-44. 

Chemical Equilibrium Including Adsorption on Charged Surfaces... 

Tnterest in the fate of chemical substances in the aquatic environment has stimulated research in many areas, including the adsorption of materials on hydrolyzable metal oxide surfaces. Quantitative interpretation of adsorption on these surfaces is complicated because the electrostatic energy of adsorption is variable, and often a large number of chemical species are present in solution and adsorbed to the surface. In this chapter a chemical equilibrium approach is used to interpret adsorption on charged surfaces. 

The basis for the discussion of adsorption on charged surfaces is the surface complexation model. The precept for this model is the use of the standard mass-action and mass-balance equations from solution chemistry to describe the formation of surface complexes. Use of these equations results in a Langmuir isotherm for the saturation of the surface with adsorbed species. There are of course other models that satisfy these precepts, but which are not generally referred to as surface complexation models, for example, the Stern model (J). 

While there are similar mass-balance and mass-action equations in all surface complexation models, there are a great number of ways to formulate the electrostatic energy associated with adsorption on charged surfaces. Customarily the electrostatic energy of an adsorbed ion of formal charge 2 at a plane of potential is taken by Coulomb s law to be zFt/r, but the relationships used to define surface potential t/r as a function of surface charge a, or any other experimentally observable variable, are different. In addition, different descriptions of the surface/solution interface have been used, that is, division of the interface into different layers, or planes, to which different ions are assigned formally. 

The method developed here for the description of chemical equilibria including adsorption on charged surfaces was applied to interpret phosphate adsorption on iron oxide (9), and to study electrical double-layer properties in simple electrolytes (6), and adsorption of metal ions on iron oxide (10). The mathematical formulation was combined with a procedure for determining constants from experimental data in a comparison of four different models for the surface/solution interface a constant-capacitance double-layer model, a diffuse double-layer model, the triplelayer model described here, and the Stem model (11). The reader is referred to the Literature Cited for an elaboration on the applications. 

The concept of inner-sphere surface complexation as the basis for relative metal adsorption selectivity in soils was introduced in W. R. Heald, M. H. Frere, and C. T. deWit, Ion adsorption on charged surfaces. Soil Sci. Soc. Am. J. 28 622 (1964). Further quantitative development of this concept was given in... 

We have also discussed two applications of the extended ab initio atomistic thermodynamics approach. The first example is the potential-induced lifting of Au(lOO) surface reconstmction, where we have focused on the electronic effects arising from the potential-dependent surface excess charge. We have found that these are already sufficient to cause lifting of the Au(lOO) surface reconstruction, but contributions from specific electrolyte ion adsorption might also play a role. With the second example, the electro-oxidation of a platinum electrode, we have discussed a system where specific adsorption on the surface changes the surface structure and composition as the electrode potential is varied. 

The effects of organic molecules and phosphate on the adsorption of acid phosphatase on various minerals, and kaolinite in particular, have been investigated by Huang et al. [97]. The Langmuir affinity constant for AcP adsorption by kaolinite follows the series tartrate (K — 97.8) > phosphate (K= 48.6) > oxalate (K — 35.6) > acetate (K= 13.4). At low concentration, acetate even promoted the adsorption of acid phosphatase. It was considered that competitive interactions between anionic adsorbates can occur directly through competition for surface sites and indirectly through effects of anion adsorption on the surface charge and protonation. 

Kampf N, Scheinost AC, Schultze DG (2000) Oxides minerals. In Sumner ME (ed) Handbook of soil science, CRC Press, Boca Raton (FL), F125-F168 Jain A, Loeppert RH (2000) Effect of competing anions on the adsorption of arsenate and arsenite by ferrihydrite. J Environ Qual 29 1422-1430 Jain A, Raven KP, Loeppert RH (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH release stoichiometry. Environ Sci Technol 33 1179-1184... 

Decher G, Hong JD. Buildup of ultrathin multilayer films by a self-assembly process. 1. Consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces. Makromolekulare Chemie-Macromolecular Symposia 1991a 46 321-327. 

Coulombic attraction between charged species in solntion and a snrface may play a part in initial adsorption on the surface. Under the high pH valnes more com-... 

Jain, A., Raven, K.P. and Foeppert, R.H. (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH - release stoichiometry. Environmental Science and Technology, 33(8), 1179-84. 

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