Specific adsorption, role surface charge

Also the choice of the electrostatic model for the interpretation of primary surface charging plays a key role in the modeling of specific adsorption. It is generally believed that the specific adsorption occurs at the distance from the surface shorter than the closest approach of the ions of inert electrolyte. In this respect only the electric potential in the inner part of the interfacial region is used in the modeling of specific adsorption. The surface potential can be estimated from Nernst equation, but this approach was seldom used In studies of specific adsorption. Diffuse layer model offers one well defined electrostatic position for specific adsorption, namely the surface potential calculated in this model can be used as the potential experienced by specifically adsorbed ions. The Stern model and TLM offer two different electrostatic positions each, namely, the specific adsorption of ions can be assumed to occur at the surface or in the -plane. 

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. 

Hohl, H., L. Sigg, and W. Stumm (1980), "Characterization of Surface Chemical Properties of Oxides in Natural Waters The Role of Specific Adsorption Determining the Specific Charge," in M. C. Kavanaugh and J. O. Leckie, Eds., Particulates in Water, Advances in Chemistry Series, ACS 189, 1-31. 

The Role of Specific Adsorption in Determining the Surface Charge... 

Apart from chemisorption, the state of reconstruction of a surface may be affected by an electric potential across the surface/ solution interface in an electrochemical system [28]. It was found that at electrode potentials positive to the potential of zero charge, the reconstruction is lifted and the surface changes to the bulk-truncated structure. Thus, the hex structure of a Au(l 00) electrode is lifted in 0.01 M HCIO4 solution at E> 0.60 V versus saturated calomel electrode, SCE, but already at E > 0.27 V versus SCE in 0.01 M H2SO4 solution, indicating the additional role of specific adsorption. These findings could recently be surprisingly well reproduced theoretically by a combination of DFT and thermodynamic considerations [30]. 

The UPD takes place at a surface (in a potential range) where the role of the specific adsorption of anions can be neglected. In such cases the mass and charge balance can be relatively easily treated. 

We have little direct in situ (microscopic) information on the specific adsorption of charged species (ions) at the oxide/aqueous solution interface in strong acid media despite the fact that the role of the surface chemistry of the metal (hydr)oxide/solution interface is well documented [12, 13, 14, 15, 16]. 

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