Surface Model Assumptions

During the protonation, or dissociation, of the surface OH groups either a negative or a positive surface potential is generated, depending on the pH and on the ionic strength of the liquid phase. Therefore, the respective counterions are subject to an attraction while the co-ions are rejected. Due to the sorption of counterions at functional groups, the surface potential is partly decreased. Unlike the description widely used in the literature, it is assumed that each kind of counterion is located at a characteristic distance from the surface. Thus, ordered double or 'Stern' layers are formed. Ion pairs between surface groups and counterions in the ordered layer are designated as surface complexes. Excess charges at the surface are balanced by counterions in the diffuse layer, which also contains co-ions. As a consequence, the surface potential continuously decreases normal to the surface to zero in the liquid phase. The equilibrium between solid and liquid phases is mainly dominated by protolytic reactions. In this way, the protons are the potential-determining species.

For a system with Cl" and Na + ions the schematic arrangement of counterions and co-ions and the corresponding development of the potential are plotted in Figure 1. With respect to the radii of the hydrated species, the anion layers are assumed to be closer to the surface than those of the cations. (Cl" and Na + ions are used as model counterions. Individual properties are not taken into account. Furthermore, the absolute values of the potential in the different layers are of no importance for the further mathematical derivations.)

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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