Macroscopic Description of Competitive Adsorption

Transfer of the individual ionic species between the interface and the solution leads to a thermodynamic equilibrium at which the interface is electrically neutral as a whole (and so is the equilibrium bulk solution). 

Based on isothermal reversible work done in transferring one mole of ions of the solute 2 from infinity in vacuum) to a given part in the interfacial region which has a non-zero average charge and where the electrostatic potential is I, it is possible to define the so-called electrochemical potential of component 2 [70] 

According to the surface phase model (cf.. Sect. 6.2.1), when the concentrations of the components of the binary solution ft in the solid phase a are to be neglected, i.e., = 0 (j =1,2), the interfacial concentration F of component j is given by 

The case of 0 defines the preferential adsorption of component j at the Solid-Liquid interface. In a given adsorption system, the interfacial concentration 

When the pure liquid phase is replaced by a binary liquid solution p, the interfacial tensions ysi and ylg will be lowered owing to the preferential adsorption of the solute at the Solid-Liquid and Liquid-Gas interface. The relationship between the extent of adsorption and the resulting interfacial (surface) tension change (T, P = const) is given by the following equation developed by Guggenheim [6, 8] 

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