Determination of the parameters for the 1-pK triple-layer model of ion adsorption onto oxides from known parameter values for the 2-pK TLM.
Prior knowledge of the model parameters describing the metal oxide/simple electrolyte interface is frequently crucial to successful application of surface complexation modeling. On the basis of the parameter values for the 2-pK triple-layer model recently published by Sverjensky, the parameters for the 1-pK TLM were determined. This was done by fitting (using the 1-pK model) the proton surface charge and ion adsorption isotherms generated by the 2-pK TLM. It was assumed that inner-layer capacitance was the same for both models. A strong correlation was found between ion adsorption constants of different electrolytes on the same oxide predicted by both models. Additionally, the 1-pK and 2-pK models predict different electrokinetic potentials in spite of very similar values of calculated surface charge and ion adsorption isotherms when the same value of outer-layer capacitance is assumed. Because the value of outer-layer capacitance practically does not influence surface charge and electrolyte adsorption isotherms, it can be treated as a freely adjusted parameter, the value of which can be estimated if we have measured the electrokinetic potential.
Piasecki
Wojciech
W
Group for Theoretical Problems of Adsorption, Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków, Poland. piach@hermes.umcs.lublin.pl