Asymptotic Cases of Langmuir Photoadsorption Isotherm

A straightforward determirtation of Kl, Ng, k, and Cl,o parameters can be done in the following way. k and Cl.o niay be easily determined by considering two asymptotic situations of Langmuir adsorption isotherm, that is, very high or very low substrate concentration. At very high concentrations of substrate the following inequality may be assumed to hold  

The total disappearance rate of substrate per unit surface area, rx, gets of zero order so that Equation (15) can be written as  

Taking the derivative of Equation (A3) with respect to time, it yields that dCx/df = dCL/df. Substituting this equality in Equation (A4) and rearranging, one obtains 

Integration of Equation (A5) with the condition that Cl = Cl,o for f = 0 yields the following relationship  

At very low concentrations of substrate, the following inequality may be assumed to hold  

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