Hi, I have done a series of adsorption isotherm experiments.
when I fitted my data with sips isotherm, the value of "as" constant became negative.
qe=(Ks*Ce^βs)/(1+ as*Ce^βs)
Does it have any meaning?
is it possible?
I saw that in the linear form of sips isotherm the constant as is in logarithm. so, is it possible? or they are irrelevant to each other.
βs*ln(Ce)= -ln(Ks/qs)+ ln(as)
Hello.
You can use this expression:
Qe=(Qs*Ks*Ce^(1/n))/(1+Ks*Ce^(1/n))
It only means that you cannot use the Langmuir-Freundlich isotherm (instead of Ks it should be qmas) to desribe your equilibrium data or you have misused the graphical method.
Thank you dear Mirosław Grzesik , I think so. I think this model is not appropriate for my data. Do you know any reference that exactly indicate to this matter?
dear Otheman Amrhar thanks for your reply. of course it can be checked with other form of the equation. But I wanted to know the possibility of negative as and also the reference, you might know, that exactly indicate its possible range.
Zahra Mousavi, Use the correct form of the Langmuir-Freundlich (Sips) isoherm. Use the nonlinear regression method to determine the parameter values, not the graphical method. I don't think you would then get the negative value of the equilibrium constant, as. Let me add that your second equation, implicit with respect to qe and Ce, is also incorrect.