The Sips isotherm is a combination of the Langmuir and Freundlich isotherms and is given in the following general form:
and may be rearranged to a linear form.
The Sips isotherm has the benefit of reducing to the Freundlich isotherm at low pressures and approaches the monolayer capacity at high pressure similar to the Langmuir isotherm. A Nelder-Mead simplex algorithm may be employed to fit the Sips isotherm model. The Sips isotherm has been added to the advanced reporting system in MicroActive.
Sips, R. (1948) On the structure of a catalyst surface, J. Chem. Phys., 16, 490-495.