Bimodal microporous behavior

In all these investigations, very small input amplitudes were used to justify the use of a linear technique for investigation of generally nonlinear adsorption systems. One of the main drawbacks of the classical, linear FR method for investigation of adsorption kinetics is that, in a number of cases, same shapes of linear FR characteristic functions are obtained for different kinetic mechanisms, and the method is reduced to estimation of kinetic parameters of an assumed model. One example of such behavior is the same shape of characteristic curves obtained for adsorption governed by micropore, pore, or pore-siuface diffusion mechanisms [28]. Another very characteristic example is the case of bimodal characteristic functions (with two maxima of the out-of-phase and two inflection points of the in-phase characteristic functions [31,33,35]). These results were shown to fit equally well to three different kinetic models [19,33,35]. As it will be shown in Section III, the nonlinear FR method can overcome this problem. 

---