The Method of Determining Surface Area by Dubinin et al

It is questionable as to whether the various isotherms attributed to Dubinin and coworkers yield the surface area. They are definitely useful for finding the mesoporosity volume due to the clear linear extrapolation. According to Kaganer [16] the intercept of the DR equation is the mono-layer amount. This seems to have been empirically based upon the BET formulation. The modified DR equation, referred to as the DRK equation, for a flat surface is 

A plot of ln(y) versus tl PIP ) yields a plot which is linear over a fair range of values. A typical DRK plot has been presented in Fig. 35. It has been demonstrated [17], according to % theory, that the value of is indeed proportional to the monolayer coverage. One of the problems with this formulation is that both porosity and surface area are dependent upon the intercept value. In other words, there is no way to separate the two physical quantities in this case. Therefore, if one has a sample that is porous and has a significant external area the separation of these two physical quantities is not possible. 

Plot y as function of x and draw the best estimated fit for the portion that is the most linear. This would be roughly through point at the inflection point of the curve and should cover about 2/3 of the plot. 

---