Specific surface area negative adsorption methods

The development of a negative adsorption method for measuring specific surface area is based on the additional definition ... 

The determination of specific surface area of soils and soil coUoids is of great importance in characterizing the reactivity of a sample, among other factors. However, it is actually an operational concept, because the A5 value depends on the experimental method employed, as it will be shown in Section 7.6.4.I. The underlying fact is that the effective area available for a particular reaction or process is dependent on the reactants and/or external factors involved. The experimental methods can be broadly classified into three categories (Sposito 1984) physical methods, positive adsorption methods, and negative adsorption methods. 

Apart from the original method mentioned above, Morrison and eo-workers [143,144] formulated a new iterative teehnique ealled CAEDMON (Computed Adsorption Energy Distribution in the Monolayer) for the evaluation of the energy distribution from adsorption data without any a priori assumption about the shape of this function. In this case, the local adsorption is calculated numerically from the two-dimensional virial equation. The problem is to find a discrete distribution function that gives the best agreement between the experimental data and calculated isotherms. In this order, the optimization procedure devised for the solution of non-negative constrained least-squares problems is used [145]. The CAEDMON algorithm was applied to evaluate x(fi) for several adsorption systems [137,140,146,147]. Wesson et al. [147] used this procedure to estimate the specific surface area of adsorbents. 

The solution depletion method for studies of adsorption in solution uses material in the form of powder or pellets with specific dimensions and surface areas. This material may be physically or chemically treated to produce hydrophobic, or positively or negatively charged hydrophilic surfaces which is exposed to the solution. The decrease in concentration of the adsorbate from the bulk solution is then measured. The precision of this method is dependent on the analytical technique used. However, for biological material, the technique does not allow measurement of subtle changes in surface denaturation. The technique has been used by a number of researchers. ... 

---