3.2.5 Study of isothermal absorption models
In this study, to evaluate the isotherms of adsorption on the desired
adsorbent under optimal conditions, the three absorption isotherms of
Langmuir, Freundlich and Tamkin were examined (Fig. 9).
Fig. (9): Investigation of adsorption isotherms, a) Langmuir isotherm b)
Freundlich isotherm c) Temkin isotherm.
In isothermal absorption, it is assumed that the drug is placed on the
adsorbent as a single-layer coating. According to the calculation, the
R2 obtained from the isotherm is the absorption of
Langmuir (0.948), which indicates that there is a single molecular
absorption of curcumin on the target adsorbent. Freundlich adsorption
isotherm is widely used for multilayer absorption modeling on
heterogeneous adsorbent surfaces and it is not limited to the formation
of a single layer on the surface in addition absorption functions can
also be described using the Freundlich isotherm parameters. As can be
seen from the calculations, R2 is obtained from the
calculations of this isotherm (0.995). Also, the value (1/n) obtained
indicates that the adsorption conditions of curcumin on the adsorbent
are optimal and the curcumin groups are adsorbed on the heterogeneous
adsorbent surface. Using the Temkin adsorption isotherm, the ratio of
the surface covered to the total available surface can be obtained for
the adsorbent and in this isotherm, R2 is equal to
(0.945). This indicates that almost a large area of the adsorbent is
available to absorb curcumin and is covered with curcumin.
Table (7): Investigation of different types of isotherms of absorption
and presentation of their parameters