3.2 Adsorption isotherms
The adsorption isotherm is one of the most important approaches to illustrate the mechanism of the adsorption systems. The adsorption isotherms of γ-tocopherol on silica gel were fitted using Langmuir model (Fig. 3a) and Freundlich model (Fig. 3b), respectively. The parameters of Langmuir and Freundlich models were summarized in Table 1.
From Fig. 3a and Fig. 3b, the Langmuir model can be considered as a better model for describing adsorption equilibrium due to its higher correlation coefficient (R2 = 0.9944), followed by the Freundlich model with an R2 value of 0.8997. The value of Qm gives the maximum monolayer adsorption capacity of the adsorbent. In most cases, the constant n of the Freundlich equation shows the adsorption intensity, and the n value between 1 and 10 shows beneficial adsorption (Duran et al. 2011). The n value of the adsorption model was 4.36, which indicated that the adsorption on silica gel (200-300 mesh) can easily take place.