understanding of the adsorption behavior and the heterogeneity
of the adsorbent surface. The Langmuir equation can be
represented as follows [28]:
qe ¼
QmaxKLCe
1þKLCe
ð1Þ
where: Ce (mmol/dm3) is the equilibrium concentration of dye
in solution; qe (mmol/g) is the surface concentration of dye at
equilibrium; Qmax (mmol/g) is the amount of dye adsorbed at
complete monolayer coverage; KL (dm3/mmol) is a constant
that relates to the heat of adsorption [24].
The Freundlich model can take the following form [28]:
qe ¼ KFCn
e ð2Þ
where: KF [mmol/g (mmol/dm3)n] represents the adsorption
capacity when dye equilibrium concentration (Ce) equals 1;
n represents the degree of dependence of adsorption on equilibrium
concentration. The model parameters (as obtained
from linear-regression analysis) and correlation coefficients
(r2) are presented in Table 4.
3.3.1.1. Langmuir model. The correlation of the dye adsorption
data with the Langmuir isotherm model was high, with
r2 values of 0.9912, 0.9712 and 0.9735 for C.I. Reactive Blue
2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes, respectively.
As shown in Table 4, the maximum adsorption values for
the dyes were 0.27 and 0.24 and 0.11 mmol/g for C.I. Reactive
Blue 2, C.I. Reactive Yellow 2, and C.I. Reactive Red 4, respectively.
KL represents the equilibrium adsorption constant, therefore
higher values of KL were indicative of a favorable
adsorption process. By comparing the values of KL, it can be