Dye adsorption on a heterogeneous surface is assumed not to be restricted to a monomolecular layer, leading to the proposed Freundlich model (Balarak et al. 2015). The Freundlich equation was used to examine equilibrium data for MR adsorption onto AC from orange peels. The straight line with an intercept of ln KF and a slope of 1/n can be seen in the plot of ln qe vs. ln Ce which is shown in Figure 11. The Freundlich model correlation coefficients (R2) suggest that experimental data fitted to the model, and n > 1 indicates that dye adsorption onto orange peel AC is a favorable adsorption process. When compared with the Langmuir isotherm models, the R2 value suggests that the Freundlich isotherm is less relevant. Table 3 shows the Freundlich isotherm constants.
Table 3

Freundlich isotherm constants

Temperature (°C)ConstantsMagnitude
60 °C KF (mg g−1) (mg3/g)1/n 8.07 
n 1.96 
R2 0.966 
Temperature (°C)ConstantsMagnitude
60 °C KF (mg g−1) (mg3/g)1/n 8.07 
n 1.96 
R2 0.966 
Figure 11

Freundlich isotherm at 60 °C, 11 pH, 100 ppm, 1 g/L orange peels AC.

Figure 11

Freundlich isotherm at 60 °C, 11 pH, 100 ppm, 1 g/L orange peels AC.

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