approximately 4.5 h was sufficient to reach equilibrium. The highest qe value (232 mg g 1) was observed in the 60 C experiment for
the initial MB concentration of 900 mg L1, showing that the equilibrium adsorption capacity was positively affected by temperature. Such endothermic nature of the process may be due to the
fact that high temperatures increase the free volume in the adsorbent pores due to increased movement of the solute [28,29].
Adsorption isotherms show how solutes interact with adsorbents and so are critical in optimizing the use of adsorbents. Thus,
the correlation of equilibrium data by either theoretical or empirical equations is essential to the practical design and operation of
sorption systems [30]. Linearization of Langmuir isotherm (Eq.
(2)) is frequently used to determine the best-fitting parameters
[21,31].
C
e
qe
¼
1K
L
þ
aL
KL Ce ð2 Þ
By plotting Ce/qe against Ce, it is possible to obtain the value of KL
from the intercept (1/KL) and aL from the slope (aL/KL). The corresponding plots and values are shown in Fig. 4 and Table 1 , respec