Based on the R2 values obtained, the goodness-of-fit of experimental
data to the predicted values (isotherm models) are according
to the following order; Langmuir > RedlichPeterson
> Freundlich. It is therefore postulated that the adsorption
of methylene blue takes place at a specific homogenous sites on the
surface of adsorbent (PLAC-B) where each molecule possessing
constant enthalpies and sorption activation energy. All binding
sites also possess equal affinity for the adsorbate, with no transmigration
of the adsorbate in the plane of the surface (Kundu and
Gupta, 2006; Perez-Marín et al., 2007 ). This shows that the
adsorption occurs at finite (fixed) number of definite localized sites,
which are identical and equivalent with no lateral interaction and
steric hindrance between the adsorbed molecules and the adjacent
sites (Foo and Hameed, 2010). Table 4 highlights the comparison
between PLAC-B and other adsorbents on the removal of methylene
blue.
Table 4 indicates the potential of using pineapple leavesactivated
carbon (PLAC-B) to effectively remove methylene blue
from solution. Maximum methylene blue removal capacity of
288 mg/g recorded in this work is higher compared to the other
adsorbents listed except for date stones (398 mg/g). Moreover,
PLAC-B demonstrates a greater removal of methylene blue than
activated carbons with higher surface area. From the KL value of
0.075, the separation factor (RL) was determined using the
following equation (Prahas et al., 2008),