The pseudo-first-order and pseudo-second-order kinetic models could not identify the diffusion mechanism. Thus the kinetic
results were then analyzed by using the intraparticle diffusion
model. Weber and Moris plot [25] (qt versus t0.5) was used to investigate intraparticle diffusion mechanism (Fig. 8). If the value of Ci is
zero, then the rate of adsorption is controlled by intraparticle diffusion for the entire adsorption period. However, the plot of qt against
t0.5 usually shows more than one linear portion. As seen from Fig. 8,
the plots were not linear over the whole time range, implying that
more than one process affected the adsorption. A similar behavior
was reported for methylene blue adsorption onto palm kernel fibre
[43].