3.5. Adsorption kineticsAdsorption kinetics of RhB, including the adsorption mechanismand rate controlling steps, were examined by pseudo-first order,pseudo-second order and intra-particle diffusion model.3.5.1. Pseudo-first order modelThe pseudo-first order model [18] is depicted as:
log(qe −
qt )
=
log qe − k1t
2.303
(2)where qe(mg g−1) and qt(mg g−1) are the adsorption capacityof RhB onto PK-AC at equilibrium and at time t, respectively. k1(min−1) is the pseudo-first order rate constant. The values of k1andqe, obtained from the slop and the intercept of plots of log(qe− qt)versus t, are displayed in Table 2.