The amount of RhB adsorbed by PK-AC increased along with the increase of contact time. When the contact time exceeded 5 h, the changes of the uptake were very small (Fig. 2), which indicated that the equilibration time was around 5 h. The adsorption capacity of RhB was described by the amount of RhB adsorbed by activated carbon at equilibration time. At the beginning of the adsorption,a large number of active sites (including pore) on the surface of activated carbon were not occupied. Consequently, a rapid adsorption presented at 0–0.5 h. And then, the adsorption slowed down(0.5–6 h) with the decrease of the available adsorption sites, during this process, the RhB molecules had to traverse deeper pores inside the activated carbon and overcome a lager resistance.
With the concentration of RhB increasing (100–600 mg L−1), the adsorption capacity of PK-AC increased from 95.3 to 382.3 mg g−1(Fig. 3a), the removal percentage (the mass ratio of the removed RhBto the initial RhB) decreased from 95.3 to 63.7%. This phenomena can be ascribed to that a high initial concentration of RhB provided necessary driving force for RhB to overcome the mass transfer resistances between aqueous phase and activated carbon, moreover, the competition among the RhB molecules increased with the increase of initial dye concentration.