The amount of RhB adsorbed by PK-AC increased along with theincrease of contact time. When the contact time exceeded 5 h, thechanges of the uptake were very small (Fig. 2), which indicated thatthe equilibration time was around 5 h. The adsorption capacity ofRhB was described by the amount of RhB adsorbed by activatedcarbon at equilibration time. At the beginning of the adsorption,a large number of active sites (including pore) on the surface ofactivated carbon were not occupied. Consequently, a rapid adsorp-tion presented at 0–0.5 h. And then, the adsorption slowed down(0.5–6 h) with the decrease of the available adsorption sites, duringthis process, the RhB molecules had to traverse deeper pores insidethe activated carbon and overcome a lager resistance.With the concentration of RhB increasing (100–600 mg L−1), theadsorption 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 phenomenacan be ascribed to that a high initial concentration of RhB providednecessary driving force for RhB to overcome the mass transfer resis-tances between aqueous phase and activated carbon, moreover, thecompetition among the RhB molecules increased with the increaseof initial dye concentration.