further increasing the temperature from 303 to 323 K. The above results reflected that the adsorption of RhB onto PK-AC was an endothermic process. The high temperature allowed a bette rmobility of RhB molecules, and was benefit to the adsorption.From Fig. 3c we can see the adsorption capacity increased from 223.8 to 233.9 mg g−1with pH increasing from 1.31 to 3.20. The changes of adsorption capacity were small within the pH range of 3.20–10.19. When the pH was changed from 10.19 to 13.56,the adsorption capacity decreased from 232.4 to 217.7 mg g−1. The effect of initial solution pH on RhB adsorption was a complex pro-cess. Largura et al. reported that the adsorption of RhB increased as the pH increased due to the existence of electrostatic interaction between negatively charged surface of the adsorbent and RhB[14]. Jain et al. presented a different result, the adsorption of RhB decreased with increasing pH, the explanation of this result wasthat a low pH increased protonation of adsorbent, this contributedto the diffusion of RhB and generated a great deal of active siteson the surface of adsorbents [15]. Wang and Zhu demonstrated thepH exerted a little effect on RhB adsorption, this phenomenon wascaused by the presence of different functional group on RhB [16].In addition, RhB can exhibit different molecular forms in different pH solution, it is a monomeric form below pH = 3.5, a zwitterionic form above pH = 3.5 [17]. H+ion may compete with cation in RhB solution, and OH−may compete with the anion. Besides the form ofRhB molecular, pH also influences the surface charges on the activesites of activated carbon. Considering the above-mentioned factors,it is not surprising that the changing tendency of adsorption capac-ity was irregular. Here, the adsorption capacity changed with the variation of pH, but these changes were small. The pH point of zerocharge of PK-AC was 6.48 (Fig. 4) that was close to neutral, indi-cating the number of the surface acid functional groups and basic functional groups of PK-AC may be approximately equal. The pH had little effect on the adsorption of RhB onto PK-AC. PK-AC showed good adsorption properties both in acidic and alkaline solutions.This result illustrated that PK-AC will be a good adsorbent.