2. Experimental
2.1. Production of activated carbonsRice husk was obtained from local farmer near Changchun. Therice husk was mixed 2.2. Adsorption procedureThe sorption of RhB was performed by batch technique. Theamount of each adsorbent was fixed at 0.02 g, and the volume ofRhB solution was fixed at 20 mL. According to the calibration curveof RhB, the max= 554 nm. The initial concentration of RhB solu-tion was from 100 to 600 mg L−1, the adsorption was carried out at293–323 K for 0.5–6 h. pH was adjusted by 0.1 M HCl or 0.1 M NaOH(the addition of acid or alkali in RhB solution was carried out whenwe investigated the effect of pH on adsorption). The amount of RhBadsorbed at time t (qt) was calculated by the equation:
qt = V(C0 −
Ct )
m
(1)where C0(mg L−1) was the initial concentration of RhB, Ct(mg L−1)was the concentration of RhB at time t, V (L) was the volume of theRhB solution, m (g) was the mass of the activated carbon.2.3. Point zero chargeThe pH point zero of charge was the pH value of the solution sur-rounding the adsorbent when the sum of surface positive chargeswas equal to the sum of surface negative charges [10]. The pointzero charge of PK-AC was obtained by the solid addition methodaccording to the report in the literature [11].