Preparation and Characterization of Activated Carbon from Rice Straw Pre-treated by the Subcritical Hydrolysis

Activated carbons were prepared from waste residue which was obtained from rice straw dealt with subcritical water by chemical activation with ZnCl2.It was also considered that the variations of activation temperature,activation time,impregnation time and impregnation ratio influenced the performance of activated carbon.Adsorption isotherm and scanning electron microscopy(SEM) were used to characterize the pore structure and surface morphology of carbon.Adsorption kinetics and isotherms of methylene blue,used here as a reference compound,were studied.The results show that when zinc chloride content was 20%,the optimum conditions of activated carbon produced are obtained-reaction temperatures of 900℃,activation time of 60 min,impregnation ratio of 1∶5 and impregnation time of 12 h.The number of iodine and methylene blue of activated carbon is 1 122.79 mg·g-1,136.50 mg·g-1,respectively.Adsorption of methylene blue on activated carbon fits the Langmuir equation and pseudo-second kinetic model can well describe the adsorption process of methylene blue.The negative change in free energy(ΔG0) and positive change in enthalpy(ΔH0) indicate that the adsorption is a spontaneous and endothermic process.