Preparation of activated carbons by ZnCl2 activation from herb residues under vacuum

Activated carbons were prepared by ZnCl2 activation from herb residues under an absolute pressure of 30 kPa and the Doehlert matrix was used to optimize activation temperature and impregnation ratio based on adsorption capacities of methylene blue and iodine by the activated carbons. Results showed that activation temperature and impregnation ratio had little effect on the total yield of the activated carbons. The activation temperature had a greater influence than the impregnation ratio in methylene blue and iodine adsorption. The optimized activated carbon was obtained under an activation temperature of 474 °C and an impregnation ratio of 1.225, and had a methylene blue value and an iodine value of 316 and 994 mg g−1, respectively. The experimental values agree well with those calculated from the Doehlert model. The activated carbon optimized in this study had a higher adsorption capacity compared with commercial ones.