Removal of toxic dyes from aqueous solutions by adsorption onto a novel activated carbon prepared from chestnut shell

Chestnut shell offers an abundant, renewable and low-cost precursor for the preparation of activated carbon. In this study, a novel activated carbon was prepared from the chestnut shell (CnSAC) by chemical activation with ZnCl2. Based on the N-2 adsorption/desorption isotherm, it is concluded that more micro-pores are developed on the precursor with pore size falls in the range of 0-3 nm. And the X-ray diffraction analysis shows that amorphous carbon and graphite carbon coexist in CnSACs. Moreover, the CnSACs were used to remove methylene blue (MB) from an aqueous solution. Batch adsorption experiments were performed as a function of impregnation mass ratio, impregnation time, activation temperature, activation time and dye solution pH. Besides, the Langmuir, Freundlich and Dubinin-Radushkevich models were applied to describe the equilibrium isotherms. The results showed that equilibrium data fitted well for the Langmuir adsorption isotherms with correlation coefficients of 0.99. The adsorption kinetics of MB were discussed by pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models, which showed that the adsorption followed pseudo-second-order reaction with regard to the intraparticle diffusion rate. Moreover, the maximum adsorption of MB onto CnSACs is 1,489.88 mg/g (impregnation mass ratio: 12.5, impregnation time: 27 h, activation temperature: 600 degrees C, activation time: 75 min, initial MB dye concentration: 600 mg/L). Compared with the ACs prepared from different raw materials, the chestnut shell can be used as a raw material for the preparation of high adsorption performance ACs for the treatment of colored wastewater.