Comparison of Activated Carbons Prepared from Wheat Straw via ZnCl2 and KOH Activation

Activated carbons were prepared from wheat straw, a wide spread biomass waste in North China, via ZnCl2 and KOH activation. The characteristics of ZnCl2 and KOH activated carbon were compared using N2-adsorption, scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The adsorption behaviors of the activated carbons for the removal of methylene blue (MB) from aqueous solution were investigated, and the MB-saturated activated carbon was regenerated by thermal treatment. The experimental data demonstrated that ZnCl2 activated carbon had a higher surface area and more micropores. Also, the ZnCl2 activated carbon had a more developed aromatic structure. The differences in the characteristics were attributed to the different activation mechanisms of ZnCl2 and KOH. The adsorption equilibrium data of ZnCl2 and KOH activated carbon followed Langmuir isotherm model with the monolayer adsorption capacities of 265.96 and 146.84 mg/g, respectively. Pseudo-second-order kinetic model better described the adsorption kinetic of ZnCl2 activated carbon, and the diffusion mechanism was well described by Weber and Morris intraparticle diffusion model. The MB-saturated ZnCl2 activated carbon can be effectively regenerated by thermal treatment, and the regeneration efficiency was higher than 70 % after five regeneration cycles.