Effects of pyrolysis temperature and impregnation ratio on adsorption kinetics and isotherm of methylene blue on corn cobs activated carbons

•Corncob-derived activated carbon (CAC) is synthesised based on chemical impregnation and pyrolysis.•Impregnation ratio (IR) of 4.5:1 is optimum in resulting enhanced kinetics•Pseudo second order model can describe well the adsorption kinetics•Freundlich isotherm well represents the multilayer adsorption of methylene blue onto CAC The rapid development of textile industries in developing countries has resulted in enormous dye waste, which remains problematic in some areas due to the lack of advanced technology. Adsorption appears as an efficient method for treating dye waste, which often relates to the use of conventional activated carbons produced from non-renewable sources such as coal. On the other hand, biomass is greatly available in developing countries and represents as a cheaper carbon source in the production of activated carbon for dye waste treatment. This research addresses the potential of corn cobs as the raw material of activated carbon, where the synthesis of corn cob-derived activated carbon consists of chemical impregnation by phosphoric acid into corn cobs followed by the pyrolysis process at varied impregnation ratios and temperatures. The experiment showed that the development of pores was enhanced by increasing the pyrolysis temperature but heating beyond 550 °C may cause the pores to collapse. Besides, the optimum impregnation ratio was found to be 4.5:1 as the adsorption kinetics ceased to improve at higher ratio. In addition, the adsorption kinetics were well represented by the pseudo-second-order kinetics model, whereas further investigation revealed that intra-particle step existed but did not control the adsorption process. Moreover, multilayer adsorption is implied by the good agreement of the adsorption data with the Freundlich isotherm.