Effect of Modification of Activated Carbon on the Removal of Methylene Blue from Aqueous Solutions

The structural-sorption and surface properties of activated carbon from apricot pits (KAU) and of its modified sample KAU-Fe obtained by treatment with iron salts are investigated. Modification of KAU leads to an increase in the total specific surface area by 10.0%, in the mesopore surface by 17.8%, in the micropore surface by 17.6%, in the volume of the total pore space by 14.3%, and in the volume of micropores by 19.3%. An increase in the values of cationic and anionic static exchange capacities is noted. Adsorption isotherms of the cationic dye Methylene Blue have been obtained at temperatures of 283, 293, and 313 K. The increase in the adsorption value of Methylene Blue on KAU-Fe relative to the values for unmodified carbon is 40.4% at a temperature of 283 K; 72.4% at a temperature of 293 K; and 54.3% at a temperature of 313 K. The obtained results are described, using the Langmuir, Freundlich, Temkin, BET, and Dubinin−Radushkevich models. It is shown that the adsorption process of Methylene Blue proceeds according to a physical mechanism. Modeling of the kinetics of Methylene Blue adsorption on activated carbons is performed by the pseudo-first order, the pseudo-second order, the Elovich, and the Morris−Weber equations. It is revealed that the adsorption process of Methylene Blue proceeds in a mixed diffusion mode. Negative values of the change in Gibbs free energy indicate the spontaneous adsorption of Methylene Blue by the studied carbon. A positive value of enthalpy testifies to an endothermic course of the adsorption process; and positive entropy indicates that surface changes are related to the interaction of Methylene Blue molecules with active centers of adsorbents.