Kinetics and isotherm evaluation for adsorptive removal of anionic and cationic dyes from aqueous media by sulfuric acid-modified beech sawdust

Abstract

A novel and efficient adsorbent was prepared by modifying Fagus orientalis L. (beech) sawdust with H2SO4. The adsorption behavior of H2SO4-modified beech sawdust (SMBS) was investigated by batch experiments to offer a straightforward, inexpensive, and effective method for the retention of anionic and cationic model dyes, indigo carmine (IC) and methylene blue (MB), from wastewater. The experimental conditions were optimized by investigating the effects of the initial pH, initial concentrations of IC and MB dyes, dosage of SMBS, period of the contact, and the presence of salts in the aqueous media on the adsorptive performance of SMBS. The initial pH values of the aqueous solutions, from which IC and MB dyes will be removed, were optimized as 2.0 and 6.5 (natural), respectively. The optimum contact time for the adsorption of both dyes onto SMBS was determined to be 240 min. The mechanisms in the adsorption of IC and MB onto SMBS were investigated by evaluating the experimental data through different isotherm and kinetic models. The Langmuir isotherm model and pseudo-second order kinetic model performed well in explaining the mechanism of adsorption. Langmuir monolayer adsorption capacity of SMBS adsorbent was 38.85 mg g−1 for IC and 58.82 mg g−1 for MB. As a result, CMCP exhibited excellent performance in adsorbing organic pollutants, providing a low-cost and easily prepared alternative to other adsorbents found in the literature.