Mesoporous carbons as adsorbents to removal of methyl orange (anionic dye) and methylene blue (cationic dye) from aqueous solutions

In this study, the removal of methyl orange (MO) and methylene blue (MB) from aqueous solutions using mesoporous carbon materials marked as ST-A and ST-A-CO2 were investigated. The effects of different parameters that affect adsorption process such as contact time, pH, initial dye concentration, and temperature were studied. Removal of methyl orange from acidic solutions was more efficient than from basic solutions. In the case of methylene blue the reverse process was observed. To explain the kinetic model of adsorption, pseudo-first-order kinetic model, pseudo-second-order kinetic model, and the intraparticle diffusion model were used. The experimental data have been described by Langmuir, Langmuir-Freundlich, Freundlich, and Dubinin-Radushkevich adsorption isotherm models. The experimental data were fitted to the pseudo-second- kinetic model and Langmuir isotherm. Results of adsorption experiments showed that the studied carbons are characterized by high adsorption capacity in relation to the methyl orange and the methylene blue. The highest adsorption capacity was obtained for carbon ST-A-CO2 (MO) (330 mg g(-1) in temperature 315 K), lower successively for ST-A-CO2 ( MB) (222 mg g(-1) in temperature 315 K), ST-A (MB) (187 mg g(-1) in temperature 315 K), and ST-A (MO) (154 mg g(-1) in temperature 315 K). Thermodynamic study showed that the adsorption was a spontaneous and endothermic processes (Delta G degrees ranges from -22.60 to -33.08 kJ mol(-1) for all systems tested) and (Delta H degrees is 9.40, 8.12, 3.21, and 7.33 kJ mol(-1) for ST-A (MO), ST-A-CO2 (MO), ST-A (MB), and ST-A-CO2 (MB), respectively).