Removal of orange II from aqueous solutions using micro-mesoporous carbon materials: kinetic and equilibrium studies

Adsorption of orange II from aqueous solutions on two carbon materials (ST-A and ST-A-CO2) obtained by the soft-templating method and commercial activated carbon (CWZ 22) was studied. The surface properties of carbons were characterized by nitrogen adsorption isotherms and scanning electron microscopy, the Boehm's titration method and the point of zero charge (pH(PZC)). Investigated adsorbents have specific surface areas from 710 to 950 m(2) g(-1). Adsorption isotherms, adsorption kinetics, the effect of pH solution (2-10) and temperature (298 degrees K, 308 degrees K, and 315 degrees K) on adsorption of orange II on the carbon materials were studied. The experimental data has been described by Langmuir, Langmuir-Freundlich, Freundlich, and Dubinin-Radushkevich adsorption isotherm models. The Langmuir model is the best to describe the received experimental data. Results of adsorption experiments showed that the studied carbons exhibited high adsorption capacity in relation to orange II. The highest adsorption capacity was obtained for carbon ST-A-CO2 (322 mg g(-1)). Maximum adsorption for adsorbents ST-A and CWZ-22 were 127 and 206 mg g(-1), respectively. To explain the kinetic model of adsorption, the pseudo-first-order kinetic model, the pseudo-second-order kinetic model, and the intra-particle diffusion model were used. Adsorption of orange II on all studied carbons runs according to the pseudo-second-order model. The calculated thermodynamic function indicated that the adsorption processes of orange II on all carbon materials were spontaneous and endothermic (Delta H is 22.58, 18.21, and 23.67 kJ mol(-1) for ST-A, ST-A-CO2, and CWZ, respectively).