Isotherm, Kinetic, and Thermodynamic Characteristics for Adsorption of 2,5-Xylenol onto Activated Carbon

The adsorption of the major tar compound, 2,5-xylenol, derived from the plant cell cultures of Taxus chinensis, onto activated carbon was examined at different initial 2,5-xylenol concentrations, durations, and temperatures. From the analysis of adsorption isotherms, the Langmuir isotherm model showed good fit to the equilibrium adsorption data. It was found that adsorption capacity decreased with increasing temperature, and the adsorption of 2,5-xylenol onto activated carbon was favorable. The obtained kinetic data for 2,5-xylenol adsorption with activated carbon agreed well with the pseudo-second-order kinetic model. By using intraparticle diffusion model, intraparticle diffusion and boundary layer diffusion did not play a dominant role in 2,5-xylenol adsorption. Thermodynamic parameters were calculated, which indicated that the adsorption was non-spontaneous, irreversible and exothermic nature. The isosteric heat of adsorption decreased with increase in surface loading, indicating a heterogeneous surface.