Adsorption and Desorption of Phenol onto Granular Activated Carbon: Kinetics and Thermodynamic Studies

Modelization of adsorption and desorption of phenol from granular activated carbon (GAC) by organic solvent acetone and green solvent limonene and then by mixture of both solvents is investigated in this paper. The results showed that the pseudo-second-order kinetic model more appropriately described the phenol adsorption and desorption. The adsorption isotherms at 20, 30, and 40 °C indicated that the Langmuir model better expressed adsorption, while desorption isotherms revealed that desorption is well fitted by Freundlich model. Following adsorption isotherms, the surface occupied with phenol could be calculated indicating that not the whole surface was covered with phenol molecules due to the acidic surface. The negative ΔH° showed that adsorption (− 0.0144 kJ·mol⁻¹) and desorption (acetone: − 0.0179 kJ·mol⁻¹ limonene: − 0.0174 kJ·mol⁻¹) were exothermic processes. In addition, the negative ΔS° showed that adsorption (− 0.0178 kJ·mol⁻¹·K⁻¹) implies the non-affinity of the surface for phenol; however, the positive ΔS° in desorption (acetone: 0.0157 kJ·mol⁻¹·K⁻¹ limonene: 0.0182 kJ·mol⁻¹·K⁻¹) means an affinity between adsorbent surface and adsorbate. The negative values of free energy ΔG° obtained for adsorption and desorption indicate the feasibility and spontaneous nature of adsorption and desorption process.