Equilibrium, thermodynamic and kinetic studies on adsorption of shikimic acid onto activated carbons

The properties of adsorption of shikimic acid by activated carbons were investigated in batch experiments. The adsorption of shikimic acid was strongly influenced by temperature. The Freundlich and Langmuir models were used to fit experimental data. The results of regression showed that the Freundlich equation was more suitable. Some thermodynamic parameters were calculated. The changes in enthalpy for both adsorbents were negative and the absolute values were lower than 40 kJ/mol, which indicated that the adsorption process was exothermic and mainly physical. The changes in Gibbs free energy for both adsorbents were negative, which indicated that the adsorption occurred spontaneously. And the adsorption process increased the degree of freedom; the entropy shows the positive value. The kinetic parameters showed that the adsorption of shikimic acid onto activated carbons was controlled mainly by pseudo-second-order equation. As increasing initial concentration of shikimic acid, the adsorption rate constant decreased while the maximum adsorption capacity increased.