A kinetic, equilibrium and thermodynamic study of l-phenylalanine adsorption using activated carbon based on agricultural waste (date stones)

The main purpose of this work is to produce low cost activated carbons from date stones wastes for the adsorption of l-phenylalanine. The activated carbons were prepared by chemical activation with KOH (ACK) and ZnCl2 (ACZ) and characterized by scanning electron microscopy, N2 adsorption-desorption isotherms and FT-IR spectroscopy. Both The activated carbons ACK and ACZ have high specific surface areas and large pore volumes, favorable for the adsorption. Batch experiments were conducted to determine the adsorption capacities. A Strong dependence of the adsorption capacity on pH was observed, the capacity decreases with increasing pH up to optimal value of 5.7. The adsorption follows a pseudo-second order kinetic model. Additionally, the equilibrium adsorption data were well fitted to the Langmuir isotherm, and the maximum adsorption capacities of l-phenylalanine onto ACK and ACZ were 188.3 and 133.3 mg g−1 at pH 5.7, respectively. The thermodynamic study revealed that the adsorption of l-phenylalanine onto activated carbons was exothermic in nature. The proposed adsorption mechanisms take into account the hydrophobic and electrostatic interactions which played the critical roles in the l-phenylalanine adsorption.