Adsorption of Caffeine on Activated Carbon Obtained from Green Coconut Waste

Abstract

In this study activated carbon was produced using green coconut shell as the carbon source. Furthermore, caffeine adsorption behavior in the produced material was studied, as a function of temperature, through the adsorption isotherms and their thermodynamic parameters. For this, the green coconut shell powder was subjected to the activation process, involving impregnation with phosphoric acid solution followed by pyrolysis in a muffle furnace. The adsorption experiments at four temperatures, 25, 35, 45 and 55°C, were studied with five aqueous solutions of different caffeine concentrations maintaining the same agitation rate (150 rpm). Langmuir and Freundlich equations were employed for thermodynamic equilibrium, the data adjusting better to the Langmuir model. The thermodynamic parameters such as entropy change, enthalpy change and Gibbs free energy variation were calculated from the linear equation of the Van’t Hoff. The results showed that caffeine adsorption in the activated carbon is a spontaneous and exothermic process, and the amount of caffeine adsorbed increases according to the concentration at a constant temperature, reaching values close to 170 mg g-1. The results demonstrated the potential of green coconut waste material as feedstock to obtain activated carbon, as well as for the treatment of wastewater containing emerging contaminants.