Equilibrium Adsorption Studies of Methylene Blue onto Caesalpinia pulcherrima Husk-based Activated Carbon

Abstract

Activated carbon was prepared from Caesalpinia pulcherrima husk (CPH) by chemical activation method using phosphoric acid as an activating agent.  The activated sample was characterized based on the physical properties.  The experimental data were fitted to Langmuir, Freundlich and Temkin models. The coefficient of determination for Langmuir model R2 = 0.967 was higher compared to Freundlich and Temkin showing monolayer adsorption, and also established that the adsorption of methylene onto CPH based activated carbon can be best described by the Langmuir isotherm model. The energy of adsorption (806.2 kJ/mol) obtained from this model shows clearly that the process is chemisorption. It was observed that the adsorption characteristic indicates a rapid uptake of the adsorbate; the optimum contact time for the adsorption of Methylene blue onto the prepared carbon was 60 minutes. This evidence also points to chemisorption process. These results demonstrate that the carbon derived from CPH can be used as an efficient adsorbent for the adsorption of Methylene blue.