Removal Of Methylene Blue From Aqueous Solution Using Coffee Husk Activated Carbon

Abstract

In this study coffee husk activated carbon (CHAC) was prepared and utilized as adsorbent to study its adsorption efficiency towards removal of methylene blue dye from aqueous solution. Activated carbon was prepared by acid treatment and carbonized at 500oC for an hour. The amount of MB dye adsorbed was determined using UV-Vis spectrophotometer at its λ max of 663 nm. It was found that the adsorption of MB on the CHAC obeys both the Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity (‘Qe’) and energy of adsorption (‘b’) were found to be 8.55 mg/L and 0.55 L/g, respectively as calculated from the Langmuir isotherm model. Values of the equilibrium parameter ‘RL’ from the Langmuir isotherm range between 0.022-0.083. Likewise the adsorption capacity of the adsorbent (‘Kf’) and the adsorption intensity (’n’) were determined from the Freundlich isotherm and found to be 4.91 mg/g and 7.30, respectively. These results confirmed that the adsorption process of MB dye on the prepared adsorbent (CHAC) is favorable. The effects of some working parameters like pH, dye initial concentration, temperature and contact time on the adsorption of MB by CHAC were also studied. The results of pH effect reveal that the miniimum adsorption of the dye occurred at pH = 2 and the maximum at pH = 11. The dye adsorption was found to increase with increasing initial dye concentration and the percentage removal of the dye and the amount adsorbed on the surface of the adsorbent both showed significant increase with increase in temperature up to 35oC. The effect of contact time on the percent removal of MB dye showed a decreasing trend as the dye initial concentration increased. Studies of the adsorption kinetics based on both the pseudo-second-order and the intra-particle diffusion models indicated that the diffusion of dye molecules onto the adsorbent surface could be the rate determining step for the mechanism of adsorption of MB on the CHAC