Adsorptive removal of a synthetic textile dye using cocoa pod husks

Abstract

The adsorption of a synthetic textile dye (Remazol Brilliant Black Reactive) on cocoa pod husk-based activated carbon was investigated in batch process. The adsorbent prepared was characterized by gas adsorption surface analysis (Brunauer Emmett Teller, BET), scanning electron microscopy, and Fourier transform infrared spectroscopy. The effects of initial dye concentration, contact time, solution temperature, and solution pH were evaluated. Equilibrium data were fitted to Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, the first being the best with maximum monolayer coverage of 111 mg g⁻¹. Kinetic data were fitted into pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models; the pseudo second-order model provided the best correlation. Maximum adsorption was observed at pH 7. Standard free energy, standard enthalpy, and standard entropy were also calculated. The adsorption interaction was found to be endothermic and spontaneous. Both the mean free energy of adsorption and the activation energy show that the mechanism is by physisorption.

Keywords:

• adsorption
• cocoa pod husk activated carbon
• Remazol Brilliant Black Reactive dye
• isotherm
• kinetics

Acknowledgments

The authors gratefully acknowledge the financial support received in the form of research grants (PJ/KIMIA 6035296, PJ/KIMIA 814003, and PJ/AWAM 814021) from Universiti Sains Malaysia that resulted in this article. The 1-year Post Doctoral Fellowship jointly awarded by USM-TWAS to Dr O.S. Bello (FR Number: 3240223483 in Year 2009) of the Department of P/A Chemistry, Ladoke Akintola University of Technology, P.M.B 4000, Ogbomoso, Oyo State. Nigeria and the 1-year study leave granted him by his home institution to honor this fellowship are both acknowledged.