Activated carbons from coffee husk: Preparation, characterization, and reactive red 195 adsorption

Abstract

Activated carbons are prepared from coffee husks by chemical activation with ZnCl2 and are characterized by employing Brunauer, Emmett and Teller, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Boehm titrations. The effects of ZnCl2/coffee husks, activation temperature, and activation time are studied, and the results show that the sample ACZ3-600-2 has a high surface area of 1383 m2 g−1, a high pore volume of 1.6482 cm3 g−1, and numerous surface functional groups. The adsorption of reactive red 195 onto the prepared coffee husk activated carbon can be well-described by the pseudo-second-order kinetic model and is found to be controlled by film diffusion followed by intra-particle diffusion. The adsorption isotherm data obtained at 10–40 °C are analyzed and found to follow the Sips model at lower temperatures (10 and 20 °C) and the Redlich–Peterson model at higher temperatures (30 and 40 °C). The obtained thermodynamic parameters (ΔG° < 0, ΔH° = 33.487 kJ mol−1, and ΔS° = 202.30 J K−1 mol−1) suggest that the adsorption of reactive red 195 onto the prepared activated carbon is spontaneous, endothermic, and demonstrates an increasing of randomness at the adsorbate–adsorbent interface. The investigated results show that coffee husk activated carbon is an efficient adsorbent for the removal of reactive red 195 from aqueous solutions.