Study of Rhodamine B adsorption onto activated carbon from spent coffee grounds

Abstract

Activated carbon has been widely used as an adsorbent for heavy metals and organic compounds. Bamboo, coconut shell, oil palm shell, and residual agricultural materials are often used as organic material to be used for activated carbon. The purpose of this study is to make activated carbon from spent coffee grounds (SCG) used as an adsorbent for Rhodamine B removal. In this work, activated carbon was prepared from SGC via physical and chemical activation. The SCG was carbonized at 500 °C for 45 minutes with poor oxygen. The chemical activation process was performed by soaking the carbonized SCG in a solution of 2 M H3PO4 for 24 h. Identification of surface morphology of spent coffee grounds activated carbon (SCGAC) was conducted by scanning electron microscopy (SEM). The pH of the solution, the contact time, and the initial concentration of Rhodamine B which are parameters that affect the adsorption have been optimized. The pseudo-second-order kinetics model, intraparticle diffusion, and the Elovich model were chosen to evaluate the kinetic adsorption of Rhodamine B onto the surface of SCGAC by analyzing data of the effect of contact time on the amount of Rhodamine B adsorbed on SCGAC. Equilibrium data obtained from variations in the concentration of Rhodamin B against the amount of Rhodamine B adsorbed were analyzed using isotherm adsorption models of the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich. The optimum conditions of Rhodamine B adsorption onto SCGAC was at pH 2.5 and contact time 90 min. The kinetic model of pseudo-second-order is the most fit to illustrate the adsorption of Rhodamine B onto SCGAC in the both physical and chemical activations. The equilibrium data of adsorption could be the best fit by the Langmuir isotherm model, in which the capacity of maximum adsorption of Rhodamine B on SCGAC with physical and chemical activation was 2.5961 mg.g−1 and 4.0717 mg.g−1, respectively.