Adsorption of Tartrazine onto Activated Carbon Based Cola Nuts Shells: Equilibrium, Kinetics, and Thermodynamics Studies

Abstract

The uptake of tartrazine from its aqueous solution by powdered activated carbon prepared from cola nut shells chemically activated with potassium hydroxide (ACK) and phosphoric acid (ACP) has been investigated using kinetics models. Batch isotherm data were analysed with the pseudo-first order, pseudo-second order model as well as the intraparticle diffusion model. For structural elucidation, the materials were characterized using FTIR, XRD and SEM. These analyses revealed that the activated carbons (ACK and ACP) were predominantly mesoporous with several oxygen-containing functional groups dispersed on their surface. The reaction was systematically investigated under various experimental conditions such as contact time, adsorbent dose and pH. For the two adsorbents, the quantity adsorbed of 19.256 mg/g and 18.196 mg/g respectively for ACP and ACK at respective contact times of 5 and 10 min were obtained. The adsorption data were tested with the Langmuir, Freundlich models. Langmuir model was found to best describe the adsorption of tartrate ions with maximum monolayer adsorption capacities of 24.57 and 21.59 mg/g for ACP and ACK, respectively. Results analysis indicated clearly that the pseudo-second order kinetic rate model best fitted the experimental data and therefore was the adsorption controlling mechanism for both adsorbents. Thermodynamic studies revealed that the adsorption process was spontaneous and exothermic for ACP with increased randomness at the solid solution interface, then exothermic but non-spontaneous for ACK. The results show that these activated carbons could be an alternative for more costly adsorbents for the purpose of tartrate ions elimination.