Performance of activated carbons prepared from spent tyres in the adsorption of rhodamine B in aqueous solutions.

Abstract

Activated carbons were produced from spent tyre pyrolysis char by steam or CO2 activation and evaluated for their performance in rhodamine B (RhB) adsorption in aqueous solutions. The effect of RhB starting concentration (80-150 mg L-1), contact time (0-80 min), temperature (298-318 K) and initial pH on the adsorption process was examined. Pseudo-first-order and pseudo-second-order models were carried out to fit the experimental data to derive RhB adsorption kinetics. Langmuir, Freundlich and Temkin isotherm models were applied to depict RhB adsorption behaviour of the prepared activated carbons. Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were calculated. It has been found that the activated carbons can effectively adsorb RhB due to high mesoporosity and RhB equilibrium adsorption capacity (qe) increased almost linearly with increasing total mesopore volumes, regardless of the activation agents. When BET surface areas are similar, CO2-activated carbon obtained higher qe than steam due to higher mesoporosity of CO2-activated carbon. The results show that pseudo-second-order well fitted the experimental data. RhB starting concentration increased from 80 to 150 mg L-1 causing qe increased from 158 to 251 mg g-1 but RhB removal decreased from 99.7 to 84.5%. The RhB adsorption process follows the Langmuir model and thermodynamic calculation, indicating RhB adsorption is an endothermic, spontaneous process, dominated by both chemisorption and physisorption.