Adsorption of phenol and methylene blue from aqueous solutions by pyrolytic tire char: Equilibrium and kinetic studies

Abstract

Acid-treated pyrolytic tire char (PTC) was studied as an adsorbent for the removal of phenol and methylene blue (MB) dye from aqueous solutions. PTC was derived via pyrolysis of used rubber tires at 450°C in oxygen-free atmosphere. Textural characteristics and surface chemical nature of the adsorbent were examined through a battery of techniques such as X-ray diffraction, porosimetry, Boehm titration, and point of zero charge determination. The adsorption characteristics of phenol and MB dye were evaluated on the basis of equilibrium and kinetic studies. The adsorption kinetic data fitted better to pseudo-second kinetic model. Equilibrium isotherms were analyzed by Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Frumkin models. Langmuir and Freundlich isotherm models were found to fit the adsorption data of phenol and MB, respectively. The maximum adsorption capacities of phenol and MB on PTC were found to be 51.92 and 65.81mgg−1, respectively. In the case of phenol, the adsorption mechanisms can be attributed to π–π electron donor/acceptor interaction, hydrogen bonding of phenol with surface groups of PTC. On the other hand, electrostatic attraction between the carboxylic groups of PTC surface and cationic dye is responsible for the adsorption of MB. The effect of temperature on the organics’ adsorption was studied and the thermodynamic parameters (ΔH, ΔS and ΔG) were determined for each of the studied systems. The adsorption for both pollutants was found to be thermodynamically spontaneous (ΔG<0), although it was exothermic (ΔH<0) for phenol vs endothermic (ΔH>0) for MB.