Kinetics, Mechanistic, Equilibrium, and Thermodynamic Studies on the Adsorption of Acid Red Dye from Wastewater by γ-Fe2O3 Nanoadsorbents

The presence of dyestuffs in wastewater poses an environmental concern since these organic contaminants are toxic to aquatic and non-aquatic life. In addition, these contaminants are difficult to remove or biodegrade, which poses a challenge to the conventional wastewater treatment techniques. In this work, the adsorption of acid red dye 27 (AR27) onto γ-Fe2O3 nanoadsorbents was studied for the removal of red dye from aqueous solutions by the batch-adsorption technique. The experiments were carried out at different conditions of contact time, initial AR27 concentration, temperature, co-existing ions, and solution pH. It was found that the adsorption was a rapid process, and equilibrium was achieved in less than 4 minutes. The removal of AR27 decreased with the increase in solution pH and temperature. Furthermore, the addition of chloride and nitrate anions has no remarkable influence on AR27 removal efficiency. On the other hand, the effects of sulfate and bicarbonate anions on the removal of AR27 were significant. The adsorption equilibrium data fitted very well using Langmuir and Freundlich adsorption isotherm models. The data obtained from adsorption isotherms at different temperatures were used to calculate thermodynamic quantities of adsorption, such as standard Gibbs free energy change [image omitted], enthalpy change [image omitted], and entropy change [image omitted]. The adsorption process was found to be spontaneous, exothermic and physical in nature. The results indicate that γ-Fe2O3 nanoadsorbents could be employed for the removal of dyes from wastewater.