Kinetics and thermodynamics of enhanced adsorption of E120 dye using activated carbon

Abstract

Purpose: To study the adsorption of dye (E120) from aqueous solution onto activated carbon. Method: Factors influencing adsorption were examined and optimized. Three adsorption isotherm models (Langmuir, Freundlich and Temkin) were investigated. Agitation time was set at 72 hours, E120 dye concentration at 10 – 80 mg/L, pH at 7, temperature at 25°C and mass at 125 mg. Results: Adsorption of E120 dye onto activated carbon was enhanced by decreasing the mass of activated carbon, pH and ionic strength of the solution and by increasing the temperature. Under optimal conditions, the maximum adsorption capacity of activated carbon for E120 dye was 10.1 mg/g at 30°C. The model parameters were 0.307 L/mg (KL), 10.1 mg/g (qm), 0.9491 (R2) for the Langmuir isotherm; 2.98 (n), 0.445 mg/g (Kf), and 0.6592 (R2) for Freundlich isotherm; and 4.59 mg/L (A), 2.23 J/mol (B), and 0.5914 (R2) for Temkin isotherm. Thermodynamic studies indicate that the adsorption of E120 dye onto activated carbon is an endothermic process with an adsorption enthalpy (ΔH) of 8.7 KJ/mol. The positive values for ΔG indicate that adsorption was non-spontaneous. The kinetic study of E120 dye adsorption showed that the adsorption process obeyed pseudo-second order kinetics. Conclusion: Commercially available activated carbon, in terms of its physical and chemical characteristics, is a superior adsorbent to other adsorbents mentioned in the literature for removal of toxic dye E120 from aqueous solutions at a high removal capacity.