Comparative Adsorption of Acid Blue 25 and Reactive Orange 16 onto Coconut Shell Activated Carbon: Kinetics, Isotherm and Thermodynamic Studies

Abstract

In this study, coconut shell activated carbon was used as the adsorbent. Through kinetic, isothermal model and adsorption thermodynamics methods, the adsorption process of acid blue 25 and active orange 16 by coconut shell activated carbon was deeply investigated. The results showed that this adsorbent had good adsorption performance for acid blue 25 and active orange 16. The internal pores of the adsorbent were abundant, and the equilibrium adsorption amount of the two dyes increased with the increase of the initial concentration of the dyes and the adsorption temperature. The pseudo-second-order rate equation could best describe the adsorption of the adsorbent for the two dyes. The activation energy of the adsorption of the adsorbent for the two dyes was small, mainly being physical adsorption. Under the conditions of T = 30℃ and pH = 7, the isothermal adsorption law of acid blue 25 and active orange 16 on coconut shell activated carbon conformed to the Langmuir model equation. The maximum saturated adsorption amounts were 258.48 and 248.05 mg/g, respectively, and the adsorption free energy was -8.875 and -4.436 kJ/mol, respectively. The enthalpy changes ΔH of acid blue 25 and active orange 16 were 8.688 and 7.894 KJ/mol, respectively, indicating that the adsorption was an endothermic process and irreversible. The isothermal adsorption study, adsorption kinetics and thermodynamics study all showed that under the same conditions, the adsorption effect of the two dyes on coconut shell activated carbon was: acid blue 25 > active orange 16.