Equilibrium and kinetics studies of fluoride ions adsorption on CeO 2/Al 2O 3 composites pretreated with non-thermal plasma

Abstract

The removal of fluoride from aqueous solution using the original and non-thermal plasma (NTP) modified CeO 2/Al 2O 3 composites was systematically studied. The adsorption was investigated in batch adsorption system, including both equilibrium and kinetics. Equilibrium adsorption data were analyzed using Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. In order to understand the mechanism of adsorption, thermodynamic parameters such as Δ G θ , Δ S θ , Δ H θ and E a were calculated. Results showed that the adsorption data were found to be well described by Langmuir model. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied to test the kinetic data, and the results revealed that the pseudo-second-order kinetic reaction as the “surface reaction” was dominated and controlled adsorption stage. The thermodynamic parameters were changed using NTP modified adsorbents. For the Δ S θ increased from 78.42 J/mol K to 93.42 J/mol K, the E a decreased from 57.52 kJ/mol to 54.60 kJ/mol and the Δ G θ (363 K) decreased from −6.82 kJ/mol to −8.06 kJ/mol. The negative value of Δ G θ indicates that the adsorption occurs via a spontaneous process, the decrease in the value of E a indicates that the adsorption of fluoride on NTP modified adsorbents is more favourable.