Equilibrium and kinetics studies of fluoride ions adsorption on CeO2/Al2O3 composites pretreated with non-thermal plasma

The removal of fluoride from aqueous solution using the original and non-thermal plasma (NTP) modified CeO2/Al2O3 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 ΔGθ, ΔSθ, ΔHθ and Ea 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 ΔSθ increased from 78.42 J/mol K to 93.42 J/mol K, the Ea decreased from 57.52 kJ/mol to 54.60 kJ/mol and the ΔGθ (363 K) decreased from −6.82 kJ/mol to −8.06 kJ/mol. The negative value of ΔGθ indicates that the adsorption occurs via a spontaneous process, the decrease in the value of Ea indicates that the adsorption of fluoride on NTP modified adsorbents is more favourable.