The negative values of ΔG°
showed a spontaneous nature of adsorption. The low values of ΔG° obtained
indicate that for the adsorption system studied, the sorption
mechanism may involve a chemical and a physical process. The process
favorability at higher temperatures was indicated by ΔG° increasing
with the rise in temperature, whereas the positive values of ΔH° indicate
that the adsorption of HA on oxidized activated carbons is an endothermic
process.