A modeling analysis for the assessment of ibuprofen adsorption mechanism onto activated carbons

This work is an experimental analysis of the adsorption of ibuprofen (IBP) onto a granular activated carbon. Ibuprofen is a NSAID (non-steroidal anti-inflammatory drug) and is now an emerging contaminant of the aquatic environment. The effect of IBP concentration, pH and temperature on the equilibrium adsorption capacity is investigated through batch tests. The experimental results show that the highest adsorption capacity is observed under acidic pH and high temperature conditions. The combined effect of pH and temperature on IBP dissociation in water seems to play a major role in determining the IBP adsorption capacity of the activated carbon. Low pH and high temperature, in fact, reduce the IBP dissociation grade and increase the concentration of the non-ionized IBP species, which is likely to have a higher adsorption capacity with respect to the ionized one. The study puts forward a model to describe the IBP adsorption mechanism considering the variability of the dissociation grade. The model is based on the multicomponent Langmuir adsorption theory applied to the ionic species in solution. It shows that the adsorption capacity is strictly dependent on the IBP speciation in solution, allowing for a correct interpretation of the effects pH and temperature on IBP adsorption capacity. Finally, one of the main goals of this model is to preserve the exothermicity of the adsorption phenomena despite the trend observed in the experimental results: the increase in adsorption capacity with temperature appears to be related to a lower level of IBP dissociation