Calorimetric studies of removal of nonsteroidal anti-inflammatory drugs diclofenac and dipyrone from water

Chitosan microspheres were applied to remove the pollutants diclofenac and dipyrone from water. Adsorption studies were adjusted to Langmuir equation. The maximum number of adsorbed moles gave 5.25 × 10⁻⁴ and 4.83 × 10⁻⁴ mol of diclofenac and dipyrone, respectively, per gram of chitosan microspheres. The interactions in solid/liquid interface were calorimetrically followed and gave endothermic values: +22.1 ± 1.3 and +48.7 ± 1.5 kJ mol⁻¹, respectively, for the same sequence. Both Gibbs energy values were negative. Adsorption processes were accompanied by an increase in entropy. These interactions were studied by FTIR spectroscopy which showed a strengthening of the CN stretching (dislocated shifts from 1,325 to 1,371 cm⁻¹) related to a weakening of the NH stretch caused by the interaction with drugs.