**4. Conclusions**

Due to concerns related to water decontamination from pollutants, this paper reported the use of chitosan films for the removal of Kp from water, with regard to more ustainable and greener industrial applications. The bio-sorption process is very interesting, since about 90% of the Kp was removed in 2 h at most. The sorption process was investigated at several temperature values, indicating that, upon increasing the temperature, the removal of Kp from water increased. The thermodynamic parameters were calculated, observing that the process was spontaneous (ΔG◦ < 0) and endothermic (ΔH◦ < 0), and that it occurred with an increase in entropy. From a kinetic point of view, the pseudo second-order kinetic model agreed well with the experimental data, indicating that the bio-sorption was dependent on the amounts of Kp and adsorbent. In fact, upon increasing the amount of CH and the concentration of the Kp solution, the pollutant removal efficiencies affected the adsorption capacities. The high affinity between the NSAID and CH was ascribed to the presence of electrostatic interactions. Indeed, the adsorption was largely affected by the pH value of the Kp solution and by the presence of salts.

Considering that the pKa of Kp is about 4, the maximum removal was observed at pH 5, while, upon further increasing the pH values of the Kp solution, the NSAID removal decreased. In accordance with the measured pHZPC of the CH (~7), below this pH value, the interaction between Kp<sup>−</sup> and CH was observed. However, below the pKa of the Kp, the main form Kp-H reduced the affinity toward the adsorbent. The same finding was observed at basic pH values, conditions in which the adsorbent was negatively charged and repulsions between Kp− and the adsorbent occurred. An interaction between the Kp carboxylic moiety and the chitosan amino groups was, thus, proposed and confirmed by experiments of adsorption performed in the presence of salts, which inhibited the Kp removal. Interestingly, the use of 0.25 M NaCl was found to be suitable for the desorption of the adsorbed Kp, enabling the reuse of the pollutant and the recycling of the adsorbent for several cycles, extending the CH lifetime. The reuse of the recovered pollutants and the use of CH, proposed in this work, exhibit great benefits for the environment through the reuse of products for cleaner production technologies.

**Author Contributions:** Conceptualization, V.R.; methodology, J.G., R.R., and P.F.; software, V.R. and S.N.; validation, V.R. and P.C.; formal analysis, J.G. and V.R.; investigation, V.R. and P.F.; resources, P.C.; data curation, V.R. and P.C.; writing—original draft preparation, V.R.; visualization, V.R. and P.F.; supervision, P.C.; project administration, P.C. and P.F.; funding acquisition, P.C. and P.F.

**Funding:** This research was funded by the LIFE+ European Project named LIFE CLEAN UP ("Validation of adsorbent materials and advanced oxidation techniques to remove emerging pollutants in treated wastewater"—LIFE 16 ENV/ES/000169).

**Acknowledgments:** We gratefully acknowledge Sergio Nuzzo for skillful and technical assistance.

**Conflicts of Interest:** The authors declare no conflicts of interest.
