**4. Conclusions**

Different AOPs (photocatalysis, Fenton and photo-Fenton reactions) were investigated for the degradation of the IMI insecticide. Two CeO<sup>2</sup> samples were tested, one prepared with the conventional precipitation route and another one modifying the as-prepared CeO<sup>2</sup> by exposing it to solar light irradiation in a hydrogen stream. The latter treatment allowed to obtain a more defective ceria with increased performance in the solar photo-Fenton reaction. This hybrid AOP obtained the best degradation rate of the IMI. The photon interaction with the surface of CeO<sup>2</sup> led to a loss of oxygen with the formation of Ce3<sup>+</sup> centers, which is essential to boost the degradation rate of the pesticide degradation through the photo-Fenton process. The solar irradiation in a reducing atmosphere could obtain a defective ceria that can be exploited to explore new synergisms between different AOPs for wastewater purification over non-conventional photocatalysts/Fenton materials. Furthermore, the investigated materials did not exhibit critical toxicity.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/10/4/446/s1, Figure S1: Influence of the H2O<sup>2</sup> concentration.

**Author Contributions:** Conceptualization R.F. and G.I.; Catalytic tests R.F. and S.A.B.; Investigations and writing R.F.; Raman measurements L.D.; Toxicity tests M.V.B.; R.P. and E.M.S.; Review and editing G.I., S.S. and V.P. All authors have read and agreed to the current version of the manuscript.

**Funding:** This work was partially founded by the Micro WatTS project, Interreg V. A. Italia-Malta (CUP: B61G18000070009). R.F. thanks the PON project "AIM" founded by the European Social Found (ESF) CUP: E66C18001220005 for the financial support. R.P. thanks the PON project "AIM" founded by the European Social Found (ESF) CUP: E66C18001300007 for the financial support.

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