| Summary: | Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO<sub>2</sub>, employed as a non-conventional photocatalyst/Fenton-like material. The first one has been prepared by chemical precipitation with KOH, while the second one has been obtained by exposing the as-synthetized CeO<sub>2</sub> to solar irradiation in H<sub>2</sub> stream. This latter treatment led to obtain a more defective CeO<sub>2</sub> (coded as “grey CeO<sub>2</sub>”) with the formation of Ce<sup>3+</sup> sites on the surface of CeO<sub>2</sub>, as determined by Raman and X-ray Photoelectron Spectroscopy (XPS) characterizations. This peculiar feature has been demonstrated as beneficial for the solar photo–Fenton reaction, with the best performance exhibited by the grey CeO<sub>2</sub>. On the contrary, the bare CeO<sub>2</sub> showed a photocatalytic activity higher with respect to the grey CeO<sub>2</sub>, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO<sub>2</sub> reported here, allows to tune and modify the physico-chemical properties of CeO<sub>2,</sub> allowing a choice of different CeO<sub>2</sub> samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity.
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