**CeO<sup>2</sup> for Water Remediation: Comparison of Various Advanced Oxidation Processes**

**Roberto Fiorenza <sup>1</sup> , Stefano Andrea Balsamo <sup>1</sup> , Luisa D'Urso <sup>1</sup> , Salvatore Sciré 1 , Maria Violetta Brundo <sup>2</sup> , Roberta Pecoraro <sup>2</sup> , Elena Maria Scalisi <sup>2</sup> , Vittorio Privitera <sup>3</sup> and Giuliana Impellizzeri 3,\***


Received: 30 March 2020; Accepted: 20 April 2020; Published: 21 April 2020

**Abstract:** 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 CeO2, 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<sup>2</sup> to solar irradiation in H<sup>2</sup> stream. This latter treatment led to obtain a more defective CeO<sup>2</sup> (coded as "grey CeO2") with the formation of Ce3<sup>+</sup> sites on the surface of CeO2, 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 CeO2. On the contrary, the bare CeO<sup>2</sup> showed a photocatalytic activity higher with respect to the grey CeO2, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO<sup>2</sup> reported here, allows to tune and modify the physico-chemical properties of CeO2, allowing a choice of different CeO<sup>2</sup> samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity.

**Keywords:** ceria; pesticide; photocatalysis; photo-Fenton; AOPs
