*Article* **Band-Gap Engineering of Layered Perovskites by Cu Spacer Insertion as Photocatalysts for Depollution Reaction**

**Monica Raciulete <sup>1</sup> , Crina Anastasescu <sup>1</sup> , Florica Papa 1,\* , Irina Atkinson <sup>1</sup> , Corina Bradu 2,3 , Catalin Negrila <sup>4</sup> , Diana-Ioana Eftemie <sup>1</sup> , Daniela C. Culita <sup>1</sup> , Akane Miyazaki <sup>5</sup> , Veronica Bratan <sup>1</sup> , Jeanina Pandele-Cusu <sup>1</sup> , Cornel Munteanu <sup>1</sup> , Gianina Dobrescu <sup>1</sup> , Alexandra Sandulescu <sup>1</sup> and Ioan Balint 1,\***


**Abstract:** A multi-step ion-exchange methodology was developed for the fabrication of Cu(LaTa2O<sup>7</sup> )2 lamellar architectures capable of wastewater depollution. The (001) diffraction line of RbLaTa2O<sup>7</sup> depended on the guest species hosted by the starting material. SEM and TEM images confirmed the well-preserved lamellar structure for all intercalated layered perovskites. The UV–Vis, XPS, and photocurrent spectroscopies proved that Cu intercalation induces a red-shift band gap compared to the perovskite host. Moreover, the UV–Vis spectroscopy elucidated the copper ions environment in the Cu-modified layered perovskites. H<sup>2</sup> -TPR results confirmed that Cu species located on the surface are reduced at a lower temperature while those from the interlayer occur at higher temperature ranges. The photocatalytic degradation of phenol under simulated solar irradiation was used as a model reaction to assess the performances of the studied catalysts. Increased photocatalytic activity was observed for Cu-modified layered perovskites compared to RbLaTa2O<sup>7</sup> pristine. This behavior resulted from the efficient separation of photogenerated charge carriers and light absorption induced by copper spacer insertion.

**Keywords:** copper spacer; layered perovskite; phenol; photocatalysis; simulated solar irradiation
