*Article* **Photochromic Textiles Based upon Aqueous Blends of Oxygen-Deficient WO3-x and TiO<sup>2</sup> Nanocrystals**

**Roberto Giannuzzi 1,2, Vitantonio Primiceri 1,2, Riccardo Scarfiello 1,\* , Marco Pugliese <sup>1</sup> , Fabrizio Mariano <sup>1</sup> , Antonio Maggiore <sup>1</sup> , Carmela Tania Prontera 1,3,\*, Sonia Carallo <sup>1</sup> , Cristian De Vito <sup>1</sup> , Luigi Carbone <sup>1</sup> and Vincenzo Maiorano <sup>1</sup>**

	- <sup>2</sup> Department of Mathematics and Physics "Ennio De Giorgi", University of Salento, 73100 Lecce, Italy

**Abstract:** With the main objective being to develop photochromic smart textiles, in this paper, we studied the photochromic behavior of WO3-x nanocrystals (NCs) cooperatively interacting with variable amounts of TiO<sup>2</sup> NCs. We tested several blends of WO3-x:TiO<sup>2</sup> NCs, admixed in different compositions (relative molar ratio of 4:0, 3:1, 2:2, 1:3, 0:4) and electrostatically interfacing because of opposite values of Z-potential, for photo-induced chromogenic textiles. We further monitored the photochromic sensitivity of NC-impregnated textiles after exposure to a few solvents (i.e., methanol, ethanol, and isopropanol) or when over-coated with different polymeric matrices such as natural cellulose or ionic conductive Nafion. The optimization of the compositions of the WO3-x:TiO<sup>2</sup> blends embedded in polymeric matrices, allowed the nanostructured photochromic textiles to show rapid and tunable coloration (<5 min) and bleaching kinetics (~5 in at 75 ◦C or 6 h at room temperature) along with good recovery and cycling stability. This study features a simple strategy for the widespread application of WO3-x:TiO<sup>2</sup> -based photochromic smart textiles.

**Keywords:** smart textile; photochromism; inorganic nanoparticles
