Hybrid Noble-Metals/Metal-Oxide Bifunctional Nano-Heterostructure Displaying Outperforming Gas-Sensing and Photochromic Performances

As nanomaterials are dominating 21st century’s scene, multiple functionality in a single (nano)­structure is becoming very appealing. Inspired by the Land of the Rising Sun, we designed a bifunctional (gas-sensor/photochromic) nanomaterial, made with TiO₂ whose surface was simultaneously decorated with copper and silver (the Cu/Ag molar ratio being 3:1). This nanomaterial outperformed previous state-of-the-art TiO₂-based sensors for the detection of acetone, as well as the Cu–TiO₂-based photochromic material. It indeed possessed splendid sensitivity toward acetone (detection limit of 100 ppb, 5 times lower than previous state-of-the-art TiO₂-based acetone sensors), as well as reduced response/recovery times at very low working temperature, 150 °C, for acetone sensing. Still, the same material showed itself to be able to (reversibly) change in color when stimulated by both UV-A and, most remarkably, visible light. Indeed, the visible-light photochromic performance was almost 3 times faster compared to the standard Cu–TiO₂ photochromic materialthat is, 4.0 min versus 10.8 min, respectively. It was eventually proposed that the photochromic behavior was triggered by different mechanisms, depending on the light source used.