Enhanced spatial charge separation and gas adsorption in Bi2WO6 facet junction for efficient visible light-excited gas detection at room temperature

Enhancing the room temperature gas sensing capabilities of semiconductor sensors through light excitation has emerged as a prominent research focus in recent years. However, challenges such as the high photo-generated charges recombination rate and poor visible light absorption of representative semiconductor gas sensing materials have posed significant issues. To address these challenges, Aurivillius type Bi2WO6 with exceptional visible light absorption was chosen as the model material to explore facet junctions in semiconductor gas sensors for the first time. The experiment successfully achieved the self-construction of facet junctions in Bi2WO6 single crystal microplates, exposing both {001} and {010} facets. It was observed that the facet junction, with an optimal facets proportion, not only controlled gas adsorption but also facilitated the efficient separation of photo-generated charges across the anisotropic facets through surface band bending and internal fields, thus enabling the efficient detection of acetic acid under visible light LED excitation at room temperature. Through first-principle calculations, in-situ infrared spectroscopy and other spectroscopic techniques, the gas sensing mechanism was systematically elucidated. This study offers new insights into enhancing the gas sensing performance of light-excited semiconductor gas sensors through facet junction design. Moreover, it significantly enriches our understanding of the microscopic-scale gas sensing mechanisms.