Tunable Chemical Reactivity and Selectivity of WO₃/TiO₂ Heterojunction for Gas Sensing Applications

Nowadays, there is a dramatically growing demand for nanocomposite materials with new functionalities for their application in chemical gas sensors and other catalytic devices. Moreover, green synthesis methods are intensively employed in the preparation of semiconductor nanostructures to reduce the hazardous effects on human health and the environment. Here the fabrication of a nanocomposite material based on WO₃ and TiO₂ (WO₃/TiO₂) with unusual electronic band alignment and novel gas sensing properties is reported. The material is synthesized by an eco-friendly process based on the water vapor-induced oxidation of tungsten/titanium metallic films. The pristine WO₃ is highly sensitive to acetone, where the response of the material is enhanced by its operating temperature. Instead, WO₃/TiO₂ composite shows principally different sensing performance and it has a good selective response to carbon monoxide at a relatively low operating temperature. The obtained results indicate that the significant differences between the functionalities of pristine WO₃ and WO₃/TiO₂ material can be attributed to the band alignment and the direction of charge transfer in the WO₃/TiO₂ heterojunction. Hence, an efficient way for the development of WO₃/TiO₂ nanocomposites, which can be useful for the engineering and optimization of gas sensing and catalytic properties of WO₃, is presented.