Increased Active Sites and Charge Transfer in the SnS2/TiO2 Heterostructure for Visible-Light-Assisted NO2 Sensing.

Tin disulfide (SnS2) has been extensively researched as a promising sensing material due to its large electronegativity, suitable band gap, earth abundance, and nontoxicity. However, the poor conductivity and slow response/recovery speed at room temperature greatly hinder its application in high-performance practical gas sensors. Herein, to promote the study of SnS2-based gas sensors, a hierarchical SnS2/TiO2 heterostructure was synthesized and used as a sensing material to detect NO2 with the help of light illumination. Through the synergistic effect of the SnS2/TiO2 heterostructure and 525 nm light activation, the NO2 sensor based on the SnS2/TiO2 heterostructure exhibited a high response factor of 526% toward 1 ppm NO2 and a short response/recovery time of 43/102 s at room temperature due to the enhanced charge transfer and increased adsorption sites, which was superior to the vast majority of other NO2 sensors. An obvious decrease in the surface-adsorbed oxygen content based on the X-ray photoelectron spectroscopy measurement further confirmed that light illumination was helpful to clear the surface of SnS2/TiO2 and thus increased active sites for NO2 sensing. In addition, a flexible SnS2/TiO2 sensor was also fabricated to confirm its potential application in portable and wearable devices.