Bifunctional gas sensor based on Bi2S3/SnS2 heterostructures with improved selectivity through visible light modulation

The effective monitoring of hazardous gases at room temperature is extremely indispensable in the "Internet of things" application; however, developing bifunctional gas sensors for advanced sensing platforms still remains a challenge. Herein, we demonstrate a visible-light-modulated strategy to realize the bifunctional detection of NO2 and H2S by using Bi2S3/SnS2 heterostructures as sensing materials. The sensor based on Bi2S3/SnS2 exhibited superior sensitivity toward NO2 under light irradiation and high selectivity to H2S in the dark at room temperature; additionally, it achieved ultrahigh responses (14.0 (R-g/R-a) towards 500 ppb NO2 and 12.3 (R-a/R-g) towards 500 ppb H2S). Such distinctive light-dependent sensing behavior is mainly attributed to the different gas-sensing mechanisms of Bi2S3/SnS2 toward NO2 (physisorption model) and H2S (oxygen absorbate-mediated model). As confirmed by in situ XPS characterization, the decrease in surface-adsorbed oxygen on Bi2S3/SnS2 under light illumination offers the opportunity to modulate the number of active adsorption sites and consequently obtain bifunctional gas-sensing characteristics. In addition, the heterojunction effect, which is beneficial for interfacial charge transfer, also contributes to the improved sensing performance. Moreover, the Bi2S3/SnS2 sensor presented rapid response-recovery speed, outstanding repeatability, and reliable stability to ppb-level target gases. This work offers an alternative strategy to designing bifunctional gas sensors through light modulation, which might significantly encourage the development of other smart sensing materials and further expand their potential applications.