In-situ constructing Se/SnO2/SnS2/SnSe2/SnSe nanocomposites for rapid detection and highly-sensitive H2S gas sensor

The bare SnS2 usually exhibits many undesirable gas-sensing performances such as low selectivity, slow response/recovery, and poor stability in the application field of gas sensors. Heterojunction and morphology engineering are crucial for achieving high- performance SnS2-based gas sensors. Here, we firstly fabricated SnS2 nanoflowers, and subsequently on the SnS2 nanoflowers’ microstructure in-situ constructed Se/SnO2/SnS2/SnSe2/SnSe nanocomposites by two-step solvothermal methods. In contrast to the pure SnS2 and SnSe2 samples, the Se/SnSe2/SnS2-based composites display a remarkable improvement in the H2S sensing properties. The phase composition, microstructure, and gas-sensing properties of the composites are well modulated by varying the S/Se ratio. The test results reveal that the S/Se-0.2 (SnS2/SnSe2 ratio = 1:5) sensor exhibits a high gas response of Ra/Rg = 11.07 and a fast response and recovery of 6 s/148 s toward 200 ppm H2S at 200 °C. More importantly, the S/Se-0.2 sensor shows remarkable selectivity, good reproducibility, and excellent long-term stability to H2S with a low detection limit of 250 ppb. The sensing mechanism is also investigated based on XRD, XPS, and SEM analysis. The strengthened gas sensitivity for the S/Se-0.2 sensor is the synergistic effects of the microstructure, defects, and multiple heterojunctions. Our work paves a new road for the design and optimization of SnS2-based gas sensors.