Visible-Light Modulated Nanostructured SnS/SnS₂ Heterojunctions for Room Temperature ppb-Level NO₂ Gas Sensor

Tin disulfide (SnS 2 ) has attracted considerable interest in NO 2 detection, owing to its appropriate band structure and strong electronegativity. However, SnS 2 -based sensors have encountered challenges in practical room-temperature applications, mainly due to high baseline resistance and poor recovery performance. Herein, we propose a nanostructured SnS/SnS 2 heterojunction sensor for room-temperature NO 2 detection at the parts per billion level under visible light modulation. The nanostructured SnS/SnS 2 heterojunctions were synthesized by in situ formation of 5 nm SnS nanoparticles on SnS 2 nanosheets through vacuum heating. The composites maintained nanosheet structure with dimensions of approximately 0.5 μm. This nanostructured design significantly enhances the gas-sensing performance. The sensor demonstrates exceptional sensitivity to 0.1 ppm of NO 2 under 530 nm illumination (optical power of 50 mW/cm 2 ), achieving a response of 3.0. Moreover, the sensor exhibits exceptional selectivity and long-term stability. These improvements are likely to result from the construction of a nanostructured p–n heterojunction between SnS and SnS 2, which promotes efficient charge transport and establishes an energy barrier within the heterojunction. Additionally, the enhanced separation efficiency of photogenerated carriers within the sensing material and enhanced surface activity contribute to the elevated response value of the sensor. This work thus demonstrates that the nanostructured SnS/SnS 2 heterojunction holds great potential as a nanostructure for room temperature ppb-level NO 2 detection with visible light modulation.