Mechanistic insights on rational engineering of ternary system for SO2 detection across ppb and ppm levels

Real-time monitoring of sulphur dioxide (SO 2 ) across both trace (ppb) and higher (ppm) ranges is crucial for efficient environmental, household, and industrial applications. Thus, herein binary and ternary structures derived from In 2 O 3 /MoS 2 , SnO 2 /MoS 2 , In 2 O 3 /SnO 2 /MoS 2, and SnO 2 /In 2 O 3 /MoS 2 were successfully developed to boost optical, structural, and SO 2 gas sensing capabilities. Structural analysis confirmed that the individual components integrated successfully, yielding well-defined heterostructures with strong interfacial contact between the metal oxides and the MoS 2 layers. Morphological studies showed that porous nanoplatelets and hierarchical structures, especially in the ternary composites, increased the surface area and provided numerous active sites for gas adsorption. The In 2 O 3 /SnO 2 /MoS 2 sensor demonstrated the best performance and selectivity for SO 2 over a wide concentration range, spanning both ppm and ppb levels, at 100 °C, compared with the binary counterparts and the reversed stacking configuration. These improved sensing abilities are due to synergistic effects within the heterostructure, including efficient charge transfer at the In 2 O 3 /SnO 2 interfaces, the high reactivity of MoS 2 , and the porous nanoplatelet, which enables fast gas diffusion and adsorption. Multiple heterojunctions modulated the electron-depletion layer during SO 2 interaction, thereby enhancing sensitivity and selectivity compared to binary versions. These results emphasize the role of heterointerface engineering and porous nanostructure design in creating high-performance gas sensors for detecting sulfur gases at trace levels.