• A novel PbS QDs–PbMoO4–MoS2 ternary nanocomposite sensor achieves a response of 44.5% to 1 ppm NO2 at room temperature, ~5 times higher than pure MoS2.
• The sensor exhibits exceptional selectivity toward NO2 with negligible cross-response to interfering gases, addressing a key limitation of traditional metal-oxide sensors.
• DFT calculations reveal that the enhanced sensing performance arises from the synergistic receptor function of PbS QDs and PbMoO4 nanoparticles and the transducer function of MoS2 nanosheets.
• The room-temperature operation, full recovery, and short response/recovery times make this sensor promising for energy-efficient, portable, and safe NO2 monitoring applications.