Light-Assisted and Humidity-Tolerant ppb-Level NO ₂ Detection at Low Temperature Using a Ternary In ₂ O ₃ @ZnO@PPy Hybrid

The pervasive issue of nitrogen dioxide (NO₂) as a hazardous air pollutant requires the development of high-performance gas sensors with high sensitivity, long-term stability, and low-temperature operation. While metal oxide semiconductors (MOS), such as In₂O₃ and ZnO, have been extensively investigated for this purpose, their practical application is often limited by the requirement for high operating temperatures and insufficient sensitivity to parts-per-billion (ppb) concentrations. Herein, we report a hierarchical ternary hybrid material, In₂O₃@ZnO@PPy, specifically designed for near-room temperature and light-assisted NO₂ detection. The collective synergistic effects arising from the hierarchical architecture, inter-semiconductor heterojunctions, and conductive polymer integration enable the In₂O₃@ZnO@PPy sensor to exhibit exceptional sensitivity to NO₂ at a low operating temperature of only 70 °C under blue-light excitation. The response value to 10 ppm NO₂ is as high as 221.4. The optimized sensor demonstrates an ultralow limit of detection of 50 ppb. More importantly, the hybrid exhibits remarkable humidity tolerance, maintaining high sensing performance even at 80% relative humidity. Surface wettability analysis suggests that PPy incorporation modulates the interfacial interaction with water molecules, which helps alleviate humidity-induced interference during NO₂ detection. The device further exhibits excellent repeatability, long-term stability, and strong selectivity against common interferents. These findings establish a light-assisted strategy for ppb-level gas sensing and provide a generalizable route for designing multifunctional hybrid materials for environmental monitoring and health diagnostics.