Mesoporous Bi₂S₃/Bi₂O₃ Heterostructure-Based Sensors for Sub-ppm NO₂ Detection at Room Temperature

Novel Bi₂S₃/Bi₂O₃ hybrid materials with unique mesoporous structures were successfully synthesized via a facile in situ elevated-temperature thermal oxidation method using the Bi₂S₃ as a precursor in air. The as-prepared Bi₂S₃/Bi₂O₃ heterostructure-based sensor exhibits an excellent performance for detecting sub-ppm concentrations of NO₂ at room temperature (RT). In the presence of 8 ppm NO₂, the sensor registers a response of approximately 7.85, reflecting a 3.5-fold increase compared to the pristine Bi₂S₃-based sensor. The response time is 71 s, while the recovery time is 238 s, which are reduced by 32.4% and 24.2%, respectively, compared to the pristine Bi₂S₃-based sensor. The Bi₂S₃/Bi₂O₃ heterostructure-based sensor achieves an impressively low detection limit of 0.1 ppm for NO₂, and the sensor has been demonstrated to possess superior signal repeatability, gas selectivity, and long-term stability. The optimal preparation conditions of the hybrid materials were explored, and the formation of mesoporous structure was analyzed. The obviously improved gas sensitivity of the Bi₂S₃/Bi₂O₃ heterostructure-based sensor can be assigned to the combined influence of electronic sensitization and its distinctive morphological structure. The potential gas-sensitive mechanisms were revealed by employing density functional theory (DFT). It was found that the formation of heterostructures could enhance the adsorption energies and increase the amount of electron transfer between NO₂ molecules and the hybrid materials. Furthermore, the electron redistribution driven by orbital hybridization between O and Bi atoms improves the capacity of NO₂ molecules to capture additional electrons from the Bi₂S₃/Bi₂O₃ heterostructures. The content of this work supplies an innovative design strategy for constructing NO₂ sensor with high performance and low energy consumption at RT.