MoO2 Pump-Enhanced Flexible TiO2 Nanojungle-Based Chemiresistors for Rapid Room-Temperature Detection of H2S at Parts-per-Billion Levels

In this study, we developed a gas sensing platform that can sensitively and specifically detect trace H₂S in a high-humidity atmosphere at RT. Upon integrating a carbon nitride (C₃N₄) nanofilm and molybdenum dioxide (MoO₂) nanosheets onto nanojungle-like TiO₂ nanotube arrays (TiNTs), the fabricated chemiresistor showed rapid response (38 s)/recovery (58 s) abilities and remarkable detection sensitivity for H₂S at concentrations down to 2 ppb, with an estimated detection limit of 1.13 ppb at RT and room-environmental light (REL). Importantly, the gas sensor exhibited satisfactory H₂S sensing performance even in dark conditions with a response of 1.9 at 200 ppb. In this design, apart from the architectural advantages of the nanojungle-like TiNTs for accelerating the gas flow efficiency and the abundant sensing sites provided by the C₃N₄ film, the MoO₂ nanosheets act as the essential electron pump not only for the H₂S response but also for the subsequent recovery process in air. After employing the MoO₂ pump onto C₃N₄/TiNTs, the response time and recovery time of the system are shortened to ∼35 and ∼11%, respectively. Moreover, we demonstrated the good performance of the flexible gas sensor in detecting trace H₂S in human exhaled breath with good humidity resistance. These results highlight the possibility of designing chemiresistors operating in RT and REL conditions and to use these environmentally friendly TiO₂-based sensors in real applications.