n-n type In₂O₃@-WO₃ heterojunction nanowires: enhanced NO₂ gas sensing characteristics for environmental monitoring

Solvothermal synthesis of 1D n-In₂O₃@n-WO₃ heterojunction nanowires (HNWs) and their NO₂ gas sensing characteristics are reported. The n-In₂O₃@n-WO₃ HNWs have been well-characterised using XRD, Raman spectroscopy, XPS, SEM and HRTEM analyses. The NO₂ sensing performance of n-In₂O₃@n-WO₃ HNWs showed superior performance compared with pristine WO₃ NWs. Due to the distinctive configuration of WO₃-In₂O₃ heterojunctions, the n-In₂O₃@n-WO₃ HNWs demonstrated remarkable sensitivity reaching 182% in response towards 500 ppb of NO₂ gas at operating temperature of 200°C which is nearly 3.5 times greater than the response observed with pristine WO₃ (50%). Moreover, the n-In₂O₃@n-WO₃ HNWs also exhibited fast response (8-13 s)/recovery (54-62 s) time characteristics. A plausible sensing mechanism has been discussed. The enhancement in sensor characteristics shows that n-In₂O₃@n-WO₃ HNWs could serve as a promising material for high-performance NO₂ gas sensors for real-time environmental monitoring applications. This work could provide new understandings of the sensing mechanism of n-In₂O₃@n-WO₃-based heterojunction nanowires, which can be applied to the design of novel n-n type MOS heterojunction materials for the application of low-temperature real-time high-performance NO₂ sensors.