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

Solvothermal synthesis of 1D n -In 2 O 3 @ n -WO 3 heterojunction nanowires (HNWs) and their NO 2 gas sensing characteristics are reported. The n -In 2 O 3 @ n -WO 3 HNWs have been well-characterised using XRD, Raman spectroscopy, XPS, SEM and HRTEM analyses. The NO 2 sensing performance of n -In 2 O 3 @ n -WO 3 HNWs showed superior performance compared with pristine WO 3 NWs. Due to the distinctive configuration of WO 3 -In 2 O 3 heterojunctions, the n -In 2 O 3 @ n -WO 3 HNWs demonstrated remarkable sensitivity reaching 182% in response towards 500 ppb of NO 2 gas at operating temperature of 200°C which is nearly 3.5 times greater than the response observed with pristine WO 3 (50%). Moreover, the n -In 2 O 3 @ n -WO 3 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 -In 2 O 3 @ n -WO 3 HNWs could serve as a promising material for high-performance NO 2 gas sensors for real-time environmental monitoring applications. This work could provide new understandings of the sensing mechanism of n -In 2 O 3 @ n -WO 3 –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 NO 2 sensors. Graphical Abstract