In2O3–ZnO nanotubes for the sensitive and selective detection of ppb-level NO2 under UV irradiation at room temperature

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In2O3–ZnO nanotubes were prepared by a solvent thermal method using electrospun indium nitrate–polyvinyl pyrrolidone [In(NO3)3–PVP] nanofibers as a sacrificial template. The sensing properties toward NO2 of this kind of new emerging sensing material were explored. Compared with as-electrospun In2O3 nanofibers, the In2O3–ZnO composite nanotubes exhibited higher responses and better selectivity to NO2. The response of the In2O3–ZnO nanotubes to 500 ppb NO2 at room temperature (RT, 25 °C) under UV irradiation was as high as to 32.73, which was 3.33 times higher than that of the In2O3 nanofibers. Moreover, even under a high relative humidity of 80%, the RT NO2 response of the In2O3–ZnO composite nanotubes can still reach up to 3.50–500 ppb. The enhanced NO2 sensing characteristics were mainly ascribed to the formation of In2O3–ZnO n–n heterojunctions, the enhanced light absorption, and the increased oxygen vacancy proportion. The results suggested that In2O3–ZnO nanotubes had good potential for the selective and sensitive detection of ppb-level NO2 at RT.