Comparative study on the gas-sensing performance of ZnO/SnO2 external and ZnO–SnO2 internal heterojunctions for ppb H2S and NO2 gases detection

The design of hetero-nanojunctions can greatly amplify the gas-sensing performance of conventional metal oxide gas sensors. In this study, the composite nanofibers (NFs) of ZnO–SnO2 internal heterojunctions (HJs) and the mixed NFs of ZnO/SnO2 external HJs were realized by using the electrospinning technique. Then, the gas-sensing characteristics of the as-synthesized NFs toward H2S and NO2 gases were systematically investigated and compared. The effects of the internal and external nanojunctions of the hetero-NF-based gas sensors were also explored. Results showed that the ZnO–SnO2 composite NFs demonstrate a higher response than those of the ZnO/SnO2 mixed NFs, as well as bare ZnO and SnO2 NFs. Also, the cross responses of the hetero-NF sensors toward 200 ppm CO, 250 ppm H2, and 250 ppm NH3 were examined. The gas-sensing mechanism of the internal and external HJs of composite ZnO/SnO2 and mixed ZnO/SnO2 NFs was analyzed. The remarkable enhanced gas-sensing performance of hetero-NFs was mainly attributed to the formation of internal HJs.