Sandwich-Structured In2S3/In2O3/In2S3 Hollow Nanofibers as Sensing Materials for Ethanol Detection

Core–shell heterojunction nanostructure-based sensors often suffer from the blocking effect from the shell layer. Here, a type of sandwich-structured hollow nanofiber of In2S3/In2O3/In2S3 (ISOS HNF) was designed via an electrospinning technique combining with postvulcanization treatments. The resultant ISOS HNF possesses double In2S3/In2O3 heterointerfaces at both sides of In2O3 tube walls, which highly enhance the junction effect on the electron transport during the gas-sensing processes. Also, the two In2S3 coatings are particle-filled and porous, which often allows the target gas to easily diffuse through them to the In2O3 core. As a result, toward 100 ppm ethanol at a work temperature of 200 °C, the ISOS HNF sensors show a high response improved by 23% and 76% compared to those of the In2S3/In2O3 core–shell NF and In2O3 HNF ones, respectively. Moreover, the ISOS HNF sensors also exhibit a fast response/recovery rate (<1 s/25 s) and a good gas selectivity property. Series analysis indicates that this highly improved response is mainly due to the double In2S3/In2O3 heterointerfaces and increased O vacancies, the accelerated response/recovery rate is due to the double-constructed heterojunction and the suitable mesopores in the coatings, and the improved gas selectivity is due to the In2S3 shell.