Chemo-resistive NO2 sensor using La-doped WO3 nanoparticles synthesized by flame spray pyrolysis

Detection of NO 2 attracted increasing interest to check the air quality and monitor exhaust emission of combustion facilities. In this study, the flame spray pyrolysis (FSP) method was used to prepare the La-doped WO 3 nanoparticles as NO 2 sensing materials for the first time. The FSP-made La-doped WO 3 nanoparticles showed that the doped La atoms were dispersed homogeneously on WO 3 particles in the form of La 2 O 3 . It was observed that in the concentration range of 150–1200 ppb at 125 ℃ , the WO 3 sensing responses were enhanced by La doping from 2.5 at% to 10 at%, and exhibited the highest sensing response when the La doping ratio was 7.5 at%. The 7.5 at% La-doped WO 3 shows the highest response (74.2) toward 900 ppb NO 2 at 125 ℃ with response/recovery times of 23 and 35 s. Then, the high-resolution XPS spectra and sensing mechanism were combined to investigate the La-doping effects, it can be found that the enhancement of La doping might result from the enriched vacancy oxygen and more absorption sites, as well as the p-n heterojunction that drives more electrons to react with NO 2 . Moreover, the sensor using 7.5 at% La-doped WO 3 presented an excellent anti-interference performance to single NH 3 , SO 2 , CO, CO 2 , and CH 4 , but were disturbed by ppm-level NH 3 and SO 2 coexisted with NO 2 . It also exhibited good resistance to RH fluctuation and good stability.