Flame-Spray-Synthesized La2O3-Loaded WO3 Nanoparticle Films for NO2 Sensing

In this investigation, flame-made La2O3-loaded WO3 nanoparticle films prepared with varying La contents (0–2 wt %) and spin-coating cycle numbers (1–6) were comprehensively explored for nitrogen dioxide (NO2) detection. Detailed material analysis revealed the creation of secondary La2O3 nanoparticles on primary monoclinic WO3 nanoparticles. Gas-sensing measurements were conducted toward 50–5000 ppb NO2 at 100–350 °C in dry and humid air (0–80 %RH). The obtained data dictated that the La content of 0.2 wt % and three spin-coating cycles provided optimal NO2 response and response time. Consequently, the 0.2 wt % La2O3-loaded WO3 three-cycle spin-coated film offered an ultrahigh response of ∼7213.6 and a response time of ∼31.8 s to 5000 ppb NO2 at a low best sensing temperature of 150 °C in dry air. Moreover, high NO2 selectivity was attained relative to CH2O, HCOOH, CH3OH, C2H5OH, CH3COOH, C6H6, C8H10, C3H6O, C3H7COOH, CH3CHOHCOOH, CH4, C2H4, C2H2, CO2, H2, H2S, and CH3SH. Therefore, the loading of La2O3 nanoparticles on flame-made WO3 sensors was attractive for highly responsive and specific NO2 detections at low working temperatures.