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

In this investigation, flame-made La 2 O 3 -loaded WO 3 nanoparticle films prepared with varying La contents (0–2 wt %) and spin-coating cycle numbers (1–6) were comprehensively explored for nitrogen dioxide (NO 2 ) detection. Detailed material analysis revealed the creation of secondary La 2 O 3 nanoparticles on primary monoclinic WO 3 nanoparticles. Gas-sensing measurements were conducted toward 50–5000 ppb NO 2 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 NO 2 response and response time. Consequently, the 0.2 wt % La 2 O 3 -loaded WO 3 three-cycle spin-coated film offered an ultrahigh response of ∼7213.6 and a response time of ∼31.8 s to 5000 ppb NO 2 at a low best sensing temperature of 150 °C in dry air. Moreover, high NO 2 selectivity was attained relative to CH 2 O, HCOOH, CH 3 OH, C 2 H 5 OH, CH 3 COOH, C 6 H 6, C 8 H 10, C 3 H 6 O, C 3 H 7 COOH, CH 3 CHOHCOOH, CH 4, C 2 H 4, C 2 H 2, CO 2, H 2, H 2 S, and CH 3 SH. Therefore, the loading of La 2 O 3 nanoparticles on flame-made WO 3 sensors was attractive for highly responsive and specific NO 2 detections at low working temperatures.