Formaldehyde sensor based on FSP-made AgO_x-doped SnO₂ nanoparticulate sensing films

In this research, 0-1 wt% AgOx-doped SnO2 nanoparticles were developed based on a single-step flame spray pyrolysis process and investigated for formaldehyde (HCHO)-sensing applications. The structural evaluations by X-ray diffraction, X-ray spectroscopy, electron microscopy, nitrogen adsorption and optical absorption indicated that Ag species containing Ag+ and Ag2+ oxidation states could be embedded in 5-20 nm tetragonal SnO2 nanoparticles as secondary AgOx crystals, leading to smaller crystallite size, larger surface area and smaller optical bandgap. From gas-sensing measurements at 200-400 degrees C, AgOx-doping with an optimal Ag content of 0.2 wt% enhanced HCHO response by more than one order of magnitude compared with that of undoped one. In particular, the 0.2 wt% AgOx-doped SnO2 sensing films exhibited a high response of similar to 495-2000 ppm HCHO at 350 degrees C with high selectivity against NH3, NO, C2H2, C2H4, H-2, CH4, C3H6O, C6H6, C2H6O, CH3OH, C7H8 and C8H10. Moreover, the AgOx doped SnO2 sensors displayed good stability and low dependencies of response on temperature and humidity. Thus, the FSP-made 0.2 wt% AgOx-doped SnO2 sensor could be a promising choice for selective and sensitive HCHO detections.